Speaker: Dr. Zhongwen Zhan, Assistant Professor of Geophysics at the California Institute of Technology
It has been about 90 years since the discovery of deep earthquakes, and their mechanisms remain unclear. On one hand, they appear to be similar to shallow earthquakes as shear dislocations with diverse rupture properties. On the other hand, they have intriguing differences from shallow earthquakes, such as the spatially variable b values and low aftershock productivity. In this talk, I will review seismic observations of deep earthquakes and present a dual-mechanism hypothesis: deep earthquakes initiate with transformational faulting, which are brittle and spontaneous, and may propagate with the same mechanism, or trigger a non-spontaneous and dissipative mechanism such as shear melting to continue the rupture. In the end, I will discuss several specific, testable predictions of this hypothesis and our current efforts in testing some of the predictions.