Assessing Fault Slip and Seismic Hazard in Taiwan using Space Geodesy

Taiwan is a geologically complex region due to the continuous collision of the Eurasian Plate and the Philippine Sea Plate. This study aims to quantify the crustal deformation of Taiwan and detail the islands seismic hazard potential using space geodesy. Data is collected between 2016 and 2021 through C-band Copernicus Sentinel-1 synthetic aperture radar (SAR) imagery and continuous GNSS data from Academia Sinica, Taiwan. We exclude major earthquake events within this time period and generate Interferometric SAR (InSAR) time series in ascending and descending tracks using open-source code ISCE. We combine the ascending and descending InSAR measurements to produce east-west and vertical velocities, and set the velocities to the same reference frame with GNSS measurements. We then construct a block model based on active fault traces, published block geometries, InSAR velocity gradients, and geologic maps. We use the total variance regularization approach to determine the best fitting number of unique blocks based on the collected InSAR and GNSS datasets, and to estimate block rotation and fault slip budget on the faults bounding the blocks. The InSAR and GNSS results reveal > 8 cm/yr of northwestward shortening from east to west Taiwan and > 4 cm/yr of subsidence in west Taiwan. The high spatial resolution of InSAR identifies several creeping faults throughout southwest and east Taiwan. The preliminary block model suggests (i) divergent fault slip in northeast Taiwan consistent with the back-arc opening of the Okinawa Trough, (ii) a series of fault convergences accommodating distributed crustal deformation in the Western Foothills in west Taiwan and along the major plate boundary fault, the Longitudinal Valley fault, in east Taiwan, and (iii) significant strike-slip motion accompanied by tectonic escape in southwest Taiwan. Continued work on fault slip budget will allow us to estimate potential seismic hazard in Taiwan.