Short-term, Seasonal, and Long-term Deformation in the Central Range of Taiwan Induced by Earthflows

Abstract:

Seasonal GPS motions are often attributed to hydrological loading and other environmental factors. For the first time we observe GPS seasonal motions associated with slow-moving landslides (earthflows). The directions of GPS movements after heavy rains and in the wet season are consistent with the slope directions derived from a high-resolution elevation model constructed by airborne Light detection and Ranging (LiDAR). Seasonal and long-term interseismic motions are modulated by slow-moving landslides. GPS observations of seasonal motions at Lushan suggest continuous creeping of earthflows at a rate of ~15 mm/yr in the wet season. Six out of 26 cGPS sites in the Central Range of Taiwan affected by earthflows show 25%~40% differences in amplitudes of interseismic velocities compared with the adjacent stable cGPS sites. Estimates of interseismic crustal strain can be biased without taking account surface processes. Preliminary analyses indicate rainfall and topography play stronger roles on the occurrence of earthflows compared to seismic activity and lithology. Discrimination between surface processes and tectonic-origin motions is the key to natural hazard assessments.