Crustal Structure in Central Japan as Derived from the Inabu Quarry Blast Observations

Abstract

On September 2, 1976, a 7.5 tons quarry blast was made at Inabu, in the northeastern part of Aichi Prefecture. The crustal structures along the two profiles in central Japan were investigated using the seismic waves generated by this quarry blast. In travel time curves, there are gaps of about 0.5sec and 0.3sec. These travel time gaps may be attributable to the Median Tectonic Line and the Yoro Fault, and vertical offsets at these faults were calculated as 6.3km and 5.3km, respectively. A granitic layer, which has been considered to have a velocity of about 6.0km/sec, can actually be divided into two layers with velocities of 6.0km/sec and 6.3km/sec, and beneath these layers a basaltic layer exists with a velocity of 6.8-6.9km/sec. There is no clear phase which shows the Pn velocity.