Analysis of Crustal Deformation in Central Taiwan Using Block Modeling with GPS Observations

Abstract:

Taiwan locates in a high seismic activity belt of the southeastern Asia. In central Taiwan, many large earthquakes occurred in historic time, such as the 1906 Meishan (M_L= 7.1), the 1935 Hsinchu-Taichung (M_L=7.1), and the 1999 Chi-Chi (M_w= 7.6) earthquakes. GPS horizontal velocities, in addition, also show a shortening rate of up to 40 mm/yr across the Western Foothill to the Deformation Front. In this study, we employed a method of block modeling to study the interseismic behavior and evaluate slip deficits and earthquake potential of a series of N-S trended active faults in this area. We use the 2002-2012 GPS observations from 155 continuous and 449 campaign stations and set our model with 16 blocks and 12 boundary faults for the central Taiwan (Fig. 1). We first analyzed the sensitivity of the model parameters to the surface deformation for different block configurations, and results indicate that the shallow (<7 km) slips of the boundary faults can be better resolved than the deep (15 km) slips possibly due to the narrow aperture of our geodetic network (Fig. 1). We then calculated the geodetic long-term slip rates, which reflect relative motion between blocks, and the back-slip rates, which reflect interseismic fault coupling, of the boundary faults. Our preliminary results revealed that large rates of slip deficit (>6 mm/yr) occur on the N-S trended Tamaopu-Shuangtung and Sanyi-Chelungpu-Tachienshan-Chukou faults of the Western Foothill rather than the Changhua fault of the Deformation Front (see fault locations in Fig. 1). Although the Chelungpu fault was recently ruptured during the 1999 Chi-Chi earthquake, we may still consider faults to its north, south, and east to have relatively high earthquake potential due to the fast absorption of contracted strain energy across the Western Foothill of Taiwan. Furthermore, two-dimensional dislocation modeling of interseismic fault loading is also under progress to justify the above block modeling results.