Spontaneous Triggered Aseismic Deformation Transient in the Southernmost Tip of Active Taiwan Mountain Belt Using Geodetic and PSInSAR Techniques, 2002 - 2013

Abstract:

The seismic hazard of the Hengchun fault in the southernmost tip of Taiwan has been concerned for a long time due to the discrepancy between long-term and short-term vertical motion. The long-term uplift is inferred from the dating data of the oceanic terraces across of the Hengchun fault while the short-term subsidence is derived from the geodetic data from 2002 to 2006. In this study, we therefore first adopted the GPS observations and precise leveling measurements during 2002-2013 to comprehend the kinematics of the active fault in Hengchun peninsula and its seismic hazard. Three different deformation patterns are revealed in three stages separating by the 2006 M_L 7.0 Pingtung offshore earthquake and April 2010. Before the 2006 earthquake (stage 1), subsidence rate of ~2.0 mm/yr are shown across the Hengchun fault. After the 2006 event (stage 2), the subsidence rate in the western region is ~3.2 mm/yr, while the eastern region has a 2.5 mm/yr uplift rate. After April 2010 (stage 3), the western region starts to show minor uplift at the rate of 0.1 mm/yr, and the eastern region displays a 2.3 mm/yr uplift rate. With the average vertical velocity of the southern leveling route decreased by 0.6 mm/yr and the northern leveling route increased by 3.2 mm/yr, we observed a northward propagating trend of the vertical component during the December 2006 – April 2013 period. For the horizontal velocity field, azimuths of the velocity change from 275° to 270° in southwestern region after the 2006 event. After April 2010, azimuths change again from 290° to 292° in eastern region. Based on our preliminary tests, the velocity changes in three stages are not significantly contributed by the postseismic deformation associated with the 2006 Pingtung earthquake. On the contrary, the increase Coulomb stress change triggers the aseismic creep on the high angle Hengchun reverse fault. To further analyze the kinematics of this fault, we will include the PSInSAR technique and kinematic model in this study in the future to understand the seismic hazard of the Hengchun fault.