Two-dimensional P-and S-wave velocity structure of the Yamato Basin, the southeastern Japan Sea, from refraction data collected by an ocean bottom seismographic array.

Abstract

A P- and S-wave velocity structure across the Yamato Basin, southeastern Japan Sea, was modeled on the basis of seismic data acquired during the DELP-85 Wakashio Cruise conducted by the Japanese Research Group of the International Lithosphere Project (ILP). Forward modeling of seismic wave field using the ray theoretical method was carried out to analyze the refraction data of two seismic profiles: one is a profile (230 km long) at the middle of the oblong basin along its strike (line A) and the other is perpendicular to it (line B). The result indicates that the crustal layering is twice as thick as in a normal oceanic basin but the P-wave velocity in each layer is very similar to that of the oceanic basin crust. The upper mantle has a P-wave velocity of 7.9-7.7 km/s in line A, and 8.3 km/s in line B. Moho is flat in line A with 17 km depth and is bowl-shaped in line B rising toward 14 km depth at both sides. The S-wave velocity model has a low velocity zone at depths between 12 and 16 km.