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Shallow Serpentinization Promoted the Up-dip High-Frequency Seismic Wave Radiation During the 2021 Mw8.1 Kermadec Megathrust Earthquake

Description: 

It has been widely observed that large megathrust earthquakes are featured by frequency-dependent rupture with high-frequency (HF) seismic waves primarily radiated from the down-dip portion of the coseismic slip, which has been attributed to the mechanic heterogeneity at the lower boundary of the locking zone. In contrast to this common belief, here we report that during the 2021 Mw 8.1 Kermadec megathrust earthquake, the HF energy was mostly radiated from the up-dip portion of the coseismic slip. We resolve the kinematic rupture process and HF radiation of the mainshock with a finite fault inversion method and a travel-time calibrated back-projection technique, respectively, where the travel time calibration was obtained by relocated aftershocks and historic events. The resolved mainshock rupture is characterized by a single slip patch located at the depth of 20-45 km, elongated ~100km parallel to the trench. The HF sources are distributed along the up-dip edge of the coseismic slip, within a belt that also contains refined seismicity, as well as the mainshock epicenter and the triggered HF sources of the Mw7.4 foreshock. Strong stress heterogeneity in this belt at the depth of 15-20 km is mostly likely caused by the beginning of serpentinization in the overriding oceanic mantle wedge. The abnormal event suggests re-evaluation of earthquake hazards in conventionally considered aseismic area.

Session: Earthquake Source Parameters: Theory, Observations and Interpretations

Type: Oral

Date: 4/18/2023

Presentation Time: 02:30 PM (local time)

Presenting Author: Hongyu Zeng

Student Presenter: Yes

Invited Presentation: 

Authors