Crustal Structure at the Intersection of the Ryukyu Trench with the Arc-Continent Collision in 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 Plate (EP) is now mostly known, that of the oceanic crust on the Philippine Sea Plate (PSP) has never been well mapped. Using offshore-onshore refraction data, collected during the R/V Maurice Ewing cruise of 1995, the nature of the transition between the EP and the PSP at the Ryukyu Trench and the Longitudinal Valley, Taiwan was investigated. The data were produced by the air-gun array of the R/V Ewing along two roughly east-west trending lines off the coast of northern Taiwan (R/V Ewing Lines 14 and 16). The refracted P waves were collected by 19 RefTek recorders with L-28 sensors placed along the Central Cross-Island Highway of Taiwan, which is the onshore extension of Ewing Line 16. Because of high noise levels in the Coastal Plain and equipment failure at stations near the east coast, only data retrieved from nine stations in the Central Range were considered usable. To obtain crustal structure, an inversion and forward modeling scheme was followed and the results indicate that the Moho discontinuity gradually increases depth from about 30 km below sea level under the Nanao Basin to about 37 km below sea level under the Eastern Central Range. Additionally, the model of the northern profile contains a relatively low velocity zone off the east coast, possibly as deep as the lower-to-middle crust.

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