Dynamic Ruptures of The 2016 Ml 6.6 Meinong Earthquake and Potential Ground Motion from Scenario Earthquakes on the Chinshan-Shanqiao Fault, Taiwan, with 3D Velocity Structures

Abstract

Dynamic ruptures of the 2016 Meinong earthquake and potential ground motion induced by earthquake scenarios on the geometrically complex Chinshan-Shanqiao faults in Taiwan have been modeled. Realistic 3D velocity structures have been incorporated for Chinshan-Shanqiao earthquake scenarios. In the first study, we use dynamic ruptures to reproduce slip distribution, rupture process and moment rate history from Meinong earthquake kinematic inversions to understand the mechanics that causes the complex rupture details. The earthquake occurs on a buried and shallow dipping fault with dominant left-lateral strike slip with limited amount of thrusting. By trial-and-error, we find in our best fit model two asperities with sizes of 15 by 8 km and of 10 by 6 km that dominate the moment release. The average stress drops in the two asperities are 5.0 and 3.5 MPa, respectively. The whole rupture region is 25 by 25 km. Except for asperities, the region near the hypocenter has a very low 0.75 MPa stress drop. The magnitude of the best model is Mw 6.63 and the maximum slip is 1.4 m, close to Mw 6.52 and 1.2 m from inversions. We apply a uniform velocity structure to simulate ground motions and find the simulated peak ground velocities match the seismograms on rock sites in 0-0.5 Hz. Inside low-velocity sedimentary Tainan basin, simulated peak ground velocities also match the recorded vertical peak ground velocities. However, the horizontal peak ground velocities are less than those from records. Therefore, we conclude that the uniform velocity structure works well for the rock sites but 3D velocity structure is important to generate the large horizontal ground motions recorded in the Tainan basin during the earthquake. In the second study, we simulate potential ground motion from scenario earthquakes on the geometrically complex Chinshan-Shanchiao faults. Realistic 3D velocity structure including the low-velocity sedimentary basin is included. The Chinshan-Shanchiao fault is the west bound to the Taipei basin in northern Taiwan. It is a highly active normal fault with left strike-slip components and is speculated to host a potential future earthquake with a magnitude over 7.0. By comparing models with uniform and 3D realistic velocity structure, we find that seismic energy can be trapped in the Taipei basin. Stations inside and on the edge of the basin show amplified peak ground acceleration and prolongated waveforms. The kink fault geometry also contributes to amplification of ground motion. The peak ground acceleration and peak ground velocity of the stations in the west of the basin are larger than those in the east of the basin. This effect appears to be related to the shape of the basin.