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

Description: 

Deep earthquakes occur when subducting slabs dive into the mantle at depths of up to 700 km, where pressure is up to 100 times greater than in the crust. These high pressures and temperatures should prevent the occurrence of earthquakes, and it is still unclear how deep earthquakes start or propagate under these conditions. In our recently published study, we inverted seismic waveforms using a second-degree moments approach for the spatial dimensions, duration and stress drop of eight deep-focus earthquakes (Mw 6.7—7.7) in the Kuril subduction zone. We find stress drops of 1—10 MPa, and after adjusting for changes in rigidity with depth, we find that the spatial dimensions and durations of the deep earthquakes are similar to crustal earthquakes. We also measured values of the radiated efficiency (the ratio of radiated energy over available strain energy). For these earthquakes, radiated efficiency >1 is observed, suggesting that undershooting is prevalent in deep earthquakes, consistent with laboratory-derived weakening mechanisms. When we compared the earthquake spatial extents to thermal subduction models, we found these deep earthquakes were confined to the coolest part of the slab, with temperatures T<1000 °C, similar to shallow events. Hence, despite different triggering mechanisms, the same physics seems to control the rupture propagation of shallow and deep earthquakes.

Session: Characteristics and Mechanics of Fault Zone Rupture Processes, from Micro to Macro Scales - I

Type: Oral

Date: 5/2/2024

Presentation Time: 08:30 AM (local time)

Presenting Author: Alice

Student Presenter: No

Invited Presentation: 

Authors