Velocitites 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, based on the travel-time observations at Kinman, are determined form Pn arrivals of regional earthquakes. Based on the accurate locations and origin times of shallow earthquakes beneath Taiwan and its eastern offshore region, the uppermost mantle velocities of the Taiwan Strait are determined using seismic waves recorded by stations in the Strait. This 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 improves the epicentral determination of earthquakes on the Strait. The Moho depth beneath the western side of the Taiwan Strait is estimated to be shallower than those beneath both the eastern side Strait is estimated to be shallower than those beneath both the eastern side of the Strait and Taiwan Island. From this data set, the Pn velocities beneath the Strait regions are slightly greater than those of the island area, and the 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 having been slightly deformed due to the arc-continental collision in the Taiwan region.

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