Dr. John Goff
Publications
Goff, J. A., J. A. Austin, and C. S. Fulthorpe, Reinterpretation of the Franklin "shore" in the Mid-Atlantic Bight as a paleo-shelf edge, Continental Shelf Res., (in press), 2013, #2575
Naveira-Garaboto, A. C., A. J. George Nurser, R. B. Scott, and J. A. Goff, The impact of small-scale topography on the dynamical balance of the ocean, J. Phys. Oceanography, 43, 647-668, 2013, #2544
Santra, M., J. A. Goff, R. J. Steel, and J. A. Austin, Latest Pleistocene growth of the outer New Jersey shelf: Forced regression progradation and lowstand Hudson River paleo-delta system, Marine Geol., (in press), 2013, #2574
Christensen, B., C. R. Alexander, J. A. Goff, J. Turner, and J. A. Austin, The last glacial: Insights from continuous coring on the New Jersey continental shelf, Marine Geol., (in press), 2012, #2542
Goff, J. A., and C. S. Duncan, Reexamination of sand ridges on the middle and outer New Jersey shelf based on combined analysis of multibeam bathymetry and backscatter, seafloor grab samples and chirp seismic data, in Sediments, Morphology and Sedimentary Processes on Continental Shelves: Advances in Technologies, Research and Applications, edited by M. Z. Li, C. R. Sherwood and P. R. Hill, Inter. Assoc. Sedimentologists Spec. Publ., 44, 121-142, 2012, #2076
Goff, J. A., D. E. Lawson, B. A. Willems, M. B. Davis, and S. P. S. Gulick, Morainal bank progradation and sediment accumulation in Disenchantment Bay, Alaska: Response to advancing Hubbard Glacier, J. Geophys. Res., 117, F02031, 2012, doi:10.1029/2011JF002312, #2480 
Morainal banks are primary features at the margins of advancing and stable to quasi-stable temperate tidewater glaciers, yet their roles in glacier dynamics and terminus stability are poorly defined by submarine observations. Analysis of new and archival multibeam data and Landsat images of the advancing Hubbard Glacier, southeast Alaska, reveal that between 1978 and 2010 the ice face and morainal bank advanced together at an average rate of ~34 m/yr, varying spatially and temporally between 14 and 80 m/yr. Morphological features including gullies and a boulder lag suggest cyclical deposition and gravitational erosion on the proximal slope of the morainal bank (15-18 deg), and possible ice pushing in an area without recent sedimentation. In contrast, the morainal bank of the nearby, quasi-stable (surging) Turner Glacier advanced steadily since 1978 by proximal sedimentation on the steep fjord wall below its hanging valley. Sedimentation in the deep (>220 m) basin of Disenchantment Bay increased from 0.88 m/yr spanning 1978 to 1999, to 1.22 m/yr thereafter. This change appears to be a combined response to glacier advance and sediment dispersal farther down-fjord, and to an increase in sediment yield from other glacial and non-glacial sources. Analysis of Hubbard Glacier illustrates the direct correlation between movement of the terminus and morainal bank in advancing the grounding line of a marine-terminating glacier, and that morainal banks provide a fundamental stabilizing role for advance into a deep-water fjord, compensating for changes in water depth at the grounding line.
Sloan, H., D. Sauter, J. A. Goff, and M. Cannat, Abyssal hill characterization at ultra-slow spreading Southwest Indian Ridge, Geochem., Geophys., Geosyst., 13, Q0AE06, 2012, doi:10.1029/2011GC003850, #2476
The morphology of the flanks of the Southwest Indian Ridge holds a record of seafloor formation and abyssal hill generation at an ultraslow spreading rate. Statistical analysis of compiled bathymetry and gravity data from the flanks of the Southwest Indian Ridge from 54ÃÆââ¬Å¡ÃâðE to 67ÃÆââ¬Å¡ÃâðE provides estimates of abyssal hill morphologic character and inferred crustal thickness. The extent of the compiled data encompasses a spreading rate change from slow to ultraslow at ÃÆâÃâ¹Ã¢â¬Â Ãâü24 Ma, a significant inferred variation in sub-axis mantle temperature, and a patchwork of volcanic and non-volcanic seafloor, making the Southwest Indian Ridge an ideal and unique location to characterize abyssal hills generated by ultraslow spreading and to examine the effect of dramatic spreading rate change on seafloor morphology. Root mean square abyssal hill height in ultraslow spreading seafloor ranges from ÃÆâÃâ¹Ã¢â¬Â Ãâü280 m to ÃÆâÃâ¹Ã¢â¬Â Ãâü320 m and is on average ÃÆâÃâ¹Ã¢â¬Â Ãâü80 m greater than found for slow-spreading seafloor. Ultraslow spreading abyssal hill width ranges from ÃÆâÃâ¹Ã¢â¬Â Ãâü4 km to ÃÆâÃâ¹Ã¢â¬Â Ãâü12 km, averaging ÃÆâÃâ¹Ã¢â¬Â Ãâü8 km. Abyssal hill height and width increases west-to-east in both slow and ultraslow spreading seafloor, corresponding to decreasing inferred mantle temperature. Abyssal hills persist in non-volcanic seafloor and extend continuously from volcanic to non-volcanic terrains. We attribute the increase of abyssal hill height and width to strengthening of the mantle portion of the lithosphere as the result of cooler sub-axial mantle temperature and conclude that abyssal hill height is primarily controlled by the strength of the mantle component of the lithosphere rather than spreading rate.
Sauter, D., H. Sloan, M. Cannat, J. A. Goff, P. Patriat, M. Shaming, and W. R. Roest, From slow to ultra-slow: How does spreading rate affect seafloor roughness and crustal thickness?, Geology, 39, 911-914, 2011, doi:10.1130/G32028.1, #2394
We examine the relationship of seafloor roughness and gravity-derived crustal thickness to both spreading rate and inferred mantle temperature using statistical analysis of a multibeam bathymetry and gravity data compilation of the axis and flanks between 54E and 67E at the Southwest Indian Ridge (southwest Indian Ocean). Our findings indicate that root mean square values of abyssal hill heights increase from 220 + or - 20 m to 300 + or - 20 m along flow line corridors that transition a well-constrained full spreading rate change from slow (30 mm/yr) to ultra-slow (15 mm/yr). Mantle Bouguer gravity anomalies, however, indicate no significant change in inferred crustal thickness at the spreading rate transition. In the axis-parallel direction, roughness of both slow and ultra-slow seafloor increases from 54E to 63E while inferred crustal thickness and/or mantle temperature decrease. These findings have implications for the relationship between spreading rate and melt production: they suggest that mantle temperature at slow and ultra-slow ridges may play a more important role than spreading rate in determining seafloor morphology. The lack of evidence for significant crustal thinning accompanying a change from slow to ultra-slow spreading rate lends support to focused subaxial mantle upwelling models.
Scott, R. B., J. A. Goff, A. C. Naveira-Garaboto, and A. J. G. Nurnser, Global rate and spectral characteristics of internal gravity wave generation by geostrophic flow over topography, J. Geophys. Res., 116, C09029, 2011, 3 citations, doi:10.1029/2011JC007005, #2382
The rate of generation of internal gravity waves in the lee of small length scale topography by geostrophic flow in the World Ocean was estimated using linear theory with corrections for finite amplitude topography. Several global data sets were combined for the calculation including an ocean circulation model for the near-bottom geostrophic flow statistics, over 500 abyssal current meter records, historical climatological data for the buoyancy frequency, and two independent estimates of the small scale topographic statistical properties. The first topography estimate was based on an empirically-derived relationship between paleo-spreading rates and abyssal hill roughness, with corrections for sedimentation. The second estimate was based on small-scale (<100~km) roughness of satellite altimetry-derived gravity field, using upward continuation relationships to derive estimates of abyssal hill roughness at the seafloor at scales less than approximately 20~km. The lee wave generation rate was found to be between 0.34 to 0.49~TW. The Southern Hemisphere produced 89% of the lee wave energy, with the Southern Ocean dominating. Strength of the bottom flow was the most important factor in producing the global pattern of generation rate, except in the Indian Ocean where extremely rough topography produced strong lee wave generation despite only moderate bottom flows. The results imply about one half of the mechanical power input to the ocean general circulation from the extra-equatorial wind stress of the World Ocean results from abyssal lee wave generation. Topographic length scales between 176~m and 2.5~km (horizontal wavelengths between 1 and 16~km) accounted for 90% of the globally integrated generation.
Ballard, M. S., K. Becker, and J. A. Goff, Geoacoustic inversion for the New Jersey Shelf: 3-D sediment model, IEEE J. Oceanic Eng., 35, 28-42, 2010, 10 citations, doi:10.1109/JOE.2009.2034490, #2215
A 3-D model of sediment sound speed for a 90-km2 area on the New Jersey shelf was constructed by application of a geoacoustic inversion technique. This approach is based on a combination of seismic reflection measurements and a perturbative inversion scheme using horizontal wave number estimates. In a two-step process, seismic reflection measurements were used to identify depths at which discontinuities in the sound-speed profile (SSP) likely occur. Then, the perturbative inversion algorithm made use of this a priori information by employing qualitative regularization, an optimal method for addressing stability and uniqueness issues associated with solving the ill-posed inversion problem that provides for resolution of the layered seabed structure.
Goff, J. A., and B. K. Arbic, Global prediction of abyssal hill roughness statistics for use in ocean models from digital maps of paleo-spreading rate, paleo-ridge orientation, and sediment thickness, Ocean Modelling, 32, 36-43, 2010, 6 citations, doi:10.1016/j.ocemod.2009.10.001, #2139
Abyssal hills are the dominant small-scale roughness fabric over much of the ocean floor. Created at mid-ocean ridges by combined volcanic and tectonic processes, they are rafted away by plate spreading and modified through time by mass wasting and sedimentation. Abyssal hills are morphological indicators of spreading rate and direction: they are lineated parallel to the ridge at the time of formation, and their heights and widths are inversely correlated to spreading rate. Knowledge of abyssal hill roughness statistics is important for high-resolution models, including models of internal wave generation and mixing driven by tidal and low-frequency flows over the rough bottom. In this paper we present a prediction of abyssal hill roughness statistical parameters world-wide via relationships for the average statistical properties of abyssal hills as a function of spreading rate and direction, and for the modification to these roughness parameters as a function of sediment thickness. These relationships are constrained by new publicly-available digital maps of paleo-spreading rate and direction, and sediment thickness. We also develop a new method for generating synthetic topography with variable statistical properties over a grid, and present an example of synthetic abyssal hill roughness generated for the North Atlantic on a 1/2-min grid.
Goff, J. A., M. A. Allison, and S. P. S. Gulick, Offshore transport of sediment during cyclonic storms: Hurricane Ike (2008), Texas Gulf Coast, USA, Geology, 38, 351-354, 2010, 6 citations, doi:10.1130/G30632.1, #2162
Extreme storms can have a large impact on coastal sediment budgets and the character of strata preserved in the geologic record. Here, we investigate the impact of a cyclonic storm-surge flood and ebb on sediment transport in a microtidal beach barrierâshelf system. Hurricane Ike made landfall on the Texas (United States) coast on 13 September 2008. The accompanying storm surge flooded Galveston Bay with up to 5 m of water above sea level. The surge flood and ebb preferentially flowed over a low-elevation, bay-fronting spit known as the Bolivar Peninsula, destroying buildings and eroding sediments. Surge waters also flowed through Bolivar Roads tidal inlet, the main passageway through the barrier system that separates the gulf and the bay. Bathymetry, Chirp data, and samples were collected in Bolivar Roads tidal inlet 9 to 10 d after the storm, and we compare them here to data collected 4 mo prior. Additional data were collected offshore of Bolivar Peninsula in October 2008. Our results document the dominance of the storm-surge ebb in forcing sediment transport through the inlet, which is not considered in models of beach-barrier evolution. Shoreface sands appear to have been incised by the storm, and advected with beach-barrier sediments sufficiently offshore by the storm-surge ebb that they cannot be reincorporated, indicating a significant loss to the barrier system's sediment budget as a result of a single storm.
Goff, J. A., Global prediction of abyssal hill root-mean-square heights from small-scale altimetric gravity variability, J. Geophys. Res., 115, B12104, 2010, 3 citations, doi:10.1029/2010JB007867, #2334
Abyssal hills, which are pervasive landforms on the seafloor of the Earth's oceans, represent a potential tectonic record of the history of mid-ocean ridge spreading. However, the most detailed global maps of the seafloor, derived from the satellite altimetry-based gravity field, cannot be used to deterministically characterize such small-scale (<10 km) morphology. Nevertheless, the small-scale variability of the gravity field can be related to the statistical properties of abyssal hill morphology using the upward continuation formulation. In this paper, I construct a global prediction of abyssal hill root-mean-square (rms) heights from the small-scale variability of the altimetric gravity field. The abyssal hill-related component of the gravity field is derived by first masking distinct features, such as seamounts, mid-ocean ridges, and continental margins, and then applying a newly designed adaptive directional filter algorithm to remove fracture zone/discontinuity fabric. A noise field is derived empirically by correlating the rms variability of the small-scale gravity field to the altimetric noise field in regions of very low relief, and the noise variance is subtracted from the small-scale gravity variance. Suites of synthetically derived, abyssal hill formed gravity fields are generated as a function of water depth, basement rms heights, and sediment thickness and used to predict abyssal hill seafloor rms heights from corrected small-scale gravity rms height. The resulting global prediction of abyssal hill rms heights is validated qualitatively by comparing against expected variations in abyssal hill morphology and quantitatively by comparing against actual measurements of rms heights. Although there is scatter, the prediction appears unbiased.
Knobles, D. P., J. A. Goff, R. A. Koch, P. S. Wilson, and J. A. Shooter, Effect of inhomogeneous sub-bottom layering on broadband acoustic propagation, IEEE J. Oceanic Eng., 35, 732-743, 2010, 1 citation, doi:10.1109/JOE.2010.2066810, #2293
n this paper, the effects of range inhomogeneities in the seabed layering on low-frequency broadband sound propagation in a shallow-water ocean environment are examined. Acoustic measurements generated by an impulsive sound source were made on the New Jersey continental shelf over propagation paths where previous geophysical analyses provide information on the seabed layering structure. Additional information on the physical properties of the sediment layers, such as sound speed and attenuation, was obtained from previous analyses of continuous wave tow experiments. The seismic and the geophysical information, the inferred geoacoustic information for the sediment layers, and sparse water-column sound-speed measurements provide inputs for a finite element parabolic equation propagation model. For the three propagation paths considered in this study the seabed layering structure for two of the paths is range dependent and the other is approximately horizontally stratified. With this information modeled, time series are produced and are compared in the 35ââ¬â265-Hz band to the measured received times series from impulsive sources deployed at ranges between about 70 and 350 water depths. Further, simulations of the received time series are performed for each of the three paths using modified sub-bottom layering structures for the purpose of quantifying the acoustic field effects associated with deviations of the seabed structure from horizontal stratification.
Goff, J. A., Statistical characterization of Geosat altimetry noise: Dependence on environmental parameters, Geochem., Geophys., Geosyst., 10, Q08007, 2009, 1 citation, doi:10.1029/2009GC002569, #2077
Sea surface height (SSH) measurements from the Geosat satellite altimetry mission are analyzed to statistically characterize their noise process, which is defined here as the small-scale (<50 km), time-varying component of the altimetry data. This analysis is one component of a larger effort to extract meaningful information about seafloor roughness from the small-scale fabric of the altimetric gravity field. Both small-scale seafloor topography (e.g., abyssal hills) and SSH noise significantly influence the measured gravity fabric. Hence, a global, quantitative understanding of SSH noise is required to infer what portion of the gravity fabric is associated with the true geoid. It is also anticipated that the SSH noise analysis will prove useful in designing improvements to altimetry processing algorithms. The SSH data are first processed by differencing nearest-neighbor tracks, to minimize the static component of variability, and then by high-pass filtering, to remove variability associated with mesoscale oceanic circulation. Autocovariance analysis reveals that SSH noise can be decomposed into uncorrelated (white noise) and correlated, semiperiodic components. Three parameters are measured which characterize the variance of both components and the correlation length of the correlated component. The global distribution of uncorrelated noise variance is closely correlated to significant wave heights, directly linking the uncertainty of the altimeter return time to the roughness of the sea surface. The variance and correlation length of the correlated component of noise can be associated with three separate environmental parameters: sea ice, precipitation rates, and upper atmospheric variability associated with the subtropical jet stream. As widely differing as these environmental processes are, it is hypothesized that features like sea ice, rain storms, and atmospheric turbulence can cause sudden perturbations in the return time of the altimetry signal, creating decaying oscillations associated with the onboard tracking algorithms.
Goff, J. A., and J. A. Austin, Seismic and bathymetric evidence for four different episodes of iceberg scouring on the New Jersey outer shelf: Possible correlation to Heinrich events, Marine Geol., 266, 244-254, 2009, 6 citations, doi:10.1016/j.margeo.2009.08.012, #2081
Re-analysis of dense CHIRP seismic surveys on the outer New Jersey shelf reveals two sets of shallowly buried incisions. The incisions are linear to slightly sinuous, oriented ~NEâSW, and exhibit cross-cutting relationships. We interpret both sets as paleo-iceberg scours. One set cuts into the âRâ horizon, a regional unconformity that formed ~ 45â40 ka, and which was subsequently buried by the finer-grained outer shelf sediment wedge (OSW). The second set is part of an erose boundary between a layered, lower unit of the OSW and an upper, more transparent unit. The erose boundary scours are deeper and have steeper slopes than the âRâ horizon scours. The latter often exhibit bermed edges, whereas the former do not. These differences in cross-sectional morphology are likely determined by the material properties of the sediments being scoured: sand at the âRâ horizon, and clay at the erose boundary. The orientation of both sets of scours is consistent with previously recognized iceberg scours in stratigraphically younger seafloor on the outer New Jersey shelf in ~ 110â150 m water depths, located ~ 40 km to the northeast. We argue that Heinrich events, recurring periods of massive iceberg flux into the North Atlantic, represent the most likely times for transporting icebergs to these latitudes. Based on stratigraphic relationships, a recently published ambient sea level curve and radiocarbon age constraints, we attribute the âRâ horizon scours to Heinrich event H4 (~ 37 cal ka), the erose boundary scours to H3 (~ 30 cal ka), and the seafloor scours to H2 (~ 23 cal ka) and/or H1 (~ 17 cal ka). Facies changes immediately following the âRâ horizon and erose boundary scours may be related to Heinrich event-forced climate changes, perhaps the onset of interstadial conditions and associated melt-water pulses/floods; these pulses/floods repeatedly carried fine-grained rock flour produced by widespread glacial erosion to the New Jersey shelf.
Nordfjord, S., J. A. Goff, J. A. Austin, and C. S. Duncan, Shallow stratigraphy and complex transgressive ravinement on the New Jersey middle and outer continental shelf, Marine Geol., 266, 232-243, 2009, 7 citations, doi:10.1016/j.margeo.2009.08.010, #2080
The ravinement surface is a key marker for examining the effects of the most recent sea-level transgression on development of the latest PleistoceneâHolocene stratigraphic record of the New Jersey middle and outer continental shelf. This surface is marked by a moderate-amplitude reflector, identified as the âTâ horizon in chirp seismic data, which caps filled incised valleys formed during or soon after the Last Glacial Maximum (LGM) and eustatic lowstand, and also serves as the base of a Holocene sand sheet. The âTâ horizon is clearly erosional; we interpret it as marking landward migration of the shore zone across the coastal plain during the earliest-mid Holocene. We use chirp seismic surveys acquired in 1999 and 2001 to map the geomorphology of the âTâ horizon over a ~ 100 by 60 km region. Shallow, bathymetric contour-parallel depressions, ~ 10 km wide and ~ 8 m deep, are present in the horizon at ~ 50â60 m and ~ 70 m water depths; we interpret them as preserved lagoonal/back-barrier topography; portions of filled tidal channels occur in these depressions. Perhaps these depressions represent pauses in the retreat of the shoreline, either as a result of eustatic fluctuations or slope steepening, allowing for formation of back-barrier/lagoonal features substantive enough to resist complete destruction by subsequent ravinement. Alternatively, they may be locations of local flattening in the antecedent topography that forced rapid drowning and preservation of back-barrier morphology. These paleo-estuarine/back-barrier features may also be more susceptible to erosion during transgression, so the presence of these depressions might have focused marine erosion in some way, perhaps by promoting near-bottom turbulence during storm events.
Choi, J. W., P. H. Dahl, and J. A. Goff, Observations of the R reflector and sediment interface reflection at the Shallow Water '06 central site, J. Acoustical Soc. Amer., 124, EL128-EL134, 2008, 8 citations, doi:10.1121/1.2963048, #1989
Acoustic bottom-interacting measurements from the Shallow Water '06 experiment experiment (frequency range 1â20 kHz) are presented. These are co-located with coring and stratigraphic studies showing a thin (~20 cm) higher sound speed layer overlaying a thicker (~20 m) lower sound speed layer ending at a high-impedance reflector (R reflector). Reflections from the R reflector and analysis of the bottom reflection coefficient magnitude for the upper two sediment layers confirm both these features. Geoacoustic parameters are estimated, dispersion effects addressed, and forward modeling using the parabolic wave equation undertaken. The reflection coefficient measurements suggest a nonlinear attenuation law for the thin layer of sandy sediments.
Goff, J. A., C. Jenkins, and S. J. Williams, Seabed mapping and characterization of seabed variability using the usSEABED data base, Continental Shelf Res., 28, 614-633, 2008, 5 citations, doi:10.1016/j.csr.2007.11.011, #1898
We present a methodology for statistical analysis of randomly located marine sediment point data, and apply it to the US continental shelf portions of usSEABED mean grain size records. The usSEABED database, like many modern, large environmental datasets, is heterogeneous and interdisciplinary. We statistically test the database as a source of mean grain size data, and from it provide a first examination of regional seafloor sediment variability across the entire US continental shelf. Data derived from laboratory analyses (âextractedâ) and from word-based descriptions (âparsedâ) are treated separately, and they are compared statistically and deterministically. Data records are selected for spatial analysis by their location within sample regions: polygonal areas defined in ArcGIS chosen by geography, water depth, and data sufficiency. We derive isotropic, binned semivariograms from the data, and invert these for estimates of noise variance, field variance, and decorrelation distance. The highly erratic nature of the semivariograms is a result both of the random locations of the data and of the high level of data uncertainty (noise). This decorrelates the data covariance matrix for the inversion, and largely prevents robust estimation of the fractal dimension. Our comparison of the extracted and parsed mean grain size data demonstrates important differences between the two. In particular, extracted measurements generally produce finer mean grain sizes, lower noise variance, and lower field variance than parsed values. Such relationships can be used to derive a regionally dependent conversion factor between the two. Our analysis of sample regions on the US continental shelf revealed considerable geographic variability in the estimated statistical parameters of field variance and decorrelation distance. Some regional relationships are evident, and overall there is a tendency for field variance to be higher where the average mean grain size is finer grained. Surprisingly, parsed and extracted noise magnitudes correlate with each other, which may indicate that some portion of the data variability that we identify as ânoiseâ is caused by real grain size variability at very short scales. Our analyses demonstrate that by applying a bias-correction proxy, usSEABED data can be used to generate reliable interpolated maps of regional mean grain size and sediment character.
Knobles, D. P., P. S. Wilson, J. A. Goff, and S. E. Cho, Seabed acoustics of a sand ridge on the New Jersey continental shelf, J. Acoustical Soc. Amer., 124, EL151-EL156, 2008, 13 citations, doi:10.1121/1.2960977, #2023
Acoustic measurements were made on a sand ridge on the New Jersey continental shelf. Data collected on two L arrays separated by 20 km from a single multi-frequency tow suggest small horizontal environmental variability. Values for the sound speed structure of the seabed are extracted by first applying a geo-acoustic inversion method to broadband and narrowband acoustic data from short-range sources. Then, a parabolic equation algorithm is used to properly include the bathymetry and sub-bottom layering. Finally, the frequency dependence of the seabed attenuation is inferred by optimizing the model fit to long-range transmission loss data in the 50â3000 Hz band.
Miselis, J., P. T. Gayes, J. A. Goff, T. Rodriguez, D. Krantz, J. McNinch, J. C. Hill, and C. R. Alexander, Synthesizing regional shallow-water geophysical data for shoreline evolution models, Eos, Trans. Amer. Geophys. Un., 89, 2008, doi:10.1029/2008EO410007, #2022
Shallow Coastal Stratigraphy Workshop; Conway, South Carolina, 9â10 July 2008; Numerous regional geophysical mapping efforts have taken place along the mid-Atlantic coast over the past 20 years, illuminating the relationship between relict geology and coastal processes. Results have demonstrated that variability in the structural framework of the coastal plain is important in controlling regional-scale shoreline evolution and sediment availability. Furthermore, variations in the geologic character (grain size, consolidation, composition, morphology, etc.) of the shelf and nearshore have been linked to long-term (centennial and greater) and short-term (decadal to centennial) shoreline evolution. Despite these spatial relationships, little information regarding the variability of geologic properties is accounted for in numerical models of shoreline change, leading to outputs that do not accurately characterize natural and human-induced shoreline behavior.
Green, A. N., J. A. Goff, and R. Uken, Geomorphological evidence for upslope canyon-forming processes on the northern KwaZulu-Natal shelf, SW Indian ocen, South Africa, Geo-Marine Lett., 27, 399-409, 2007, 12 citations, doi:10.1007/s00367-007-0082-2, #1870
A geomorphological and statistical analysis of slope canyons from the northern KwaZulu-Natal continental margin is documented and compared with submarine canyons from the Atlantic margin of the USA. The northern KwaZulu-Natal margin is characterized by increasing upslope relief, concave slope-gradient profiles and features related to upslope growth of the canyon forms. Discounting slope-gradient profile, this morphology is strikingly similar to canyon systems of the New Jersey slope. Several phases of canyon incision indicate that downslope erosion is also an important factor in the evolution of the northern KwaZulu-Natal canyon systems. Despite the strong similarities between the northern KwaZulu-Natal and New Jersey slope-canyon systems, key differences are evident: (1) the concavity of the northern KwaZulu-Natal slope, contrasting with the ∼linear New Jersey slope; (2) the relative isolation of the northern KwaZulu-Natal canyons, rather than the dense clustering of the New Jersey canyons; and (3) the absence of strongly shelf-breaching canyons along the northern KwaZulu-Natal margin. In comparison with the New Jersey margin, we surmise a more youthful stage of canyon evolution, a result of either the canyons themselves being younger or the formative processes being less active. Less complicated patterns of erosion resulting from reduced sediment availability have developed in northern KwaZulu-Natal. The reduction in slope concavity on the New Jersey margin may be the result of grading of the upper slope by intensive headward erosion, a process more subduedÃÆââââ¬Å¡Ã¬Ã¢ââ¬ÃÂor less evidentÃÆââââ¬Å¡Ã¬Ã¢ââ¬ÃÂon the KwaZulu-Natal margin.
Tang, D. J., J. N. Moum, J. F. Lynch, P. Abbot, R. Chapman, P. H. Dahl, T. F. Duda, G. Gawarkiewicz, S. Glenn, J. A. Goff, H. Graber, J. Kemp, A. Maffei, J. D. Nash, and A. Newhill, Shallow Water '06: A joint acoustic propagation/nonlinear internal wave physics experiment, Oceanography, 20 (4), 156-167, 2007, 39 citations, #1945
Goff, J. A., C. Jenkins, and B. Calder, Maximum a posteriori resampling of noisy, spatially correlated data, Geochem., Geophys., Geosyst., 7, Q08003, 2006, 7 citations, doi:10.1029/2006GC001297, #1821
In any geologic application, noisy data are sources of consternation for researchers, inhibiting interpretability and marring images with unsightly and unrealistic artifacts. Filtering is the typical solution to dealing with noisy data. However, filtering commonly suffers from ad hoc (i.e., uncalibrated, ungoverned) application. We present here an alternative to filtering: a newly developed method for correcting noise in data by finding the âbestâ value given available information. The motivating rationale is that data points that are close to each other in space cannot differ by âtoo much,â where âtoo muchâ is governed by the field covariance. Data with large uncertainties will frequently violate this condition and therefore ought to be corrected, or âresampled.â Our solution for resampling is determined by the maximum of the a posteriori density function defined by the intersection of (1) the data error probability density function (pdf) and (2) the conditional pdf, determined by the geostatistical kriging algorithm applied to proximal data values. A maximum a posteriori solution can be computed sequentially going through all the data, but the solution depends on the order in which the data are examined. We approximate the global a posteriori solution by randomizing this order and taking the average. A test with a synthetic data set sampled from a known field demonstrates quantitatively and qualitatively the improvement provided by the maximum a posteriori resampling algorithm. The method is also applied to three marine geology/geophysics data examples, demonstrating the viability of the method for diverse applications: (1) three generations of bathymetric data on the New Jersey shelf with disparate data uncertainties; (2) mean grain size data from the Adriatic Sea, which is a combination of both analytic (low uncertainty) and word-based (higher uncertainty) sources; and (3) side-scan backscatter data from the Martha's Vineyard Coastal Observatory which are, as is typical for such data, affected by speckle noise. Compared to filtering, maximum a posteriori resampling provides an objective and optimal method for reducing noise, and better preservation of the statistical properties of the sampled field. The primary disadvantage is that maximum a posteriori resampling is a computationally expensive procedure.
Livingston, E. S., J. A. Goff, S. Finette, P. Abbot, J. F. Lynch, and W. S. Hodgkiss, Capturing uncertainty in the tactical ocean environment, IEEE J. Oceanic Eng., 31, 245-248, 2006, 3 citations, doi:10.1109/JOE.2006.878579, #1946
Merwade, V. M., D. R. Maidment, and J. A. Goff, Anisotropic considerations while interpolating river channel bathymetry, J. Hydrology, 331, 731-741, 2006, 14 citations, doi:10.1016/j.jhydrol.2006.06.018, #1823
Numerical modeling of flow dynamics in river channels may require the spatial interpolation of scattered measurements of bathymetry elevation to obtain elevations at computational mesh nodes. This paper examines the various spatial interpolation methods used in interpolating river channel bathymetry. Commonly used interpolation methods, namely inverse distance weighting, spline (tension and regularized), natural neighbor, TopoGrid, and ordinary kriging (isotropic and anisotropic) are evaluated within the ArcGIS environment by using root mean square error (RMSE) criteria. To study the anisotropic effects, the interpolation methods are evaluated in two different coordinate systems: a Cartesian (x, y) coordinate system and a flow-oriented (s, n) coordinate system. Using the data from the Brazos River in Texas, it is shown that TopoGrid, natural neighbor and ordinary kriging, which do not account of anisotropy in the data, performed better than anisotropic kriging in the Cartesian coordinate system. In the flow-oriented coordinate system, the performance of anisotropic spatial interpolation methods is significantly better (40% reduction in RMSE) compared to the isotropic interpolation methods. A modified version of inverse distance weighting method, called elliptical inverse distance weighting (EIDW), is developed to account for river anisotropy. The RMSE results from application of EIDW are close to that from anisotropic kriging, thus providing a simple and computationally faster alternative to complex kriging methods.
Nordfjord, S., J. A. Goff, J. A. Austin, and S. P. S. Gulick, Seismic facies of incised-valley fills, New Jersey continental shelf: Implications for erosion and preservation processes acting during latest Pleistocene-Holocene transgression, J. Sedimentary Res., 76, 1284-1303, 2006, 16 citations, doi:10.2110/jsr.2006.108, #1819
Incised-valley fills shallowly buried beneath the New Jersey middleâouter shelf reveal a retrogradational shift of four seismic facies, as observed in 1â4 kHz deep-towed chirp seismic data. These facies, the only preserved stratigraphic record of the latest QuaternaryâHolocene drowning and infilling of fluvial drainage systems developed on this exposed shelf at or near the Last Glacial Maximum (LGM), are interpreted as (1) fluvial lag deposits, SF1; (2) estuarine mixed sand and muds, SF2; (3) estuary central bay muds, SF3; and (4) redistributed estuary-mouth sands, SF4. These fills are truncated by a transgressive ravinement, the T horizon, which is in turn overlain by Holocene marine sand deposits. The seismic facies are bounded by reflectors marking either source diastems or unconformities: (1) the Channels horizon is the lowstand fluvial incision surface, (2) B1 is a bay flooding surface, (3) B2 is an intra-estuarine depositional surface, (4) B3 is a tidal ravinement surface, and (5) the T horizon represents erosion at or near the shoreface during Holocene transgression. The Channels horizon is generally preserved only in valley axes. Elsewhere, this sequence boundary has been modified by surfaces B1 and/or B3. Dip-oriented changes in the thickness of SF3 and SF4 suggest either a stillstand in the passage of the shoreline, which allowed such spatial variations, or that local valley shape controlled hydrodynamic conditions for sediment transport and deposition. Narrower valleys may have promoted tidally dominated, fine-grained deposition within these drowning estuaries, while broader valleys attenuated tidal flow velocities and allowed the filling of the estuary to be dominated by wave and current energy, promoting more coarse-grained deposition. Our study demonstrates that wave- and tide-dominated estuarine facies can coexist within such fill strata.
Goff, J. A., J. A. Austin, S. P. S. Gulick, S. Nordfjord, B. Christensen, C. K. Sommerfield, H. C. Olson, and C. R. Alexander, Recent and modern marine erosion on the New Jersey outer shelf, Marine Geol., 216, 275-296, 2005, 26 citations, doi:10.1016/j.margeo.2005.02.015, #1756
Goff, J. A., L. A. Mayer, P. Traykovski, I. Buynevich, R. H. Wilkens, R. Raymond, G. Glang, R. L. Evans, H. C. Olson, and C. Jenkins, Detailed investigation of sorted bedforms, or 'rippled scour depressions', within the Martha's Vineyard Coastal Observatory, Massachusetts, Continental Shelf Res., 25, 461-484, 2005, 33 citations, doi:10.1016/j.csr.2004.09.019, #1876
We examine in detail the seafloor and cross-sectional morphology of sorted bedforms (i.e., ârippled scour depressionsâ) in the Martha's Vineyard Coastal Observatory (MVCO). Sorted bedforms are seen as alternating bands of coarse and fine sands oriented nearly perpendicular to the shoreline. The coarse sand zones (CSZs) of the sorted bedforms are tens to hundreds of meters wide, and extend up to several kilometers from the shoreface. Data considered here include time series of swath backscatter and bathymetry, high resolution chirp seismic reflection, and grain-size analyses from grab samples, vibracores and push cores. The sorted bedforms observed within the MVCO survey area exhibit a broad spectrum of bathymetric relief (from 10 cm to 3 m), grain-size contrast (from 250 to>2000 μm) and morphologic form (moats, steps, and dune forms). All forms observed display lateral asymmetry in both grain size and bathymetric expression. In general, grain size is largest and bathymetry is deepest toward one side, typically seen in the backscatter maps as the more well defined of the two CSZ edges where that distinction can be made. These observations are consistent with earlier studies suggesting that sorted bedforms are a response to a transverse, alongshore flow. Within the MVCO survey area, the sense of asymmetry changes polarity going from west/shallow water to east/deeper water, suggesting a complex hydrographic regime.
Gulick, S. P. S., J. A. Goff, J. A. Austin, C. R. Alexander, S. Nordfjord, and C. S. Fulthorpe, Basal inflection-controlled shelf-edge wedges off New Jersey track sea-level fall, Geology, 33, 429-432, 2005, 14 citations, doi:10.1130/G21310.1, #1741
A key marker for examining the latest Pleistocene history of the New Jersey margin is the high-amplitude, long-recognized R-horizon reflector. This time-transgressive surface was formed 47â 33 ka and represents the integrated topographic and bathymetric surface developed during the complicated sea-level oscillation associated with the regression that preceded the Last Glacial Maximum (LGM). From landward to seaward across the outer shelf, the R reflector changes from subhorizontal, in most locations <9 m beneath the modern seafloor, to seaward dipping, forming the base of two offlapping sediment wedges: the previously described outer-shelf wedge and a deep-shelf wedge seaward of it. This transition occurs across two inflection zones, where the dip of the R reflector steepens seaward, that can be traced for tens of kilometers along strike and mark the landward limits of these wedges. These inflection zones are possibly former wave-dominated shorefaces; these represent the primary topographic elements present during the last regression. We speculate that these inflections dictated both the locations for deposition of the two prograding, offlapping wedges that developed during the complex sea-level fall prior to the LGM and their successive erosion before and after the LGM. We suggest that such inflection zones and their associated wedges are important markers of regression in clastic-dominated outer-shelf settings along passive margins.
Nordfjord, S., J. A. Goff, J. A. Austin, and C. K. Sommerfield, Seismic geomorphology of buried channel systems on the New Jersey outer shelf: Assessing past environmental conditions, Marine Geol., 214, 339-364, 2005, 27 citations, doi:10.1016/j.margeo.2004.10.035, #1711
Quantitative geomorphologic analysis of shallowly buried, dendritic channel systems on the New Jersey shelf provides estimates of paleo-hydrologic parameters needed to link channel morphology to the former hydrodynamic setting. These channels, observed in 1â4 kHz deep-towed chirp seismic data, formed presumably as fluvial systems when the shelf was exposed during the Last Glacial Maximum (LGM). The presumed fluvial origin of these channels is supported by their incision into underlying Pleistocene strata, a chaotic seismic fill unit at their bases which may be indicative of non-marine gravel lag, and measured stream junction angles that are consistent with a riverine origin. The channels would also have been subjected to estuarine/tidal environments during ensuing sea-level rise. We employ empirically derived hydraulic equations for modern rivers and estuaries to estimate paleo-discharges, velocities and maximum shear stresses, using the preserved and interpolated paleo-channel geometries as a guide. Generally, trunk/main channels have box-like, symmetric cross-sections, with width/depth ratios of >100, whereas smaller, tributary channels have more v-shaped, asymmetric cross-sections with width/depth ratios of 40â70. The high width/depth ratios, along with low sinuosities (1.1) and slopes (<0.02°), are consistent with braided streams as specified by a modern river classification system. However, the channels show no evidence of braiding. We hypothesize instead that these channel systems are immature, having had insufficient time to develop high sinuosities that would otherwise be expected before they were drowned by the Holocene transgression. Mean paleo-flow estimates for these systems assuming a tidal environment (1.0â1.5 m/s) are consistent with modern tidal creeks comparable to the sizes of channels observed here (<2 km wide and <25 m deep). Estimated tidal shear stresses would be sufficient to initiate sediment transport of grains 2â8 mm in diameter (coarse sand and fine gravel) as bedload and finer grained material in suspension. However, paleo-flow estimates assuming a fluvial environment (1.1â2.0 m/s) are generally too high for a non-tidal creek, given the presumed low hydraulic gradients in this coastal plain setting. Retrodicted fluvial discharge and boundary shear stresses would have been sufficient to transport particles up to 15 mm in diameter (gravel) as bedload; these grain sizes are too coarse to be transported by sluggish coastal plain rivers. We conclude that either flows were quite high when this system was first incised fluvially, perhaps due to meltwater pulses following the LGM, or that tidal influences have modified the original fluvial geometry.
Ratilal, P., Y. Lai, D. T. Symonds, L. A. Ruhlmann, J. R. Preston, E. K. Scheer, M. T. Garr, C. W. Holland, J. A. Goff, and N. C. Makris, Long range acoustic imaging of the continental shelf environment: The Acoustic Clutter Reconnaissance Experiment 2001, J. Acoustical Soc. Amer., 117, 1977-1998, 2005, 21 citations, doi:10.1121/1.1799252, #1947
An active sonar system is used to image wide areas of the continental shelf environment by long-range echo sounding at low frequency. The bistatic system, deployed in the STRATAFORM area south of Long Island in AprilâMay of 2001, imaged a large number of prominent clutter events over ranges spanning tens of kilometers in near real time. Roughly 3000 waveforms were transmitted into the water column. Wide-area acoustic images of the ocean environment were generated in near real time for each transmission. Between roughly 10 to more than 100 discrete and localized scatterers were registered for each image. This amounts to a total of at least 30 000 scattering events that could be confused with those from submerged vehicles over the period of the experiment. Bathymetric relief in the STRATAFORM area is extremely benign, with slopes typically less than 0.5° according to high resolution (30 m sampled) bathymetric data. Most of the clutter occurs in regions where the bathymetry is locally level and does not coregister with seafloor features. No statistically significant difference is found in the frequency of occurrence per unit area of repeatable clutter inside versus outside of areas occupied by subsurface river channels.
Goff, J. A., W. H. F. Smith, and K. M. Marks, The contributions of abyssal hill morpholgy and noise to altimetric gravity fabric, Oceanography, 17 (1), 24-37, 2004, #1681
Goff, J. A., and S. Nordfjord, Interpolation of fluvial morphology using channel-oriented coordinate transformation: A case study from the New Jersey shelf, Mathematical Geol., 36, 643-658, 2004, 11 citations, doi:10.1023/B:MATG.0000039539.84158.cd, #1685
We present a new methodology for interpolating channel morphology that incorporates a transformation from geographic to channel-based coordinate systems. Interpolation in the transformed space enables enforcement of downstream continuity of morphology and edge delineation through any changes in channel direction. The transformation is guided by a channel center line, which approximately tracks the path of the channel through geographic space; coordinates are given in distance along and across the center line. Accurate interpolation requires a track line density sufficient to unambiguously trace channels from one track line to the next. Channel continuity is ensured by first interpolating along paths defined by the channel thalweg and edges, which must be chosen by the user, and along several interim paths between the edges and thalweg. The completed interpolations for each channel are transformed back into geographic coordinates, and channel confluence is handled through a maximum depth criterion. The method is applied here to shallowly buried channels mapped with high-resolution chirp seismic data on the New Jersey shelf, but should be applicable to a wide range of subaerial and buried fluvial systems.
Goff, J. A., B. J. Kraft, L. A. Mayer, S. G. Schock, C. K. Sommerfield, H. C. Olson, S. P. S. Gulick, and S. Nordfjord, Seabed characterization on the New Jersey middle and outer shelf: Correlatability and spatial variability of seafloor sediment properties, Marine Geol., 209, 147-172, 2004, 61 citations, doi:10.1016/j.margeo.2004.05.030, #1689
Nearly 100 collocated grab samples and in situ 65 kHz acoustic measurements were collected on the New Jersey middle and outer shelf within an area that had previously been mapped with multibeam backscatter and bathymetry data, and more recently with chirp seismic reflection profiling. Eighteen short cores were also collected and probed for resistivity-based porosity measurements. The combined data set provides a basis for empirically exploring the relationship among the remotely sensed data, such as backscatter and reflection coefficients, and directly measured seabed properties such as grain size distribution, velocity, attenuation and porosity. We also investigate the spatial variability of these properties through semi-variogram analysis to facilitate acoustic modeling of natural environmental variability.
Grain size distributions on the New Jersey shelf are commonly multi-modal, leading us to separately characterize coarse % (>4 mm), fine % (<63 μm) and mean sand grain size to quantify the distribution. We find that the backscatter is dominated by the coarse component (expressed as weight %), typically shell hash and occasionally terrigenous gravel. In sediment types where coarse material is not significant, backscatter correlates with velocity and fine weight %. Mean sand grain size and fine % are partially correlated with each other, and combined represent the primary control on velocity. The fine %, rather than mean grain size as a whole, appears to be the primary control on attenuation, although coarse % may increase attenuation marginally through scattering. Vertical-incidence seismic reflection coefficients, carefully culled of unreliable values, exhibit a strong correlation with the in situ velocity measurements, suggesting that such data may prove more reliable than backscatter at deriving sediment physical properties from remote sensing data. The velocity and mean sand grain size semi-variograms can be fitted with a von Kármán statistical model with horizontal scale 12.6 km, which provides a basis for generating synthetic realizations. The backscatter and coarse % semi-variograms exhibit two horizontal scales: one 8 km and the other too small to quantify with available data.
Hill, J. C., N. W. Driscoll, J. K. Weissel, and J. A. Goff, Large-scale elongated gas blowouts along the U.S. Atlantic margin, J. Geophys. Res., 109, B09101, 2004, 10 citations, doi:10.1029/2004JB002969, #1690
n May 2000 we surveyed a series of en echelon, asymmetric depressions along the outer shelf off Virginia and North Carolina using high-resolution chirp and side-scan sonar. The features, which are elongated parallel to the shelf edge and have steep landward walls, are ∼4 km long, 1 km wide, and up to 50 m deep. On the basis of internal stratal geometry interpreted from chirp profiles, the depressions do not appear to result from simple, down-to-the-east, normal displacement along deep-seated faults or structure. Rather, the depressions seem to have been excavated primarily by gas expulsion, creating large-scale asymmetric gas escape structures that have been termed âgas blowouts.â Gas appears to have been trapped beneath a shelf edge delta that is a few tens of meters thick and exhibits internal soft sediment deformation suggestive of progressive downslope (seaward) creep. These new data suggest the blowouts occurred when thin-skinned deformation and creep of the surficial deltaic sediment layers combined with updip/upslope gas migration, ultimately leading to gas pressure in excess of the overburden. The location of the expulsion craters along the shelf edge and their elongated, asymmetric shapes strongly suggests a causal relation between the downslope creep of the delta and the expulsion event. We suggest a positive feedback between upward migration of gas-rich fluids through the low-stand delta and the downslope creep processes. While the complex interplay between differential permeability, overpressure, and upslope fluid migration remains poorly understood, we suggest such interactions may play an important role in controlling slope stability.
Goff, J. A., and K. Holliger, (Editors), Heterogeneity in the Crust and Upper Mantle: Nature, Scaling, and Seismic Properties, Klewer Academic/Plenum, 349 pp., 2003, #1649
Goff, J. A., and W. H. F. Smith, A correspondence of altimetric gravity texture to abyssal hill morphology along the flanks of the southeast Indian ridge, Geophys. Res. Lett., 30, 2269, 2003, 6 citations, doi:10.1029/2003GL018913, #1678
We examine the relationship between altimetric gravity and abyssal hill textures along the flanks of Southeast Indian Ridge, where previous studies observed a progressive west-to-east increase in abyssal hill roughness and scales. Such a relationship is often considered unlikely because abyssal hills are typically smaller than upward continuation filter scales. However, our results, which exclude ridges, fracture zones and large pseudofaults, show that altimetric gravity roughness and characteristic scales in this region also increase from west to east and, at the largest scales, gravity texture exhibits ridge-parallel lineaments. Synthetic profiles also demonstrate how the texture parameters of a filtered field are related to those of the unfiltered field, particularly where the characteristic scale of the latter is smaller than the filter length.
Holliger, K., and J. A. Goff, A generic model for the 1/f nature of seismic velocity fluctuations, in Heterogeneity in the Crust and Upper Mantle: Nature, Scaling and Seismic Properties, ed. by J. A. Goff and K. Holliger, Kluwer Academic/Plenum, New York, 131-154, 2003, #1599
Goff, J. A., R. A. Wheatcroft, H. Lee, D. E. Drake, D. J. P. Swift, and S. Fan, Spatial variability of shelf sediments in the STRATAFORM natural laboratory, Northern California, Continental Shelf Res., 22, 1199-1223, 2002, 9 citations, doi:10.1016/S0278-4343(01)00097-8, #1589
The âCorrelation Length Experimentâ, an intensive box coring effort on the Eel River shelf (Northern California) in the summer of 1997, endeavored to characterize the lateral variability of near-surface shelf sediments over scales of meters to kilometers. Coring focused on two sites, K60 and S60, separated by 15 km along the 60 m isobath. The sites are near the sand-to-mud transition, although K60 is sandier owing to its proximity to the Eel River mouth. Nearly 140 cores were collected on dip and strike lines with core intervals from <10 m to 1 km. Measurements on each core included bulk density computed from gamma-ray attenuation, porosity converted from resistivity measurements, and surficial grain size. Grain size was also measured over the full depth range within a select subset of cores. X-radiograph images were also examined. Semi-variograms were computed for strike, dip, and down-hole directions at each site. The sand-to-mud transition exerts a strong influence on all measurements: on average, bulk density increases and porosity decreases with regional increases in mean grain size. Analysis of bulk density measurements indicates very strong contrasts in the sediment variability at K60 and S60. No coherent bedding is seen at K60; in the strike direction, horizontal variability is âwhiteâ (fully uncorrelated) from the smallest scales examined (a few meters) to the largest (8 km), with a variance equal to that seen within the cores. In contrast, coherent bedding exists at S60 related to the preservation of the 1995 flood deposit. A correlatable structure is found in the strike direction with a decorrelation distance of 800 m, and can be related to long-wavelength undulations in the topography and/or thickness of the flood layer or overburden. We hypothesize that the high degree of bulk density variability at K60 is a result of more intense physical reworking of the seabed in the sandier environment. Without significant averaging, the resistivity-based porosity measurements are only marginally correlated to gamma-ray-bulk density measurements, and are largely independent of mean grain size. Furthermore, porosity displays a high degree of incoherent variability at both sites. Porosity, with a much smaller sample volume than bulk density, may therefore resolve small-scale biogenic variability which is filtered out in the bulk density measurement.
Duncan, C. S., and J. A. Goff, Relict iceberg keel marks on the New Jersey outer shelf, southern Hudson apron, Geology, 29, 411-414, 2001, 13 citations, doi:10.1130/0091-7613(2001)029<0411:RIKMOT>2.0.CO;2, #1540
Swath sonar bathymetry reveals sinuous furrows, <100 to >400 m wide, kilometers long, and <1 m to >4 m deep inscribed in semilithified clays on the southern Hudson apron. We interpret these as keel marks created by floating icebergs detached from the retreating Laurentide ice sheet since ca. 25 ka. Keel-mark orientations suggest two phases of iceberg rafting. These phases could correlate with Heinrich meltwater events H2 and H1 ca. 25 and 17 ka, bracketing the late Wisconsinan glacial maximum ca. 22 ka. During Holocene transgression, some keel marks were reworked and reformed into oblique ridges where older, sandier sediments crop out at the seafloor. Relict glacial features on the New Jersey outer shelf provide a tie between the timing of Laurentide glacial retreat and the evolution of shallow stratigraphy on this mid-latitude shelf during the last global sea-level cycle (ca. 120 ka to present).
Goff, J. A., Quantitative classification of canyon systems on continental slopes and a possible relationship to slope curvature, Geophys. Res. Lett., 28, 4359-4362, 2001, 18 citations, doi:10.1029/2001GL013300, #1554
A recent analysis of continental slopes (Adams and Schlager, 2000) has established three basic shapes for classification: exponential, linear, and Gaussian. Examples of each of these shapes can be found on the middle US Atlantic margin, where sufficiently high‐quality bathymetry data are available to investigate the systems of erosional canyons that incise the slopes. Significant morphological differences can be noted visually in these examples, suggesting that canyon systems can be classified in a quantitative manner. Here it is proposed that canyon system morphology can be distinguished by the downslope progression of cross‐slope statistical parameters, particularly RMS relief. On the linear slope, rms relief decreases with depth, whereas rms relief increases on the exponentially shaped slope. On the Gaussian shaped slope, rms relief is roughly constant, with minor variations. This straightforward method of classification may hold great promise for systematically investigating relationships between slope canyons and their formative environments.
Driscoll, N. W., J. K. Weissel, and J. A. Goff, Potential for large-scale submarine slope failure and tsunami generation along the U.S. mid-Atlantic coast, Geology, 28, 407-410, 2000, 50 citations, doi:10.1130/0091-7613(2000)28<407:PFLSSF>2.0.CO;2, #1491
The outer continental shelf off southern Virginia and North Carolina might be in the initial stages of large-scale slope failure. A system of en echelon cracks, resembling small-offset normal faults, has been discovered along the outer shelf edge. Swath bathymetric data indicate that about 50 m of down-to-the-east (basinward) normal slip has occurred on these features. From a societal perspective, we need to evaluate the degree of tsunami hazard that might be posed by a major submarine landslide, such as the nearby late Pleistocene Albemarle-Currituck slide, if it nucleated on the newly discovered crack system. Toward this goal, a tsunami scenario is constructed for the nearby coastal zone based on the estimated volume and nature of the potential slide. Although a maximum tsunami height of a few to several meters is predicted, the actual extent of flooding would depend on the tidal state at the time of tsunami arrival as well as the details of the hinterland topography. The VirginiaâNorth Carolina coastline and lower Chesapeake Bay would be most at risk, being nearby, low lying, and in a direction opposite to potential slide motion.
Duncan, C. S., J. A. Goff, J. A. Austin, and C. S. Fulthorpe, Tracking the last sea level cycle: Seafloor morphology and shallow stratigraphy of the latest Quaternary New Jersey middle continental shelf, Marine Geol., 170, 395-421, 2000, 49 citations, doi:10.1016/S0025-3227(00)00082-7, #1505
Seafloor geomorphology and surficial stratigraphy of the New Jersey middle continental shelf provide a detailed record of sea-level change during the last advance and retreat of the Laurentide ice sheet (120 kyr B.P. to Present). A NWâSE-oriented corridor on the middle shelf between water depths of 40 m (the mid-shelf âpaleo-shoreâ) and 100 m (the Franklin âpaleo-shoreâ) encompasses 500 line-km of 2D Huntec boomer profiles (500â3500 Hz), an embedded 4.6 km2 3D volume, and a 490 km2 swath bathymetry map. We use these data to develop a relative stratigraphy. Core samples from published studies also provide some chronological and sedimentological constraints on the upper <5 m of the stratigraphic succession.
The following stratigraphic units and surfaces occur (from bottom to top): (1) âRâ, a high-amplitude reflection that separates sediment >46.5 kyr old (by AMS 14C dating) from overlying sediment wedges; (2) the outer shelf wedge, a marine unit up to 50 m thick that onlaps âRâ; (3) âChannelsâ, a reflection sub-parallel to the seafloor that incises âRâ, and appears as a dendritic system of channels in map view; (4) âChannelsâ fill, the upper portion of which is sampled and known to represent deepening-upward marine sediments 12.3 kyr in age; (5) the âTâ horizon, a seismically discontinuous surface that caps âChannelsâ fill; (6) oblique ridge deposits, coarse-grained shelly units comprised of km-scale, shallow shelf bedforms; and (7) ribbon-floored swales, bathymetric depressions parallel to modern shelf currents that truncate the oblique ridges and cut into surficial deposits.
We interpret this succession of features in light of a global eustatic sea-level curve and the consequent migration of the coastline across the middle shelf during the last 120 kyr. The morphology of the New Jersey middle shelf shows a discrete sequence of stratigraphic elements, and reflects the pulsed episodicity of the last sea-level cycle. âRâ is a complicated marine/non-marine erosional surface formed during the last regression, while the outer shelf wedge represents a shelf wedge emplaced during a minor glacial retreat before maximum Wisconsin lowstand (i.e., marine oxygen isotope stage 3.1). âChannelsâ is a widespread fluvial subarial erosion surface formed at the late Wisconsin glacial maximum 22 kyr B.P. The shoreline migrated back across the mid-shelf corridor non-uniformly during the period represented by âChannelsâ fill. Oblique ridges are relict features on the New Jersey middle shelf, while the ribbon-floored swales represent modern shelf erosion. There is no systematic relationship between modern seafloor morphology and the very shallowly buried stratigraphic succession.
Goff, J. A., Simulation of stratigraphic architecture fom statistical and geometrical characterizations, Mathematical Geol., 32, 765-786, 2000, 1 citation, doi:10.1023/A:1007579922670, #1450
Stratigraphic modeling based on physical and geologic principles has been improved by more sophisticated process models and increased computer power. However, such efforts may reach a limit in their predictive power because of the stochastic, multiscaled nature of the physical processes involved. Building on techniques from the geostatistical literature, a conditional simulation method, dubbed SimStrat, has been developed to improve predictions of stratigraphic architecture from limited data. No physical processes are invoked. Rather, the prediction is based solely on geometric and statistical principals. The method takes as input sonar bathymetry, seismically defined stratigraphic horizons, and core-defined horizons. Each stratigraphic horizon is characterized using spectral modeling and coherence modeling for adjacent horizons. Predictions of subsurface horizons are improved where seafloor bathymetry conforms with the underlying strata. Conditional simulations can then be generated that conform to available data constraints and statistical characterization. Tests with synthetic data in one and two dimensions for differing spectral models confirm the reliability of the method.
Goff, J. A., H. C. Olson, and C. S. Duncan, Correlation of side-scan backscatter intensity with grain-size distribution of shelf sediments, New Jersey margin, Geo-Marine Lett., 20, 43-49, 2000, 44 citations, doi:10.1007/s003670000032, #1499
The dependence of acoustic backscatter variations on sediment grain-size distribution is examined using a combined analysis of 95 kHz side-scan data and approx. 300 grab samples from the New Jersey margin. We show that, under well-controlled circumstances, an unprecedented degree of correlation can be obtained between backscatter intensity and mean grain size. However, backscatter is disproportionately affected by larger grain sizes. Addition of just a few extra weight percentage of the larger grain sizes (>4 mm), which in our study is typically represented by more abundant shell hash among the older sediments at greater water depths, can completely degrade this correlation.
Goff, J. A., How sick is the Spring AGU meeting?, Eos, Trans. Amer. Geophys. Un., 81, 563, 2000, #1562
Borgeld, J. C., J. E. Hughes-Clarke, J. A. Goff, L. A. Mayer, and J. A. Curtis, Acoustic backscatter of the 1995 flood deposit on the Eel shelf, Marine Geol., 154, 197-210, 1999, 39 citations, doi:10.1016/S0025-3227(98)00113-3, #1361
Acoustic swath mapping and sediment box coring conducted on the continental shelf near the mouth of the Eel River revealed regional variations in acoustic backscatter that can be related to the shelf sedimentology. The acoustic-backscatter variations observed on the shelf were unusually narrow compared to the response of similar sediment types documented in other areas. However, the acoustic data revealed four principal bottom types on the shelf that can be related to sedimentologic differences observed in cores. The four areas are: (1) low acoustic backscatter associated with the nearshore-sand facies and the prodelta terraces of the Eel and Mad rivers, composed of fine sands and coarse silts with low porosity; (2) high acoustic backscatter associated with fine silts characterized by high porosity and deposited by the 1995 flood of the Eel River; (3) intermediate acoustic backscatter in the outer-shelf muds, where clayey silts are accumulating and the 1995 flood apparently had limited direct effect; and (4) intermediate acoustic backscatter near the fringes of the 1995 flood deposits and in areas where the flood sediments were more disrupted by post-depositional processes. The highest acoustic backscatter was identified in areas where the 1995 flood sediments remained relatively intact and near the shelf surface into the summer of 1995. Cores collected from these areas contained wavy or lenticular bedding. The rapid deposition of the high-porosity muddy layers results in better preservation of incorporated ripple forms than in areas less directly impacted by the flood deposit. The high-porosity muddy layers allow acoustic penetration into the sediments and result in greater acoustic backscatter from incorporated roughness elements.
Goff, J. A., D. L. Orange, L. A. Mayer, and J. E. Hughes-Clarke, Detailed investigation of continental shelf morphology using a high-resolution swath sonar survey: The Eel margin, northern California, Marine Geol., 154, 255-269, 1999, 59 citations, doi:10.1016/S0025-3227(98)00117-0, #1287
The Eel shelf, northern California, lies within an active compressional tectonic margin subject to abundant terrigenous sediment input from the Eel River. A recent high-resolution swath sonar survey provides us with the opportunity to investigate seafloor morphology and acoustic backscatter patterns within this dynamic region. Our analysis of the statistical character of bathymetry demonstrates a clear separation into large- and small-scale morphologies at a 3â10 km scale, with smaller-scale morphology heavily damped relative to large-scale morphology. The Eel shelf bathymetry is subtle, but several structures can be readily discerned in a residual bathymetry formed by removal of the downslope gradient. Some shelf structures are evidently related to depositional processes (as evidenced by correlation with 100-yr sediment accumulation rates), whereas others appear related to tectonic processes (as evidenced by correlation with subsurface synclines and anticlines). The sidescan structure of the shelf is dominated by the low backscatter over the Eel and Mad River subaqueous deltas, evidently associated with the sand-to-mud transition. However, contrary to usual correlations between backscatter and grain size, in this situation higher backscatter is associated with the muddy sediments. In addition, we observe a series of shore-perpendicular striations, or âribbons', spaced 0.2â1.0 km apart, which extend northward from the Eel River subaqueous delta and lie at or near the sand-to-mud transition. Some aspects of ribbon morphology suggest that they may be associated with down-slope flows.
Goff, J. A., and J. W. Jennings, Improvement of Fourier-based unconditional and conditional simulations for band limited fractal (von Karman) statistical models, Mathematical Geol., 31, 627-649, 1999, 12 citations, doi:10.1023/A:1007524209849, #1397
We evaluate the performance and statistical accuracy of the fast Fourier transform method for unconditional and conditional simulation. The method is applied under difficult but realistic circumstances of a large field (1001 by 1001 points) with abundant conditioning criteria and a band limited, anisotropic, fractal-based statistical characterization (the von Kármán model). The simple Fourier unconditional simulation is conducted by Fourier transform of the amplitude spectrum model, sampled on a discrete grid, multiplied by a random phase spectrum. Although computationally efficient, this method failed to adequately match the intended statistical model at small scales because of sinc-function convolution. Attempts to alleviate this problem through the covariance method (computing the amplitude spectrum by taking the square root of the discrete Fourier transform of the covariance function) created artifacts and spurious high wavenumber content. A modified Fourier method, consisting of pre-aliasing the wavenumber spectrum, satisfactorily remedies sinc smoothing. Conditional simulations using Fourier-based methods require several processing stages, including a smooth interpolation of the differential between conditioning data and an unconditional simulation. Although kriging is the ideal method for this step, it can take prohibitively long where the number of conditions is large. Here we develop a fast, approximate kriging methodology, consisting of coarse kriging followed by faster methods of interpolation. Though less accurate than full kriging, this fast kriging does not produce visually evident artifacts or adversely affect the a posteriori statistics of the Fourier conditional simulation.
Goff, J. A., and K. Holliger, Nature and origin of upper crustal seismic velocity fluctuations and associated scaling properties: Combined stochastic analyses of KTB velocity and lithology logs, J. Geophys. Res., 104, 13169-13182, 1999, 36 citations, #1421
The main borehole of the German Continental Deep Drilling Program (KTB) extends over 9000 m into a crystalline upper crust consisting primarily of interlayered gneiss and metabasite. We present a joint analysis of the velocity and lithology logs in an effort to extract the lithology component of the velocity log. Covariance analysis of lithology log, approximated as a binary series, indicates that it may originate from the superposition of two Brownian stochastic processes (fractal dimension 1.5) with characteristic scales of ∼2800 m and ∼150 m, respectively. Covariance analysis of the velocity fluctuations provides evidence for the superposition of four stochastic process with distinct characteristic scales. The largest two scales are identical to those derived from the lithology, confirming that these scales of velocity heterogeneity are caused by lithology variations. The third characteristic scale, ∼20 m, also a Brownian process, is probably related to fracturing based on correlation with the resistivity log. The superposition of these three Brownian processes closely mimics the commonly observed l/k decay (fractal dimension 2.0) of the velocity power spectrum. The smallest scale process (characteristic scale ∼1.7 m) requires a low fractal dimension, ∼1.0, and accounts for ∼60% of the total rms velocity variation. A comparison of successive logs from 6900â7140 m depth indicates that such variations are not repeatable and thus probably do not represent true velocity variations in the crust. The results of this study resolve disparity between the differing published estimates of seismic heterogeneity based on the KTB sonic logs, and bridge the gap between estimates of crustal heterogeneity from geologic maps and borehole logs.
Goff, J. A., D. J. P. Swift, C. S. Duncan, L. A. Mayer, and J. E. Hughes-Clarke, High-resolution swath sonar investigation of sand ridge, dune and ribbon morphology in the offshore environment of the New Jersey margin, Marine Geol., 161, 307-337, 1999, 47 citations, doi:10.1016/S0025-3227(99)00073-0, #1437
Sand ridges on the northeast US Atlantic shelf form in the near-shore environment, most likely in response to storm-driven flows. As the Holocene transgression has continued, the ridges have been transferred to an offshore hydrodynamic regime, where currents are not constrained by the coast and storms do not influence bottom currents as frequently or as strongly. Here, we qualitatively and quantitatively investigate the morphology of offshore sand ridges and smaller-scale features in an effort to place constraints on bedform development in these deeper waters. A recent high-resolution swath sonar survey mapped a portion of the New Jersey shelf from 20 m water depth to the shelf break (120 m), imaging both sand ridges and smaller-scaled dunes and ribbons in far greater detail than has been previously possible. Using a robust statistical analysis, we find that the gross morphology of ridges (height, width, length) does not change with depth beyond 20 m water depth, and changes in ridge orientation generally mirror changes in regional contour orientation. Hence, ridges have not continued to grow since transgression has brought them into the offshore hydrodynamic regime. However, on the inner shelf (20 m water depth to the Mid-Shelf shore), we do find evidence in the ridge shape, which has an asymmetry opposite to that seen near shore, and in the complex backscatter response that some important modifications to ridges are taking place at these water depths. In contrast, on the mid-shelf (from the Mid-Shelf shore to the Franklin shore), ridges tend to have higher backscatter at the crests, implying that these are largely winnowed, relict features. Lineated, smaller-scale (100â500 m wavelength, <1 m rms height) features are also present in the seafloor morphology. On the inner shelf these are North-trending, and are evidently transverse to an onshore-directed flow (dunes), whereas on the mid shelf these are NE/SW-trending and are parallel to a SW-directed flow (ribbons). The inner shelf dunes frequently exist on the seaward flanks of ridges, whereas the mid-shelf ribbons only inhabit large NE/SW-oriented swales between clusters of ENE-trending ridges. Morphologic and seismic evidence suggests that the ribbon-floored swales represent erosional intrusions into the otherwise relict ridge morphology. Also present on the mid-shelf are asymmetric blow-out pits and transverse dune packets, both of which are consistent with a SW-directed flow. Relict iceberg scours are present on the outer shelf Hudson Apron, evidently preserved by outcropping stiff clays, and are overlain in some places by ENE-trending ridges.
Goff, J. A., Finding chaos in abyssal hills, Nature, 392, 224-227, 1998, doi:10.1038/32524, #1386
Abyssal hills cover most of the Earth's sea floor. They are, in fact, the most common morphological feature on the Earth's surface, yet they are among the least understood.
Goff, J. A., Y. Ma, A. Shah, J. R. Cochran, and J.-C. Sempere, Stochastic analysis of seafloor morphology on the flank of the Southeast Indian Ridge: The influence of ridge morphology on the formation of abyssal hills, J. Geophys. Res., 102, 15521-15534, 1997, 28 citations, #1280
In this study we estimate the statistical properties of abyssal hill morphology adjacent to the Southeast Indian Ridge in a region where the axial morphology changes from axial high to axial valley without a corresponding change in spreading rate. We explore the influence of axial morphology on abyssal hills and place these results within the context of response to spreading rate. Two cruises aboard the R/V Melville collected Sea Beam 2000 multibeam data along the Southeast Indian Ridge, providing continuous multibeam coverage of the axis from ∼89°W to ∼118°W, and ∼100% coverage within four survey regions extending out to ∼45 km (∼1.2 Ma) from the axis [Sempéré et al., 1997; Cochran et al., 1997]. We apply the statistical modeling method of Goff and Jordan [1988] to gridded data from the four survey areas, examining in particular estimates of abyssal hill rms height, characteristic width and length, aspect ratio, and skewness. Two analyses are performed: (1) comparison of the along-axis variation in abyssal hill characteristics to ridge segmentation, and (2) a calculation of population statistics within axial high, intermediate, and axial valley data populations of this study, and comparison of these results to population statistics derived from studies adjacent to the Mid-Atlantic Ridge and East Pacific Rise. We find that abyssal hills generated along axial high mid-ocean ridges are very different from those generated along axial valley mid-ocean ridges, not only with respect to size and shape, but also in their response to such factors as spreading rate and segmentation.
Goff, J. A., and B. E. Tucholke, Multiscale spectral analysis of bathymetery on the flank of the Mid-Atlantic Ridge: Modification of the seafoor by mass wasting and sedimentation, J. Geophys. Res., 102, 15447-15462, 1997, 15 citations, #1281
The results of a multiscale spectral analysis of bathymetric data on the flank of the Mid-Atlantic Ridge are described. Data were collected during two cruises using Hydrosweep multibeam (tens of kilometers to ∼0.2 km scale range) and Mesotech scanning pencil-beam sonar attached to remotely operated vehicle Jason (∼1 km to ∼0.5 m scale range). These data are augmented by visual data which enabled us to identify bathymetric profiles which are over unsedimented or thinly sedimented crust. Our analysis, therefore, is focused primarily on statistical characterization of basement morphology. Work is concentrated at two sites: site B on ∼24 Ma crust in an outside-corner setting, and site D on ∼3 Ma crust in an inside-corner setting. At site B we find that an anisotropic, band-limited fractal model (i.e., the âvon Kármánâ model proposed for abyssal hill morphology by Goff and Jordan [1988]) is not sufficient to describe the full range of scales observed in this study. Our observations differ from this model in two ways: (1) strike and cross-strike (dip) spectral properties converge for wavelengths smaller than ∼300 m, and (2) in both strike and dip directions the fractal dimension changes at ∼10 m wavelength, from ∼1.27 at larger scales to ∼1.0 at smaller scales. The convergence of strike and dip spectral properties appears to be associated with destruction of ridge-parallel fault scarps by mass wasting, which develops canyon-like incisions that cross scarps at high angles. The change in fractal dimension at ∼10 m scale appears to be related to a minimum spacing of significant slope breaks associated with scarps which are created by faulting and mass wasting. At site D, although there is no significant abyssal hill anisotropy, the spectral properties at all scales are consistent with the von Kármán model. The fractal dimension at this site (∼1.15) is less than at site B. This difference may be reflect different morphology related to crustal formation at inside-corner versus outside-corner position or, more likely, differences in the degree of mass wasting. The smoothing of seafloor morphology by sediments is evident in Hydrosweep periodograms where, relative to basement roughness, spectral power decreases progressively with decreasing wavelength.
Lendl, C., A. M. Trehu, J. A. Goff, A. R. Levander, and B. C. Beaudoin, Synthetic seismograms through synthetic Franciscan: Insights into factors affecting large-aperture seismic data, Geophys. Res. Lett., 24, 3317-3320, 1997, 7 citations, #1360
In spite of an order of magnitude increase over the past 15 years in spatial sampling of the wavefield, a major uncertainty in the analysis of active source seismic data remains phase identification. This uncertainty results in part from the wide range of spatial scales of velocity heterogeneity in the crust. Smaller scale variations than those which can be deterministically resolved given the design of a particular seismic experiment can be modeled statistically using geologic constraints. Here we present synthetic seismograms generated from several different realizations of a stochastic model describing the velocity heterogeneity of Franciscan terrane rocks. We compare the results to observed data and to synthetic seismograms generated for a model derived from tomographic inversion of the data in order to obtain qualitative insights into the relative importance of large and small scale velocity heterogeneity. Not surprisingly, the synthetic data for the tomographic model best reproduce observed small‐scale variations in first arrival time, which only occur for particular realizations of the stochastic model. The synthetic seismograms generated for the stochastic models best reproduce the level of signal‐generated noise and suggest that the amplitude of velocity variation locally within the Franciscan is approximately 1 km/s. They also illustrate the effect of a strongly heterogeneous upper and mid‐crust on the amplitude‐versus‐offset pattern of arrivals from the lower crust and upper mantle. These effects may sometimes be interpreted deterministically, leading to biased models or an overly optimistic estimate of lower crustal resolution.
Tucholke, B. E., J. Lin, M. C. Kleinrock, M. Tivey, T. Reed, J. A. Goff, and G. E. Jaroslow, Segmentation and crustal structure of the western Mid-Atlantic Ridge flank, 25° 25'-27° 10' and 0-29 m.y., J. Geophys. Res., 102, 10203-10223, 1997, 74 citations, #1380
We conducted a detailed geological-geophysical survey of the west flank of the Mid-Atlantic Ridge between 25°25′N and 27°10′N and from the ridge axis out to 29 Ma crust, acquiring Hydrosweep multibeam bathymetry, HAWAII MR1 sidescan-sonar imagery, gravity, magnetics, and single-channel seismic reflection profiles. The survey covered all or part of nine spreading segments bounded by mostly nontransform, right-stepping discontinuities which are subparallel to flow lines but which migrated independently of one another. Some discontinuities alternated between small right- and left-stepping offsets or exhibited zero offset for up to 3â4 m.y. Despite these changes, the spreading segments have been long-lived and extend 20 m.y. or more across isochrons. A large shift (∼9°) in relative plate motion about 24â22 Ma caused significant changes in segmentation pattern. The nature of this plate-boundary response, together with the persistence of segments through periods of zero offset at their bounding discontinuities, suggest that the position and longevity of segments are controlled primarily by the subaxial position of buoyant mantle diapirs or focused zones of rising melt. Within segments, there are distinct differences in seafloor depth, morphology, residual mantle Bouguer gravity anomaly, and apparent crustal thickness between inside-corner and outside-corner crust. This demands fundamentally asymmetric crustal accretion and extension across the ridge axis, which we attribute to low-angle, detachment faulting near segment ends. Cyclic variations in residual gravity over the crossisochron run of segments also suggest crustal-thickness changes of at least 1â2 km every 2â3 m.y. These are interpreted to be caused by episodes of magmatic versus relatively amagmatic extension, controlled by retention and quasiperiodic release of melt from the upwelling mantle. Detachment faulting appears to be especially effective in exhuming lower crust to upper mantle at inside corners during relatively amagmatic episodes, creating crustal domes analogous to âturtlebackâ metamorphic core complexes that are formed by low-angle, detachment faulting in subaerial extensional environments.
Goff, J. A., and A. R. Levander, Incorporating "sinuous connectivity" into stochastic models of crustal heterogeneity: Examples from the Lewisian gneiss complex, Scotland, the Franciscan formation, California, and the Hafafit gneiss complex, Egypt, J. Geophys. Res., 101, 8489-8501, 1996, 16 citations, #1185
Stochastic models are valuable and sometimes essential tools for investigating the behavior of complex phenomena. In seismology, stochastic models can be used to describe velocity heterogeneities that are too small or too numerous to be described deterministically. Where analytic approaches are often infeasible, synthetic realizations of such models can be used in conjunction with finite difference algorithms to systematically investigate the response of the seismic wave field to complex heterogeneity. This paper represents a continuing effort at formulating a complete and robust stochastic model of lithologic heterogeneity within the crust, and the means of generating synthetic realizations; âcompleteâ implies that the model is flexible enough to describe all types of random heterogeneity within the crust, while ârobustâ implies sufficiently constrained parameterization that an inversion problem may be well-posed. As a basis for investigation we use geologic maps of crustal exposures and petrophysically inferred velocities. Earlier efforts at stochastic modeling have focused on characterization of the univariate probability density function, which is typically modal (i.e., binary, ternary, etc.), and the covariance function, which is typically fit with a von Kármán function. Here we provide a means of characterizing the property of âsinuous connectivityâ and for generating realizations that possess this property. Sinuous connectivity is the tendency for individual lithologic units to be continuous over long and highly contorted paths; there is no means in the earlier modeling of either characterizing or synthesizing this property. We generate sinuously connective realizations by mapping regions encompassed by two contours in a Gaussian-distributed surface into the two values of the binary field. This operation is nonunique, as one can choose, in many ways, the values for the contours.
Goff, J. A., and J. R. Cochran, The Bauer Scarp ridge jump: A complex tectonic sequence revealed in satellite altimetry, Earth Planet. Sci. Lett., 141, 21-33, 1996, 19 citations, doi:10.1016/0012-821X(96)00061-1, #1221
We investigate here the ridge jump that led to abandonment of the Galapagos Rise and formation of the Bauer scarp during the initiation of the present day configuration of the East Pacific Rise since the lower Miocene. We use recently available high resolution satellite-derived gravity data to investigate in detail the tectonic structure of the eastern Pacific from the Equator to 20°S. With this data, we identify fracture zones, abandoned spreading ridges, scarps, and other seafloor features that provide evidence for discerning tectonic history.
Based on our structural interpretation of the satellite-derived gravity field, we make the following conclusions: (1) The Galapagos Rise spreading center appears to have originated by opening of the Marquesas/Mendaña transform complex as a result of the change in spreading direction following breakup of the Farallon Plate. (2) The Galapagos Rise was not the sole locus of spreading following plate reorganization at 20 Ma through to the initiation of the Bauer scarp at 8 Ma, as had been previously hypothesized. Rather, it and a second western spreading axis were likely active concurrently, forming a counterclockwise-rotating Bauer Microplate at a much earlier stage than thought previously. (3) The Bauer scarps are pseudofaults associated with northward rift propagation. Propagation proceeded in several stages. A first propagator emanating from the Garrett transform complex stalled at the future location of the Wilkes transform creating an area of complex morphology near its northern tip. A second propagator, also emanating from the Garrett complex followed in the first's wake and broke through the complex region. At this point the propagation proceeded very rapidly to the northern end of the Bauer Microplate (the Gallego fracture zone, later to become the Yaquina transform fault). Ridge propagation continued north in two more stages, creating the Gofar and Quebrada transforms at the terminus of each stage.
Goff, J. A., L. A. Mayer, J. E. Hughes-Clarke, and L. F. Pratson, Swath mapping on the continental shelf and slope: The Eel River Basin, northern California, Oceanography, 9 (3), 178-182, 1996, #1232
Larkin, S. P., A. R. Levander, D. Okaya, and J. A. Goff, A deterministic and stochastic velocity model for the Salton Trough/Basin and Range transition zone and constraints on magmatism during rifting, J. Geophys. Res., 101, 27883-27897, 1996, 6 citations, #2145
As a high resolution addition to the 1992 Pacific to Arizona Crustal Experiment (PACE), a 45-km-long deep crustal seismic reflection profile was acquired across the Chocolate Mountains in southeastern California to illuminate crustal structure in the transition between the Salton Trough and the Basin and Range province. The complex seismic data are analyzed for both large-scale (deterministic) and fine-scale (stochastic) crustal features. A low-fold near-offset common-midpoint (CMP) stacked section shows the northeastward lateral extent of a high-velocity lower crustal body which is centered beneath the Salton Trough. Off-end shots record a high-amplitude diffraction from the point where the high velocity löwer crust pinches out at the Moho. Above the high-velocity lower crust, moderate-amplitude reflections occur at midcrustal levels. These reflections display the coherency and frequency characteristics of reflections backscattered from a heterogeneous velocity field, which we model as horizontal intrusions with a von Kármán (fractal) distribution. The effects of upper crustal scattering are included by combining the mapped surface geology and laboratory measurements of exposed rocks within the Chocolate Mountains to reproduce the upper crustal velocity heterogeneity in our crustal velocity model. Viscoelastic finite difference simulations indicate that the volume of mafic material within the reflective zone necessary to produce the observed backscatter is about 5%. The presence of wavelength-scale heterogeneity within the near-surface, upper, and middle crust also produces a 0.5-s-thick zone of discontinuous reflections from a crust-mantle interface which is actually a first-order discontinuity.
Steckler, M. S., D. J. P. Swift, J. P. M. Syvitski, J. A. Goff, and A. W. Niedoroda, Modeling the sedimentology and stratigraphy of continental margins, Oceanography, 9 (3), 183-188, 1996, #1359
Goff, J. A., Quantitative analysis of sea ice draft: 1. Methods for stochastic modeling, J. Geophys. Res., 100, 6993-7004, 1995, 9 citations, #1058
This paper seeks to develop a robust set of tools for estimating the stochastic properties of sea ice drafts. Five parameters are estimated, along with their formal uncertainties: mean draft, rms topographic variation, characteristic length, fractal dimension, and normalized skewness. These provide an objective basis for terrain classification. A recent 10-km by 10-km upward looking submarine sonar survey serves as a test case. Data profiles are compared with synthetic profiles generated from the statistical parameters estimated from the data. These provide a means of qualitatively assessing the success of the stochastic model at characterizing the principal morphological properties. In general, the comparisons are good, providing confidence in the applicability and versatility of the stochastic model. A few exceptions are notable, but these also provide valuable insight into our understanding of the morphology of sea ice draft.
Goff, J. A., W. K. Stewart, H. Singh, and X. Tang, Quantitative analysis of sea ice draft: 2. Application of stochastic modeling to intersecting topographic profiles, J. Geophys. Res., 100, 7005-7017, 1995, 4 citations, #1059
A recent upward looking sonar profile survey of a ∼10-km by 10-km area beneath the Arctic ice serves as a basis for an exploratory analysis of the quantitative characteristics of sea ice draft. In a companion paper (Goff, this issue) a method was developed for estimating profile statistical parameters and their uncertainties. These include mean draft, rms variation, characteristic length, fractal dimension, and normalized skewness. Here this methodology is applied to the intersecting profile data set, yielding 160 separate estimates for each parameter. Although not completely two-dimensional, the data nevertheless allow an opportunity to investigate some aspects of topographic anisotropy. Our most significant observations are (1) a strong positive correlation exists between fractal dimension and characteristic length, while normalized skewness is weakly negatively correlated with both parameters; (2) high and low rms/mean ice are morphologically distinct in the rms versus characteristic length and fractal dimension versus characteristic length parameter spaces; (3) the overall correlation between rms and characteristic length can be explained entirely by the difference between high and low rms/mean type morphology; and (4) anisotropy appears to exist on a local scale but is highly variable over the entire survey. These observations could be explained by a systematic variation in morphology with age, perhaps including a progressive superposition of deformation events, and/or by regionally variable anisotropy.
Goff, J. A., The relationship between local- and global-scale scattering functions for fractal surfaces under a separation of scales hypothesis, J. Acoustical Soc. Amer., 97, 1586-1595, 1995, 3 citations, doi:10.1121/1.412097, #1078
A ``separation of scales hypothesis'' is an important component of both composite roughness and facet scattering theories applied to fractal (i.e., realistic) surfaces. It asserts that a scattering surface is separated by the acoustic wavelength into two scale regimes; features larger than the acoustically defined ``separation scale'' act to reflect rays specularly, whereas features smaller than the separation scale act to scatter acoustic energy diffusely. This paper explores the consequences of this hypothesis by formulating the relationship between an arbitrary local-scale scattering strength function, describing the diffuse component of scattering relative to a local-scale slope, and three global-scale scattering strength functions, which describe scattering over the entire surface relative to the horizontal. These include: mean and rms scattering strength, and grain ratio scattering strength (the ratio of scattering strength from two principal directions of an anisotropic surface). Each provides an important independent constraint on the relationship between local- and global-scale scattering properties: (1) Mean global-scale scattering strength is essentially a more diffuse version of local-scale scattering strength; (2) rms global-scale scattering strength exhibits great sensitivity at low grazing angles to the local-scale scattering strength model; and (3) grain ratio scattering strength is sensitive to the functional form of local-scale scattering strength, especially at low grazing angles. Examples demonstrate that sinusoidal local-scale scattering produces sinusoidal global-scale scattering, whereas Lambertian local-scale scattering does not result in Lambertian global-scale scattering.
Goff, J. A., B. E. Tucholke, J. Lin, G. E. Jaroslow, and M. C. Kleinrock, Quantitative analysis of abyssal hills in the Atlantic Ocean: A correlation between inferred crustal thickness and extensional faulting, J. Geophys. Res., 100, 22509-22522, 1995, 25 citations, #1154
A recent cruise to the Office of Naval Research Atlantic Natural Laboratory obtained ∼100% Hydrosweep bathymetrie coverage, >200% Hawaii MRl (HMRl) side scan coverage, gravity and magnetics over an area spanning three ridge segments along axis (∼25°25′N to ∼27°10′N), and crustal ages from 0 to 26â30 Ma (∼400 km) on the west flank of the Mid-Atlantic Ridge. This data set represents a first opportunity for an extensive regional analysis of abyssal hill morphology created at a slow spreading ridge. The primary purpose of this work is to investigate the relationship between abyssal hill morphology and the properties of the ridge crest at which they were formed. We apply the method of Goff and Jordan [1988] for the estimation of two-dimensional statistical properties of abyssal hill morphology from the gridded Hydrosweep bathymetry. Important abyssal hill parameters derived from this analysis include root-mean-square (rms) height, characteristic width, and plan view aspect ratio. The analysis is partitioned into two substudies: (1) analysis of near-axis (< 7 Ma) abyssal hills for each of the three segments and (2) analysis of temporal variations (∼2â29 Ma) in abyssal hill morphology along the run of the south segment. The results of this analysis are compared and correlated with analysis of the gravity data and preliminary determination of faulting characteristics based on HMRl side scan data. Principal results of this study are: (1) Abyssal hill morphology within the study region is strongly influenced by the inside-outside corner geometry of the mid-ocean ridge segments; abyssal hills originating at inside corners have larger rms height and characteristic width and smaller plan view aspect ratio than those originating at outside corners. (2) The residual mantle Bouguer gravity anomaly is positively correlated with intersegment and along-flow-line variations in rms height and characteristic width, and it is negatively correlated with plan view aspect ratio. From this result, we infer that lower-relief, narrower, and more elongated abyssal hills are produced when the crust being generated is thicker. (3) Intersegment variations in near-axis rms height negatively correlate with average fault density as determined from analysis of HMRl side scan imagery.
Goff, J. A., K. Holliger, and A. R. Levander, Modal fields: A new method for characterization of random seismic velocity heterogeneity, Geophys. Res. Lett., 21, 493-496, 1994, 45 citations, #1044
Geologically and petrophysically constrained synthetic random velocity fields are important tools for exploring (through the application of numerical codes) the seismic response of small‐scale lithospheric heterogeneities. Statistical and geophysical analysis of mid‐ and lower‐crustal exposures has demonstrated that the probability density function for some seismic velocity fields is likely to be discrete rather than continuous. We apply the term âmodalâ fields to describe fields of this sort. This letter details a methodology for generating synthetic modal fields which satisfy the von Kármán covariance function. In addition, we explore some of the mathematics of âmodalityâ, and define a modality parameter which quantifies the variation between end members binary and continuous fields.
Levander, A. R., R. W. England, S. K. Smith, R. W. Hobbs, J. A. Goff, and K. Holliger, Stochastic characterization and seismic response of upper and middle crustal rocks based on the Lewisian gneiss complex, Scotland, Geophys. J. Int., 119, 243-259, 1994, 27 citations, doi:10.1111/j.1365-246X.1994.tb00925.x, #1358
We have developed statistical models of upper and middle crustal seismic velocity heterogeneity based on geologic maps and petrophysical data from the Lewisian gneiss complex, Scotland. the level of heterogeneity we have measured is relevant to seismic exploration of the crystalline crust using conventional reflection and refraction techniques. We digitized two 1:10560 geologic maps of Laxfordian (Archean) age Lewisian rocks on a 26.8m grid. Both maps are believed to be representative of the upper and middle crust in north-western Scotland, and both are believed to provide cross-sectional views of parts of the crust. the digital maps were characterized by the statistics of their lithologic populations and by their 2-D spatial autocorrelation functions. Different lithologies were assigned seismic velocities appropriate for the mid-crust using petrophysical data. Three lithologies are dominant: silicic gneisses (Vp∼6.2 km s−1), mafic amphibolites (Vpâ 6.75 kms−1), and intermediate composition schists (Vpâ6.5kms−1). Both maps have self-affine spatial fabrics.
The first map covers the core of a syncline. Its autocorrelation function defines a medium with a fractal dimension of 2.78, a horizontal characteristic length of about 244m and a vertical correlation of about 133m (aspect ratio is 2:1). It has an essentially trimodal velocity (lithology) population consisting of 37 per cent silicicgneiss, 43 per cent mafic amphibolites, and 20 per cent schists. This map is representative of 30-40 per cent of Laxfordian rocks. the second map is a plan view which can be rotated 90° about an axis perpendicular to strike to give a cross-section. This map is characterized by a fractal dimension of 2.55, with a horizontal correlation length of about 111m and a vertical correlation of about 38m (aspect ratio 3:1). It has a nearly bimodal population consisting of 77 per cent silicic gneisses and 22 per cent mafic amphibotites. It is representative of 60-70 per cent of Laxfordian rocks.
Lastly we examine the seismic response of an upper to middle crust based on our statistical models using acoustic and elastic 2-D finite-difference synthetic seismograms. Short-offset shot records demonstrate that a Lewisian upper crust produces scattered waves which significantly disrupt signals reflecting from deeper levels. Measurements of transmission scattering Q, and coda decay rates confirm that seismic scattering in Lewisian-type crust is strong. the migrated CMP response of a Lewisian crustal model shows the characteristic 'salt and pepper' pattern often observed in the upper crust, and described, incorrectly, as 'transparent'. We suggest that 'translucent' is a more appropriate descriptor.
Macario, A., W. F. Haxby, J. A. Goff, W. B. F. Ryan, S. C. Cande, and C. A. Raymond, Flow line variations in abyssal hill morphology for the Pacific-Antarctic Ridge at 65°S, J. Geophys. Res., 99, 17921-17934, 1994, 20 citations, #1357
We present the results of a statistical study on the morphological characteristics of abyssal hills recently mapped along two adjacent segments of the Pacific-Antarctic Ridge at 65°S. The studied area is a densely surveyed corridor (60 km wide by 600 km long) which is centered on the Pitman Fracture Zone (PFZ) and extends to 12 Ma crust on both sides of the ridge. Abyssal hill size parameters (RMS height H and characteristic width λ) are estimated using Hydrosweep multibeam data. Variations in abyssal hill characteristics are compared with spreading rate history and crustal structure (as inferred from the mantle Bouguer gravity) in order to indirectly quantify the evolution of this ridge crest system. The magnetic data document an abrupt acceleration in spreading rate from ∼36 to ∼63 mm/yr (full rate) at Chron 3a (5.7â6.4 Ma). Our results indicate a statistically significant negative correlation between abyssal hill size parameters and full spreading rates. Abyssal hills formed during the slower spreading period (ages >8 Ma; full rates 36â44 mm/yr) are 31â86% taller and 21- >100% wider than hills created during the faster spreading interval (ages <4 Ma; full rates 52â63 mm/yr). The well-resolved positive correlation between H and λ is interpreted as an indication of temporal changes in the flexural rigidity of the lithosphere near the vicinity of the ridge crest and, by implication, axial thermal structure. However, we cannot rule out that such positive trend is due to constructional volcanism. The lack of correlation between crustal thickness and abyssal hill size parameters is likely to be caused by the small magnitude of crustal thickness variations along flow lines (∼0.4 km in contrast to ∼2 km reported in previous studies for the Mid-Atlantic Ridge). The most significant variations in crustal thickness are seen across the PFZ (thinning from north to south by 0.5â0.7 km), which coincide with a well-resolved increase in the averaged λ estimate. The predictions of the detachment surface model in terms of morphological and structural inside/outside comer asymmetries are not supported by our observations. The main variations in H and λ that cannot be explained in terms of either the spreading rate or crustal thickness effect include the following: (1) anomalously large abyssal hills north of the PFZ for 4â6 Ma age crust; (2) abyssal hill size estimates for crustal ages greater than 8 Ma show significant asymmetry for opposite ridge flanks north of the PFZ; and (3) toward the segment ends, H estimates are 27â68% larger, while λ estimates either do not significantly change (to the north of the PFZ) or are up to 40% smaller (to the south of the PFZ). We suggest that the H and λ changes seen toward the segment ends are related to either an increase in the amount of extension (without a corresponding increase in the strength of the lithosphere) or variations in the relative contribution of constructional volcanism to overall abyssal hill morphology.
Cochran, J. R., J. A. Goff, A. Malinverno, D. J. Fornari, C. Keeley, and X. Wang, Morphology of a 'superfast' mid-ocean ridge crest and flanks: The East Pacific Rise, 7-9S, Marine Geophysical Researches, 15, 65-75, 1993, 38 citations, doi:10.1007/BF01204152, #1355
Detailed bathymetric data from a Hydrosweep multibeam sonar survey of a 250 km-long portion of the superfast-spreading southern East Pacific Rise crest and flanks show that the along-axis variation in morphology and axial depth differs significantly from that observed at the fast-spreading northern East Pacific Rise. While the deep mantle upwelling pattern is similar under the northern and southern East Pacific Rise, our observations require that the connectivity of the shallow, subcrestal plumbing system be more efficient beneath the super-fast spreading southern East Pacific Rise than beneath the slower spreading northern East Pacific Rise.
Holliger, K., A. R. Levander, and J. A. Goff, Stochastic modeling of the reflective lower crust: Petrophysical and geological evidence from the Ivrea Zone (Northern Italy), J. Geophys. Res., 98, 11967-11980, 1993, 49 citations, #1356
Crustal-scale seismic wave equation modeling demonstrates that wavelength-scale velocity fluctuations can dominate the seismic response over a wide range of offsets and that a wide range of velocity distributions qualitatively can explain deep seismic data. This range can be narrowed by studying the detailed petrophysical and structural properties of middle and lower crustal exposures. The Ivrea Zone, in the Southern Alps, is a well-studied sliver of extended lower continental crust brought into its present upright position as a result of late Alpine lithospheric shortening. The high degree of structural and petrophysical complexity and in particular the limited exposure of the Ivrea Zone favor a statistical rather than deterministic approach to develop a two-dimensional crustal-scale seismic model. For this purpose we digitized two 1:25,000 geological maps from the central Ivrea Zone on a 60-m grid. We find that the Ivrea Zone is characterized by a bimodal velocity distribution, and a band-limited self-affine structure having a fractal dimension of 2.7, a characteristic horizontal scale of 500 to 1000 m, and an aspect ratio around 4.0. Assuming statistical stationarity, a realization of this stochastic model was used to develop synthetic seismograms typical of ââ¬ÅIvrea-typeââ¬Â lower continental crust. Our results indicate that (1) Ivrea-type lower crust can explain qualitatively commonly observed lower crustal reflectivity, (2) relatively minor changes in bulk composition and/or metamorphic grade may lead to dramatic changes in reflectivity, which cannot be explained by current generic models on the origin of lower crustal reflections, and (3) travel time interpretation of the synthetic wide-angle data may lead to erroneous large-scale velocity structures.