HR: 10:20h
AN: T42A-01    [Abstracts]
TI: Deformation of Taiwan from Continuous GPS Monitoring
AU: * Wu, F T
EM: wu@binghamton.edu
AF: Department of Geological Sci. State University of New York at Binghamton, Vestal Parkway East, Binghamton, NY 13902, United States
AU: Kuo, L
EM: kuo@earth.sinica.tw
AF: Institute of Earth Sciences Academia Sinica, Nankang, Taipei, 115,
AU: Kuo-Chen, H
EM: kuochen.hao@gmail.com
AF: Institute of Earth Sciences Academia Sinica, Nankang, Taipei, 115,
AB: As of 2006 there are more than 290 continuously recording GPS stations(1,2) now in and around Taiwan and its surrounding islands. We have determined horizontal and vertical velocity vectors, the areal strain rate, the shear strain rate and the volume strain rate. Because of the rapid convergence of Eurasian plate with the Philippine Sea plate (PSP) near Taiwan the trend in the GPS displacement time series is large enough to derive the above- mentioned quantities on a yearly basis and thus track their changes as a function of time. In the following discussions we shall use the Penghu island station (S01R) as reference when relevant. The overall patterns of the velocity vectors in Taiwan reflect the geometry of the plate convergence that created Taiwan. In the mature collision zone of central Taiwan, situated on the Eurasian plate, the velocities are largest on the eastern side and decreases toward the west to very small values in the Coastal Plain. In the south the western side of the Hengchun Peninsula is still moving westward or southwestward at about 50 mm/yr, apparently as a part of the PSP. In general, in central and northern Taiwan, the velocity vectors are oriented WNW but north of about 24ON the velocities become very slow because the PSP has subducted toward the north near that latitude so the collision takes place at depth and the deformation on the surface becomes small. The areal strain rate patterns derived from the horizontal velocities show that although much of Taiwan is under compression, two areas consistently show dilatation: one along the high Central Range and the other one in the northeast coastal area south of Ilan. In the Central Range the dilatation is probably related to the building of the mountain range and in the northeast the subduction of the PSP leaves the top portion a "free boundary". Although the noise level of the vertical time series is about 3 times higher than the corresponding horizontal measurements the continuous data show patterns of deformation. In the few years after the 1999 Chi-Chi earthquake subsidence occurred in many areas but by 2007 many areas had resumed rising. Rates higher than 10 mm/yr are found in a few areas. Several coastal areas show rapid subsidence as a result of water well pumping. Over the period of more than six years, time-dependent variations can be detected. For example, from 2002 through 2006 there appear to be a detectable increase in areal strain. We can expect to see significant changes in deformation of the Taiwan orogen through continuous GPS monitoring. (1) Operated by Central Weather Bureau, Central Geological Survey, Land Survey Bureau, Ministry of Interior, Institute of Earth Sciences, National Taiwan University, and others. (2)For details of the network please see GPSLAB web page of Institute of Earth Sciences, Academia Sinica: http://gps.earth.sinica.edu.tw
UR: http://gps.earth.sinica.edu.tw
DE: 1209 Tectonic deformation (6924)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 8158 Plate motions: present and recent (3040)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting