UTIG RESEARCH PROJECTS ARCHIVE

Stochastic Modeling of Abyssal Hill Morphology: New Seafloor Models Based on Analysis of Fine Scale Basement Topography and Separate Characterization of Tectonic and Volcanic Morphology

Principal Investigator: John A. Goff

Funded by: Office of Naval Research

Project Abstract

The primary goal of this work is to quantitatively characterize abyssal hill basement morphology sufficiently enough to allow accurate forward modeling of ARSRP (Acoustic Reverberation Special Research Project) bottom reverberation data. Statistical analysis of bathymetric data available from both the large- and small-scale ARSRP geophysical reconnaissance cruises will be used to modify the "Goff-Jordan" covariance model into a more general stochastic model of abyssal hill basement morphology valid over a wide range of scales (~1m to ~100km). In addition, backscatter-based geologic classification available from HMR1 and AMS-120 side scan data will be used to separately characterize the faulted, volcanic, and possibly talus contributions to abyssal hill morphology. Both efforts are expected to lead to more realistic and accurate seafloor models for use as input into numerical acoustic reverberation experiments to be conducted by other ARSRP participants.

Recent Published Manuscript:

Goff, J. A., and B. E. Tucholke, Multi-scale spectral analysis of bathymetry on the flank of the Mid-Atlantic Ridge: Modification of the seafloor by mass wasting and sedimentation, J. Geophys. Res., 102, 15,447-15,462, 1997

Abstract This paper describes the results of a multi-scale spectral analysis of bathymetric data on the flank of the Mid-Atlantic Ridge. Data were collected during two cruises using Hydrosweep multibeam (10's of km to ~0.2 km scale range) and Mesotech scanning pencil-beam sonar attached to ROV 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 "von Karman" 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 Karman 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- 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.

Key Figure:

New conceptual model for the abyssal-hill basement power spectrum. Convergence of dip and strike spectra is likely associated with mass wasting destruction of axis-parallel fault scarps. Steepening of spectrum at highest wavenumbers is likely associated with minimum spacing of fault and mass wasting scarps.