Vertical crustal movements in eastern Taiwan and their tectonic implications

Abstract

Leveling surveys along several routes and tidal observations at various points in eastern Taiwan demonstrate rapid vertical crustal movements, and they provide an effective means for monitoring the effects of collision between the Philippine Sea Plate and the Eurasian Plate. Rapid elevation changes were detected in the southern section of the Longitudinal Valley. Repeated releveling along three routes since 1984 reveals that the Coastal Range was uplifted with respect to the Longitudinal Valley floor at a rate of about 3.0 cm/yr; this deformation is found to be confined within a very narrow zone. Along the east coast of Taiwan, two surveys (1984 and 1987) revealed that the coast is also undergoing uplift, but at different rates (from 0 cm/yr to 3.5 cm/yr). The point of the most rapid uplift is located near 23°N and the rate generally diminishes towards the north; the changes in rates may be controlled by the movements across faults. Tidal observations, while providing a local datum, show that uplift of the tidal station has occurred. Significant horizontal creep has been observed across many faults, but rapid vertical creep, as observed in the Longitudinal Valley, is not very common.