A seismic refraction study of the crustal structure in the active seismic zone east of Taiwan

An array of 10 Hawaii Institute of Geophysics (HIG) ocean bottom seismometers (OBSs) was emplaced off the east coast of Taiwan for a cooperative study conducted by scientists from HIG and institutions in Taiwan. As part of this experiment, three overlapping seismic refraction profiles were shot across the array parallel to the coast of Taiwan. The results of the ray trace modeling of these data indicate that the crust off southern and central Taiwan is about 8 km thick in this area and can be modeled by several layers with velocities and thicknesses that lie within the range associated with “normal” oceanic crust. Near 23.5°N a downwarping and thickening of the crustal layers occurs in the model. This downwarped trough of low‐velocity materials may represent the sediment‐filled axis of the Ryukyu Trench. If this is true, it indicates a more southerly trench position in this area than that previously published by other investigators. To the north of this downwarping, the bottom shoals rapidly, and the velocity structure undergoes a transition that may indicate a change to arc or continental type crust.