Global Positioning System Measurements of Crustal Deformation in the Taiwan Arc-Continent Collision Zone

Abstract

A 78-station 270 km wide Global Positioning System (GPS) network which spans the arc-continent collision zone in southern Taiwan has been surveyed 5 times from 1990 to 1994 with dual-frequency geodetic GPS receivers. The observed data are processed with Bernese software, v.3.4, using the available precise ephemerides. The unknown residual tropospheric zenith delays are estimated once per 6-8 hour session for each station in the least squares adjustment of carrier phase observations. The standard errors of GPS observed lengths are in the range of 5 to 9 mm for a baseline of 3-120 km in length. The changes in baseline length are utilized to study the spatial variations of crustal strain and estimate the relative velocities of geodetic stations. We found that the deformation zone caused by the active collision process is probably 200 km in width. The Coastal Plain, eastern part of the Western Foothills, Central Range, and Coastal Range show slight to moderate strain rates. Remarkable contractions of 0.51-1.65 μstrain/yr in 100°-120° are detected in the vicinity of the Chukou fault. The Longitudinal Valley gives extremely high shortening rates of 3.2-6.1 μstrain/yr in 109°-133°. It is obvious due to the aseismic slip on the Longitudinal Valley fault as previously demonstrated by trilateration data. The velocity field of GPS stations reveals a fan-shaped pattern consistent with the directions of maximum compressional tectonic stress inferred from borehole breakout data, earthquake focal mechanisms, and Quaternary geological data. The GPS observed velocity of Lanhsu on the Luzon arc relative to Paisha, Penghu of the Chinese continental margin, 86.3+2.4 mm/yr in 307°±1°, is almost in the same direction as that proposed by Seno (1977) or Seno et al. (1993), but the rate is about 15-20% faster.