VELOCITIES OF PN-WAVES IN THE TAIWAN STRAIT AND ITS SURROUNDING AREA FROM REGIONAL EARTHQUAKES

P-wave velocities of the uppermost mantle beneath the Taiwan Strait, b ased on the travel-time observations at Kinman, are determined from Pn arrivals of regional earthquakes. Based on the accurate locations and origin times of shallow earthquakes beneath Taiwan and its eastern of fshore region, the uppermost mantle velocities of the Taiwan Strait ar e determined using seismic waves recorded by stations in the Strait, T his study indicates that the average Pn velocities beneath the Taiwan Strait, the island of Taiwan and its eastern offshore region are 8.2 /- 0.2 km/sec, 7.9 +/- 0.1 km/sec and 8.0 +/- 0.1 km/sec, respectively . The uppermost mantle velocity determined for the Taiwan Strait impro ves the epicentral determination of earthquakes on the Strait, The Moh o depth beneath the western side of the Taiwan Strait is estimated to be shallower than those beneath both the eastern side of the Strait an d Taiwan Island. From this data set, the Pn velocities beneath the Str ait regions are slightly greater than those of the island area, and th e Moho dips slightly from west to east. The crust of the Taiwan Strait area could be considered as a part of the Eurasian continent and as h aving been slightly deformed due to the are-continental collision in t he Taiwan region.