Across-Slab Propagation and Low Stress Drops of Deep Earthquakes in the Kuril Subduction Zone

Deep earthquakes occur down to 700 km depth where pressure is up to two orders of magnitude greater than in the crust. Rupture characteristics and propagation mechanisms under those extreme conditions are still poorly constrained. We invert seismic waveforms for the spatial dimensions, duration and stress drop of deep-focus earthquakes (M-w 6.7-7.7) in the Kuril subduction zone. We find stress drops of similar to 1-10 MPa and rigidity-corrected spatial dimensions and durations similar to crustal earthquakes. Radiated efficiency >1 is observed, suggesting that undershooting is prevalent in deep earthquakes, consistent with laboratory derived weakening mechanisms. Comparisons with subduction models suggest across-slab propagation within regions with temperatures T < similar to 1,000 degrees C, similar to shallow events. Hence, despite different triggering mechanisms, the same physics seems to control the rupture propagation of both shallow and deep earthquakes.

Automated summary

This study investigates the rupture characteristics and propagation mechanisms of deep earthquakes using seismic waveforms. The results show that deep earthquakes have similar stress drops, spatial dimensions, and durations as crustal earthquakes, and exhibit high radiated efficiency. Comparisons with subduction models suggest that deep earthquakes and shallow earthquakes are controlled by the same physics in terms of rupture propagation.