Understanding Earthquake Physics Through High Frequency Multiple Point Source Inversion and Earthquake Cycle Simulation

Dr. Shi Qibin

University of Washington

2022.03.11（星期五）15:00，腾讯会议号：325-884-389

报告摘要：

Deep insights to earthquake physics is crucial for seismic hazard assessment and mitigation. To understand the fundamental earthquake source parameters and fault slip process and their relationship and interaction with geological structure, we focus on using kinematic earthquake rupture inversions and physics-based earthquake cycle simulations. To better resolve earthquake kinematic source processes, we develop a novel multiple-point-source focal mechanism inversion method based on a Markov chain Monte Carlo (MCMC) nonlinear inversion scheme. This method is characterized by cutting and pasting waveform segments and calibrating the paths, which allow inversion to be conducted at as high frequency as we can (e.g. approaching 1Hz). We validate this inversion method by applying it to the 2016 Mw6.2 Kumamoto foreshock in Japan. Our high frequency inversion resolves the anti-dipping fault geometry that is highly consistent with high-resolution seismicity and full moment-tensor solution. We then apply it to the Mw7.1 Kumamoto mainshock and reveal a unilateral rupture towards the Aso volcano. The rupture process is shallowing towards higher thermal gradient (Aso), eventually stopped by fault branching. The application of our method to resolving the rupture of the 2020 Mw7.8 Alaska megathrust earthquake using nearfield high-rate GPS data requires modification of source time function to allow Yoffe-shape (an asymmetric shape source time function). This new source time function inversion scheme reveals that the up-dip rupture has a long tail Yoffe source time function and down-dip rupture has a symmetric and impulsive cosine shape source time function. We interpret the inversion result as a mix of crack-like rupture (up-dip) and pulse-like rupture (down-dip), possibly as the first confirmed case. We also find that the geometric irregularities of the plate interface delayed the coseismic rupture and produced 20 degree slip direction difference between sub-events. Finally, we conduct earthquake cycle simulations to mimic highly diverse slip behaviours on the Nankai subduction zone plate interface, which include full and partial earthquake ruptures, long- and short-term slow slip, slow earthquakes and creep, in addition to the viscoelastic flow of the upper mantle. We successfully reproduce the typical down-dip segmentation of slip behaviours that are controlled by the geological structure of the overriding plate and the complex interactions of the various slip behaviours during seismic cycles.

报告人简介：

Shi Qibin received his PhD at the Earth Observatory of Singapore(EOS), Nanyang Technological University. Before he joined EOS, he obtained his Bachelor degree in geophysics from Nanjing University. He is particularly interested in earthquake source process, earthquake physics and machine learning. His PhD research has focused on deriving kinematic earthquake rupture processes from the observations and simulating the earthquake cycles for better understanding of earthquake physics.