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Thomas H. Shipley Telephone 512-471-0430 direct office |
Marine Geology and Geophysics
Convergent margin processes, 3-D seismic reflection
methods, marine geology.
Recent Graphics
Three-dimensional reflection project off the Pacific coast of Costa Rica (Shipley et al., 1992, JGR 97, 4439-4459). The seafloor mound is a 100-m high mud volcano/diapir. The subsurface shows some fluid conduits extending through the slope sediments from the wedge but they are discontinuous. Diving found a seep communit on the seafloor (McAdoo et al., 1996, GRL 23, 883-886). Click figure for larger version.
Movie loop showing 3-D perspective of a region of the Barbados plate boundary fault (decollement) and overlying accretionary wedge. The multi-decade Deep-Sea and Ocean Drilling programs and 3-D seismic imaging provided a direct calibration of fluid flow at individual well sites (vertical black lines, red lines are density logs). Flow is not 2-D but is focused along a northeasterly trending relatively narrow zone of high porosity. In the seismic section at top, thrust faults (arrows) splaying off the decollement are highly reflective and occur only above the high-porosity sections of the main fault, suggesting leakage into the overlying wedge (after Bangs et al., 1999). An optional larger movie loop is downloadable (3 MB b3d.big.gif). It is best played with a quicktime MoviePlayer.
Ocean Drilling Program Site 808 in the Nankai Trough provided the basis for comparing fluid flow in a margin with significantly coarser grained sediments than Barbados (after Taira et al., 1991). The decollement here is also strongly reflective and appears to separate hydrological units above and below the main fault. In late 1999, an U.S.-Japan 3-D seismic survey was conducted and analyses similar to the Barbados program are underway. Additional ODP drilling in 2000 will calibrate the fluid history of this margin. This project may form the basis for the first integrated program into an active seismogenic portion of a subduction thrust fault. When processing is complete on the 3-D survey it should extend well down into the zone of seismicity (click figure for larger version).
Research Interests
I have a number of research interests that primarily
involve understanding the subduction processes occurring at converging
plate margins. Subduction zones are regions of the earth where one plate
passes beneath another creating earthquakes and spawning volcanic activity.
Mass transfer from one plate to the other often produces large deformed
sedimentary rock wedges. Much of my work has involved investigating the
deformation of these wedges and their spatial and temporal evolution.
The location of fluids and how they move through an accretionary wedge controls the distribution of low shear strength fault zones. Three-dimensional seismic studies combined with drilling and seafloor observations are letting us observe fluids and their movement through the deforming wedges. A 3-D seismic reflection data volume of the accretionary prism off Barbados was designed to seismically examine some of these issues. The seismic reflections image the low-angle detachment fault between the Caribbean and Atlantic and characterize spatial variations of fault zone properties. There is good seismic evidence for a heterogeneous fault plane of very high porosity (and thus probably low-strength) punctuated with areas of low porosity (and thus higher strength).
Current research is moving into deeper structural levels, into portions of faults that are seismogenic. In June-August, 1999, we completed a 3-D survey of the Nankai subduction zone off southwest Japan.
Professional Service
Co-convener, Marine Seismic Reflection Acquisition
for the Next Decade, NSF Workshop, October, 1999
Elected council member, University National Oceanographic
Laboratory Systems (1997-90)
Member of the U.S. Margins Steering Committee (1999-2002)
Member of JOIDES OPCOM (1999-2000)
Funded Research Projects
A 3-D Seismic Investigation of the Sediment-to-Rock
Transition and Its Relationship to Nankai Subduction Thrust Seismicity:
US-Japan Collaborative Program
Structure, Tectonics, and Sediment Flow into the Lesser Antilles Subduction Zone
Selected Publications
Christeson, G.L., McIntosh, K.D., Shipley, T.H.,
Flueh, E., Schulze, A., 1999 submitted, Structure of the Costa Rica convergent
margin, offshore Nicoya Peninsula, JGR.
Shipley, T.H., Bangs, N.L. and Henning, A.T., 1999 accepted, Sediment velocity estimation using iterative 3-D migrations of short offset seismic reflection data in deep water, Marine Geophysical Researches,
Bangs, N.L., Shipley, T.H., Moore, J.C., and Moore, G.F., 1999, Fluid accumulation and channeling along the northern Barbados Ridge Decollement Thrust, JGR, 104, 20399-20414.
Phinney, E.J., Mann, P., Coffin, M.F. and Shipley, T.H., 1999, Sequence stratigraphy, structure, and tectonic history of the southwestern Ontong Java Plateau adjacent to the North Solomon Trench and Solomon Island Arc, JGR, 104, 20449-20466.
Bangs, N. L., Shipley, T. H., and Moore, G. F., Elevated fluid pressure and fault zone dilation inferred from seismic models of the northern Barbados Ridge decollement, JGR, 101,627-642, 1996.
Shipley, T. H., G. F. Moore, N. L. Bangs, J. C. Moore, and P. L. Stoffa, Seismically inferred dilatancy distribution, northern Barbados Ridge decollement: Implications for fluid migration and fault strength, Geology, 22, 411-414, 1994.
Shipley, T.H., L. Abrams, Y. Lancelot, and R. Larson, Late Jurassic-Early Cretaceous oceanic crust, Mid-Cretaceous volcanic sequences of the Nauru Basin, Western Pacific, In Pringle, M., W. Sager, B. Sliter and S. Stein, (eds.), The Mesozoic Pacific: Geology, Tectonics, and Volcanism, Geophysical Mono. 77, 103-119, 1993.
Shipley, T.H., K. McIntosh, E. Silver, and P. Stoffa, Three dimensional seismic imaging of the Costa Rica Accretionary Prism: Structural diversity in a small volume of the lower slope, JGR, 97, 4,439-4,459, 1992.
Click here to see more publications.
