Tomographic signatures and origin of the 2016 Meinung earthquake (Mw 6.7), Kaohsiung, SW Taiwan

Abstract

Abstract In order to investigate the plausible generation mechanism of the 2016 Mw 6.7 Meinung earthquake, a large number of high-quality travel times of P- and S-wave source-receiver pairs are inverted to assimilate high resolution three-dimensional (3-D) seismic velocity (Vp, Vs) and Poisson’s ratio (σ) structures in this study. Our seismic imaging revealed that the 2016 Meinung earthquake occurred along a distinctive edge portion exhibiting high-to-low variations in these parameters in both horizontal and vertical directions across the hypocenter. A continuous low-velocity zone with high-σ is found to be intriguingly associated with the Laonung and Chisan faults where the western upper crust beneath the central coastal plain, western foothills, and southeastern lower crust under the central range are clearly imaged. We propose that weakening of the southeastern crust is attributed to the intrusion of fluids either from the young fold cum thrust fault belt in the shallow crust, or from the dehydration of the subducted Eurasian continental (EC) plate in the lower crust to the upper mantle. The earthquake genesis beneath SW Taiwan is associated with two predominant processes: (i) fluid intrusion into the upper Oligocene to the Pleistocene shallow marine and clastic, shelf units of the Eurasian continental crust; (ii) fluid intrusion into the relatively thin uppermost part of the transitional Pleistocene-Holocene foreland formed along the deformational front due to the subduction of the EC plate. Our estimated models demonstrate that the reduction of anomalous signatures of crustal attributes (Vp, Vs, σ) due to intrusion of fluids might have lowered the seismogenic strength of the source zone and contributed to the genesis of the 2016 Meinung mainshock.