Two-stage rupture during the Mw 8.3 Okhotsk 2013 deep-focus earthquake constrains slab geometry

The Mw 8.3 deep-focus earthquake beneath the Okhotsk Sea in 2013 provides an opportunity to study the source mechanism with regard to the specific geometry of the slab in the hypocentral region. It is also an opportunity to observe the impact of such a major event on the mechanical functioning of the subduction. Here we investigated the intricate rupture processes of the earthquake through back-projection using global stations. The earthquake can be divided into two stages, each consisting of multiple sub-events. Our teleseismic back-projection results suggest that the first stage of rupture occurred on multiple sub-horizontal planes and propagated to greater depths during the second stage. The main part of the rupture is consistent with transformational faulting within the metastable olivine wedge. The complex rupture process during the great earthquake can be put into perspective with the variations in the rate of plunge observed before and after the earthquake. While the earthquake was facilitated by a transient plunge a month before, it allowed a form of asperity to disappear through thermal runaway on a dipping plane and consequently led to an acceleration in the rate of subduction over the last 10 years. Teleseismic back-projections of the Mw 8.3 2013 Okhotsk earthquake suggest initial transformational faulting on sub-horizontal planes within the metastable olivine wedge was followed by deeper propagation of ruptures driven by thermal runaway.