EPSS Colloquium fall-2018

An improved understanding of the earthquake physics relies on better knowledge of earthquake rupture processes (earthquake nucleation, its complex rupture propagation, and the final arrest) and how faults release stresses through seismic/aseismic slip. Currently, the greatest challenge in this field is that the observations are behind the modeling efforts, making testing and validations of the ever-increasing rupture models impossible. In this talk, I will give an overview of the research activities of my team. We have improved the resolution and reduced the uncertainty of earthquake and tsunami source imaging which allows us to address the open questions of earthquake source dynamics. In the case study of the 2015 Mw 8.3 Chile earthquake, we observed splitting of rupture fronts around the rim of a large barrier. This encircling pattern is analogous to the double-pincer movement in military tactics. Such degree of complexity is previously only seen in simulations and it is observed for the first time in real earthquakes. In the 2011 Mw 9.0 Tohoku earthquake, we find that the coseismic rupture is bounded by the bottom of the seismogenic zone, which contradicts the claims that dynamic frictional weakening enables deep penetrations of large earthquakes into the ductile creeping zone. My team is also enhancing and combining the next-generation detection techniques (e.g. template matching, machine learning, array processing) to monitor microseismicity and tremors. In several case studies, we detect wide distributions of undocumented foreshocks and repeating earthquakes ahead of large earthquakes, suggesting early nucleations driven by large-scale aseismic slow slip. We also identify two episodes of deep clusters of seismicity below the Kilauea volcano crater ahead of its April 2018 eruption. The episodic activation of deep seismicity is indicative of movement of pressurized magma, an early precursor of the volcanic eruption. These studies demonstrate the capability of the enhanced detections to illuminate the underlying physical mechanisms behind various micro-seismic processes.