P-wave velocity structure of upper crust in the vicinity of the Yangsan Fault region

This study presents the P-wave velocity structure of the upper crust in the vicinity of the Yangsan Fault region based on travel-time inversion of thirty-five digital secmic records obtained by the Korea Institute of Geology, Mining and Materials (KIGAM). The present model consists of 8 horizontal layers with constant velocity in the subsurface depth of 18 km. Two-point ray tracing is applied for travel-time inversion and determination of hypocenteral parameters of the earthquakes to reduce errors resulting from ray path. The computational results of travel-time inversion show that (1) a velocity gradient with depth is nearly constant in the subsurface depth of 8 km, (2) a low-velocity zone exists in the depth between 10 and 15 km, and (3) a relatively large velocity discontinuity appears at about 15 km.