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Using core properties and seismic reflectivity to estimate pore pressure in an active decollement fault
Authors:
Tobin, H.J. (Stanford Univ., CA (United States))
Moore, J.C. (Univ. of California, Santa Cruz, CA (United States))
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| Abstract: In the decollement zone of the Barbados accretionary prism, a 3-D seismic image exhibits patchy high-amplitude negative polarity reflections, which have been attributed to large overpressures confined to the fault zone.^We collected laboratory P-wave velocity and porosity vs. pore pressure data, using core samples from and adjacent to the decollement zone at ODP Site 948.^Logs constrain density and velocity through the decollement zone at Site 948.^We use these data to calibrate the reflectivity of the fault zone to pore pressure through waveform and amplitude models of the fault plane reflections.^Modeling of the positive polarity Site 948 reflection indicates that it can be explained by a lithologic boundary coincident with the decollement, without anomalous fault properties.^By contrast, the dominantly-negative polarity waveform of the reflection [approx]2 km arcward (beneath Site 947) is best modeled by inserting a 16-19 m thick zone of extremely low impedance into the Site 948 impedance structure, with a gradational return to [open quotes]normal[close quotes] impedance just above the positive boundary.^Relative amplitudes in this reflection indicate a larger impedance contrast than can be accounted for at sub-lithostatic fluid pressure, based on the core properties data.^We conclude that lithostatic pore pressure with attendant hydraulic dilation of the fault zone is required to generate the negative-polarity reflections.^Mapping of these reflections thus delineates zones of elevated fluid content and zero effective stress in the fault zone. |
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| Publication Date: |
01 Jan 1996
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| Report numbers: |
CONF-960527--
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| Resource Type: |
Conference
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| Resource Specific Type: |
Journal Article
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| Resource Relation: |
AAPG Bulletin; Vol/Issue: 5; Annual convention of the American Association of Petroleum Geologists, Inc. and the Society for Sedimentary Geology: global exploration and geotechnology; 19-22 May 1996; San Diego, CA (United States)
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| Country of Publication: |
United States
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| Language: |
English
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