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Constraining the Coseismic Slip Distribution of a Megathrust Earthquake by Stress-driven Afterslip

Description: 

Accurate determination of coseismic slip distributions is crucial for understanding earthquake physics and assessing seismic hazards. However, inversions using only coseismic data often yield highly variable slip models. While these uncertain slip models are routinely used to study postseismic processes, the physical coupling between coseismic stress changes and subsequent afterslip is rarely exploited to constrain the earthquake rupture itself.

Here, we develop an Ensemble Kalman joint inversion method that incorporates stress-driven afterslip to better constrain the coseismic slip distribution. Applied to the 2020 Mw 7.8 Simeonof earthquake using multiple geodetic datasets spanning one year, our method simultaneously solves for both coseismic slip and stress-driven afterslip.

The joint inversion reveals that the Simeonof rupture area is more compact than most previous models suggest, with a distinct velocity-strengthening barrier separating it from the 2021 Mw 8.2 Chignik earthquake rupture zone. This velocity strengthening barrier hosts almost zero coseismic slip but a significant amount of afterslip, and was obscured in coseismic-only models due to its small scale and smoothing constraints. The stress-constrained coseismic slip model together with its afterslip provides a physically consistent relationship with the relocated slab interface aftershocks, which prefer to occur where the afterslip stress is positive.

Session: Linking Subduction Zone Processes and Cascading Hazards in Alaska, Cascadia, Chile and Beyond - III

Type: Oral

Date: 4/16/2026

Presentation Time: 04:45 PM (local time)

Presenting Author: Zechao Zhuo

Student Presenter: Yes

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