Near Real-time Waveform Inversion for Finite-source Rupture in 3D Structure

Monday, 15 December 2014
Ming-Che Hsieh, Institute of Geophysics National Central University, Jhongli, Taiwan, Li Zhao, Academia Sinica, Taipei, Taiwan, Chen Ji, University of California Santa Barbara, Santa Barbara, CA, United States and Kuo-Fong Ma, NCU National Central University of Taiwan, Jhongli, Taiwan
Advances in observational and computational technologies in the past two decades have made it possible for automatic, real-time solutions of the focal mechanisms of earthquake point sources. However, seismic wave radiations from moderate and large earthquakes often exhibit complex directivity behavior that can only be explained by rupture processes that are finite in both space and time. We develop an efficient and effective approach to determining the finite-rupture models of moderate and large earthquakes by fitting synthetic and recorded broadband waveforms. A Green tensor database is established which enables rapid calculations of accurate synthetic seismograms in three-dimensional structural models with realistic surface topography without the need for high-performance computing. A three-step process is used in solving for a finite-source model: A point-source focal mechanism is determined in the first step. Then, the two nodal planes in the point-source solution are used as trial candidates to solve for an average finite-rupture model and identify the actual fault plane. In the final step, a finite-fault slip distribution inversion is carried out based on the identified fault plane. Applications to moderate events (MW≈6) in Taiwan show that our source inversion technique is effective for semi-automatic, near real-time determinations of finite-source parameters for seismic hazard mitigation purposes.