Ongoing Research

In order to address the key questions, we have developed a multidisciplinary approach.  The major active faults have long been identified and the structure of the foothills is well documented from geological and geophysical investigations. However, the long term slip rates on the major active faults remain poorly known. This is a major missing piece of information. We have therefore  started field investigations to estimate the slip rates on the Changhua, Chelungpu and Tiechenshan faults which are the major frontal faults in the Western Foothills within the Chichi area, as well as on the maon fault in eastern Taiwan along the Longitudinal Valley and Coastal range.  In parallel we are investigating the thermal structure and exhumation history of the range by combining (U-Th)/He thermochronology and RSCM thermometry.  In this collisional context, rocks are accreted to the range and ultimately exhumed, offering an opportunity to determine the temperature field from thermo-barometric studies associated with  thermokinematic modeling.

We should thus be able to determine not only the kinematics of crustal deformation across the range and the Western Foothills over a time scale of a few ka to a few Ma, but also the thermal history and present thermal structure of the range. This study should shed light on orogenic processes and on the influence of temperature on crustal deformation.

We are currently analyzing geodetic data on postseismic deformation due to the Chichi earthquake which seem to have resulted from a combination of frictional afterslip and viscous relaxation.  By comparing interseismic, co and post-seismic deformation with the structure and thermal model of the range we hope to understand better the key parameters controlling the mechanical behavior of the crust and major thrust faults as the Chelungpu fault.

Overview of scientific results

Neotectonics

• Bruce Hsu, Kerry Sieh, Yue-Gau Chen and their Taiwanese collaborators have produced a neotectonic map of Taiwan. A manuscript is in review at JGR (B. Hsu et al)
• Determination of slip rate on Pakuashan and Chelungpu fault. This study has lead to a major methodological development regarding the determination of geological shortening rate across a fault-propagation fault. These results were presented at AGU 2004 Fall meeting and two manuscripts are in review at JGR (Simoes et al).
• Eastern Taiwan. The pattern of deformation across the Longitudinal Valley is now  better constrained from Morocco and its relation to past seismicity. One manuscript on the 1951 earthquake has been submitted (B. Hsu et al)

Structural and thermal evolution

• The samples for thermometric and thermochronology investigations have been collected and have been analyzed partly. A manuscript is in preparation (Beyssac et al) .

Geodesy

•  Yaru Hsu , Mark Simons, Shui-Beig Yu have produced a model of interseismic deformation (Y.R. Hsu et al, EPSL, 2003).
• A model for postseismic deformation and aftershocks triggering has been proposed (Perfettini and Avouac, JGR, 2004)

Chi-Chi earthquake

• The kinematics of the rupture has been determined from the inversion of teleseismic waveforms, strong motion and geodetic measurements (Ji et al, 2001).
• Coseismic deformation was measured from SPOT images (Dominguez et al, 2003), and from SAR interferometry (Levy et al, 2005).

A preliminary survey for the deployment of 6 cGPS stations occurred in the Fall of 2004. The stations will be installed in 2005.