Re-Examining Temporal Variations in Intermediate-Depth Seismicity

Changes in the frequency of intermediate-depth (60–300 km) earthquakes in response to static stress transfer can provide insights into the mechanisms of earthquake generation within subducting slabs. In this study, we use the most up-to-date global and regional earthquake catalogs to show that both the aftershock productivity of large earthquakes, and the changes in the frequency of intermediate-depth earthquakes around the timing of major megathrust slip, support the view that faults within the slab are relatively insensitive to static stress transfer on the order of earthquake stress drops. We interpret these results to suggest the population of faults within the slab are much further from their failure stress than is typical for shallow fault systems. We also find that aftershock productivity varies within slabs over small spatial scales, indicating that the mechanism that enables faults to rupture at intermediate depths is likely to be spatially heterogeneous over length-scales of a few tens of kilometres. We suggest dehydration-related weakening mechanisms can best account for this heterogeneity.