S-wave velocities and anisotropy in sediments entering the Nankai subduction zone, offshore Japan

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doi: 10.1111/j.1365-246X.2009.04430.x
Author(s): Peacock, S.; Westbrook, G. K.; Bais, G.
Author Affiliation(s): Primary:
University of Birmingham, School of Geography, Earth and Environmental Sciences, Birmingham, United Kingdom
Volume Title: Geophysical Journal International
Source: Geophysical Journal International, 180(2), p.743-758. Publisher: Wiley-Blackwell on behalf of The Royal Astronomical Society, the Deutsche Geophysikalische Gesellschaft and the European Geophysical Society, International. ISSN: 0956-540X
Note: In English. 65 refs.; illus., incl. sects., 4 tables, sketch maps
Summary: P and mode-converted S waves from airgun shots recorded along a line of ocean bottom seismometers were used to construct a 2-D velocity section across the Nankai Trough and the toe of the accretionary complex, offshore southeast Japan. The site was chosen because of plans to drill into the seismogenic zone of the main subduction thrust, which has a history of M∼8 earthquakes. The section is constrained by well-log data from three Ocean Drilling Program boreholes. S-wave velocities of the sediments over the entire section, down to >1.1 km below seafloor, range from 107 to 915 m s-1. Shear wave splitting indicates anisotropy in all the sediments except possibly the distal trench fill. If interpreted conventionally as being due to vertical stress-aligned cracks, the anisotropy in both the trench and the toe of the accretionary wedge is consistent with crack orientation NW-SE, parallel to the direction of maximum tectonic compression. Crack density is ∼0.01-0.03, consistent with closeness to fracture criticality. Abstract Copyright (2010), RAS.
Year of Publication: 2010
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Accretion; Anisotropy; Asia; Bathymetry; Body waves; Density; Elastic waves; Far East; Integrated Ocean Drilling Program; Japan; Leg 190; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; ODP Site 1174; Ocean Drilling Program; Pacific Ocean; Plate tectonics; Prestack migration; Processes; S-waves; Seismic migration; Seismic waves; Subduction zones; Traveltime; West Pacific
Coordinates: N320000 N330000 E1350000 E1340000
Record ID: 2010030758
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom