Seismically inferred dilatancy distribution, northern Barbados Ridge decollement: Implications for fluid migration and fault strength

Abstract

Research Article| May 01, 1994 Seismically inferred dilatancy distribution, northern Barbados Ridge decollement: Implications for fluid migration and fault strength Thomas H. Shipley; Thomas H. Shipley 1Institute for Geophysics, University of Texas, Austin, Texas 78759 Search for other works by this author on: GSW Google Scholar Gregory F. Moore; Gregory F. Moore 2Department of Geology and Geophysics, University of Hawaii, Honolulu, Hawaii 96822 Search for other works by this author on: GSW Google Scholar Nathan L. Bangs; Nathan L. Bangs 1Institute for Geophysics, University of Texas, Austin, Texas 78759 Search for other works by this author on: GSW Google Scholar J. Casey Moore; J. Casey Moore 3Earth Sciences, University of California, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar Paul L. Stoffa Paul L. Stoffa 1Institute for Geophysics, University of Texas, Austin, Texas 78759 Search for other works by this author on: GSW Google Scholar Author and Article Information Thomas H. Shipley 1Institute for Geophysics, University of Texas, Austin, Texas 78759 Gregory F. Moore 2Department of Geology and Geophysics, University of Hawaii, Honolulu, Hawaii 96822 Nathan L. Bangs 1Institute for Geophysics, University of Texas, Austin, Texas 78759 J. Casey Moore 3Earth Sciences, University of California, Santa Cruz, California 95064 Paul L. Stoffa 1Institute for Geophysics, University of Texas, Austin, Texas 78759 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1994) 22 (5): 411–414. https://doi.org/10.1130/0091-7613(1994)022<0411:SIDDNB>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Thomas H. Shipley, Gregory F. Moore, Nathan L. Bangs, J. Casey Moore, Paul L. Stoffa; Seismically inferred dilatancy distribution, northern Barbados Ridge decollement: Implications for fluid migration and fault strength. Geology 1994;; 22 (5): 411–414. doi: https://doi.org/10.1130/0091-7613(1994)022<0411:SIDDNB>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A 5 x 25 km, three-dimensional seismic survey of the lower part of the northern Barbados Ridge accretionary prism creates a three-dimensional image of a major active decollement fault. The fault is usually a compound negative-polarity reflection modeled as a low-velocity, high-porosity zone less than ∼14 m thick. This thickness is significantly less than that defined by drilling of a >40 m zone of deformation at Ocean Drilling Program (ODP) Site 671B, located within the surveyed area. We infer that the seismically defined fault is a thin, high-porosity zone and is thus an undercompacted, high-fluid-pressure dilatant section. If these inferences are correct, then map-view variations in seismic-reflection waveform and amplitude illustrate complex patterns of fault-zone fluid content and fluid migration paths. The amplitude map suggests kilometre-wide channels of locally high porosity and thus focused fluid flow. These paths are only subparallel to the expected minimum head, as inferred from the shape of the overlying sediment wedge; other factors must modify fluid concentrations and ultimately migration. Several areas of positive-polarity fault reflections define square-kilometre-sized regions inferred to be lower porosity sections producing strong asperities in an otherwise weak fault. One, coincident with Site 671B, may explain the success of drilling through the fault here. All other holes drilled in the area were within the negative-polarity regions and were unsuccessful in penetrating through the entire fault zone, possibly because of instability associated with high fluid pressures and a weak fault. ODP Leg 156 planned for 1994 will test inferences related to fault permeability and fluid pressures. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.