Source Complexity of the 2015 Mw 7.9 Bonin Earthquake

Abstract

The 30 May 2015 Mw 7.9 Bonin earthquake, one of the largest and deepest earthquakes ever recorded by modern seismology, provides a unique opportunity to study the source process and physical mechanisms of deep-focus earthquakes. We develop a novel back projection technique that allows source imaging in full three-dimensional space with a high-depth resolution. Our results indicate an initial SW-NE bilateral source propagation followed by a northwest source extension. The multiple-source inversion reveals a two-step source process with propagating directions nearly perpendicular to each other, consistent with the 3-D back projection result. The spatial distribution and focal mechanisms of the subevents cannot be modeled by a single planar rupture, which may display a curved rupture plane or subevents crossing multiple fault interfaces. The complex source process can be best explained by stress or structure heterogeneity within the deep slab.