Deformation of the Philippine Sea Plate Under the Coastal Range, Taiwan: Results From an Offshore-Onshore Seismic Experiment

Abstract

The ongoing orogeny in Taiwan is a result of the collision of the Philippine Sea and the Eurasian plates. While the structure of the continental crust on the Eurasian plage (EP) is now mostly known, that of the oceanic crust on the Philippine Sea Plate (PSP) is not well mapped. Using offshore onshore refraction data, collected during the R/V E wing cruise of 1995, we investigate the nature of the transition between the EP and the PSP in the vicinity of the southern Coastal Range of Taiwan. The data were produced by the air-gun array of the R/V Ewing along a WNW-ESE trending line off the coast of central Taiwan (MCS/OBS line 23). The refracted P waves were collected by 19 RefTek recorders with L-28 sensors placed along the southern cross-island highway of Taiwan, which is the onshore extension of line 23. Beacause of high noise levels in the Coastal Plain, we were only able to retrieve usable data from 11 stations located from the east coast through the Central Range. We performed forward modeling of the first arriving waves at these stations; our strategy was to search for the simplest model that fitted all the data. Our results indicate that the crust thickens gradually toward Taiwan, from about 9-12 km thick in the Huatung basin to 15-18 km thick off the eastern coast of Taiwan, with a 4-8 degree dip of the Moho. Continuing westward, the crust thickness more rapidly to 27-32 km thick under the east coast of Taiwan, with a 26-32 degree dip of the Moho.

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