Slip History of Global Major Deep-focus earthquakes

The physical mechanisms of deep-focus earthquakes puzzle scientists, since the large confining stress would make the deformation ductile than brittle failure. Several hypotheses have been proposed to explain the deep earthquakes, including dehydration embrittlement, transformational faulting and shear thermal instability. In this presentation, we apply a finite fault inversion algorithm to systematically study the slip histories of global deep-focus earthquakes with Mw > 7.0 and depth > 410 km. The finite fault inversion algorithm is based on waveform inversions of body waves in the wavelet domain, and inverts the fault slip, rake angle, rupture initiation time, and slip rate function using a simulated annealing approach. A total of 27 events are investigated, and 19 of them can be reasonably fit by the finite fault inversion. 15 of the 19 events prefer the low-angle fault planes, 2 prefer the high-angle planes, and 2 show ambiguity. A significant number of events have multiple rupture planes, which are spatially and temporally separated and have different slip directions. The poor fitting of the rest 8 events by the finite-fault inversion is perhaps due to existence of focal mechanisms different from those prescribed by the finite fault inversion program. We will discuss how different proposed mechanisms of deep earthquakes explain the seismic results.