Velocity-Interface Structure of the Southwestern Ryukyu Subduction Zone from EW9509-1 OBS/MCS Data |
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Authors: | Wang Tan K McIntosh Kirk Nakamura Yosio Liu Char-Shine Chen How-Wei |
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Institution: | (1) Institute of Applied Geophysics, National Taiwan Ocean University, Keelung, Taiwan, ROC;(2) Institute for Geophysics, University of Texas, Austin, Texas, USA;(3) Institute of Oceanography, National Taiwan University, Taipei, Taiwan, ROC;(4) National Chung Cheng University, Chiayi, Taiwan, ROC |
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Abstract: | A wide-angle seismic survey, combining ocean-bottom seismometers (OBS) and multi-channel seismic (MCS) profiling, was implemented
in the southwestern Ryukyu subduction zone during August and September 1995. In this paper, we present the data analysis of
eight OBSs and the corresponding MCS line along profile EW9509-1 from this experiment. Seismic data modeling includes identification
of refracted and reflected arrivals, initial model building from velocity analysis of the MCS data, and simultaneous and layer-stripping
inversions of the OBS and MCS arrivals. The velocity-interface structure constructed along profile EW9509-1 shows that the
northward subduction of the Philippine Sea Plate has resulted in a northward thickening of the sediments of the Ryukyu Trench
and the Yaeyama accretionary wedge north of the trench. The boundary between the subducting oceanic crust and the overriding
continental crust (represented by a velocity contour of 6.75 km/s) and a sudden increase of the subducting angle (from 5 degrees
to 25 degrees) are well imaged below the Nanao Basin. Furthermore, velocity undulation and interface variation are found within
the upper crust of the Ryukyu Arc. Therefore, the strongest compression due to subduction and a break-off of the slab may
have occurred and induced the high seismicity in the forearc region.
This revised version was published online in November 2006 with corrections to the Cover Date. |
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Keywords: | OBS crustal structure subduction ray travel-time inversion |
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