- Webb Hall 1025
Xiangyu Li will present his PhD defense entitled "Multiple double couple analysis of recent large earthquakes and its application in detecting the dynamic stress triggering events."
Currently, the source mechanisms of global large and moderate earthquakes are routinely constrained and reported by multiple agencies using long-period seismic signals. However, these conventional analyses simplify the rupture process of an earthquake as single point source, which is not appropriate if this earthquake has a fault dimension comparably larger than the signal?s dominant wavelength or includes multiple subevents with different focal mechanisms. Source complexities in terms of irregularity in the rupture propagation and distribution of moment release can yield distinct seismic waves, and therefore might be deciphered through more carefully waveform modeling.
This dissertation first introduces a new nonlinear inverse algorithm which approximate the earthquake as multiple double couple sources (MDC) and constrain them simultaneously using seismic data. This method has been applied to local and global large earthquakes using long-period signals, teleseismic body waves and local broadband strong-motion records. The results demonstrated that more source information could be extracted using this new method, but its spatiotemporal resolution depends on the station coverage and frequency contents of seismic signals. This MDC analysis also allows us to detect and study the large events occurring right after a large earthquake. Because their observations are contaminated by the seismic waves excited by the earlier event, their focal mechanisms then cannot be constrained well using conventional methods. The second portion of this thesis focuses on dynamic interaction between these pair of events. Through carefully studying the 2000 Mw 8.1 New Ireland earthquake doublets and the mud volcano associated 2013 Pakistan Mw 7.8 strike-slip event, we find that these subsequent event are correlated with the dynamic stress perturbation, rather than static stress perturbation, excited by the mainshock.
The implements of high-quality broadband seismograph networks globally and advances in parallel computational capability enable us to conduct MDC analysis automatically for global large earthquake and provide more precise priori information for the subsequent finite fault inversion. It then shall be an important contribution to the routine real-time earthquake hazard analysis.