Search

The physical mechanisms governing earthquakes clarify the dynamic processes at Earth’s plate boundaries and inform the evaluation of global seismic hazards. One effective method of interrogating these mechanisms involves imaging earthquake source processes with the back-projection method, which time-reverses seismograms recorded at arrays of seismometers to determine the spatiotemporal evolution of the sources of seismic waves. This method benefits from dense and large aperture arrays and has therefore gained considerable utility with the advent of seismic networks such as the Hi-net array in Japan and the USArray in North America. As instrumentation has improved, so have the techniques enhancing the resolution of back- projection images. Such developments in instrumentation and methodology have discerned increasingly finer scale details of the largest earthquake ruptures and lowered the magnitude threshold required to determine the finite source processes of smaller earthquakes. This dissertation outlines improvements to the back-projection method that image the rupture properties of earthquakes across diverse depth ranges and tectonic environments. First, a novel genetic algorithm-based back-projection technique using data recorded at teleseismic distance windows (30°–90°) images the complex source process of the 2018 Mw 6.9 Hawaiʻi earthquake, revealing the heterogenous frictional properties of the décollement hosting this event and informing hazard estimates of future large magnitude events near Kīlauea (Appendix A). Second, the acceleration of the 2017 Mw 7.7 Komandorsky Islands earthquake to supershear speeds across a fault stepover is observed for the first time in nature using a similar back-projection method and regional (0°–35°) seismic data (Appendix B). This type of supershear transition, having only been previously documented by numerical modeling efforts, has significant implications on the evaluation of the elevated seismic hazards associated with sup