How to quake a subducting dry slab at intermediate depths: Inferences from numerical modelling

The origin of intermediate-depth subduction seismicity is a topic of research since long time. While plate unbending is considered as one of the main stress loading mechanisms, the processes responsible for earthquake nucleation are still unclear and depend on the question of whether failure occurs in the wet dehydrating portion of the slab or in the predominantly dry portion. Recently, the seismogenic portions of subducting oceanic slabs have been proposed to consist of dominantly dry metaperidotite that deforms by seismic brittle failure in absence of fluid-mediated embrittlement. In this work, we quantify by numerical modelling the differential stress achievable during unbending of a subducting slab. We show that the presence of discrete hydrated domains in a dry, strong slab amplifies the differential stress to high seismogenic values (ca. 3-4 GPa in the 100-200 km depth range) at intermediate depths. We also consider the effects of low temperature plasticity in olivine that can hinder the build-up of high differential stress to the first 100 km of depth.