Efficient waveform inversions for finite-source models of moderate and large earthquakes in three-dimensional structures

• Main Authors: Ming-Che Hsieh, 謝銘哲
• Other Authors: Li Zhao
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/06919330181140364420

博士 === 國立中央大學 === 地球科學學系 === 103 === For hazard mitigation and risk assessment, an efficient and well-designed algorithm to determine earthquake rupture properties in a short time is on demand. It is also important to account for effects of surface and subsurface structures to wave propagation and predict ground motion more accurately. In this thesis, we have developed an efficient three-step process which 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 full slip distribution inversion is carried out based on the identified fault plane. We have adopted the source determination scheme to earthquakes near Nantou in central Taiwan for tectonic interpretations. We solved for the rupture properties of a series of moderate events (MW≈6), which show similar focal mechanisms but with different focal depths. Our determination on the rupture planes of these earthquakes suggest that the most of the shallow-focus ruptures occur on the low-angle plane, but on the high-angle plane for most of the deeper events, consistent with the background seismicity and support the existence of tectonically co-located active conjugate faulting system in central Taiwan. We also demonstrated the slip distribution inversion of a moderate earthquake in eastern Taiwan by our three-step procedure. Both broadband and strong motion stations are included in the inversion. Our results show that three-dimensional velocity model could provide better waveform fittings than one-dimensional model, and slip distribution is much more concentrated. Applications to moderate events (MW≈6) in southeastern and eastern 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.