Metropolis–Hastings BEM Inference of Interseismic Coupling on the Kamchatka Subduction Zone and Its Connection to the 2025 Megathrust Earthquake

Axel J. Periollat, & Gareth Funning

Submitted September 7, 2025, SCEC Contribution #14847, 2025 SCEC Annual Meeting Poster #TBD

On July 30, 2025, a Mw 8.8 megathrust earthquake ruptured the central segment of the Kamchatka subduction zone, following a sequence of moderate foreshocks in the preceding weeks. This segment had remained seismically quiet since the last great Mw 9 earthquake in 1952, leaving a substantial interseismic gap. The 21 available GNSS velocities makes it difficult to accurately determine where and how interseismic strain is accumulating. This challenge calls for methods that can extract robust spatial patterns from sparse, noisy geodetic data without relying on overly restrictive assumptions.

To address this, we apply an objective Metropolis-Hastings Boundary Element Method (BEM) framework to infer the distribution of fault locking and creep prior to the 2025 earthquake without imposing prior constraints. This rare-opportunity—observing a megathrust only ~73 years after the previous one—allows us to spatially compare high-, moderate-, and low-probability locking zones with coseismic slip, providing a direct link between accumulated slip deficit and actual rupture distribution. We also compared our locking and slip-deficit patterns, resolved onto a high-resolution triangular fault mesh, with published coseismic slip models from the 1952 earthquake. These comparisons allow us to explore the potential mechanical and spatial connections between successive megathrust earthquakes.

Our ensemble-based approach enables exploration of a wide range of physically plausible patterns and their variability, revealing robust spatial heterogeneity and fine-scale locked-creeping transitions. Notably, the sequence of moderate foreshocks preceding the 2025 appear to have occurred within a stress shadow region adjacent to the strongly locked zone. The 2025 rupture nucleated within a zone of sustained strain accumulation, indicating that long-term interseismic locking at high spatial resolution can provide actionable insights into the spatial likelihood and potential sources of future large earthquakes.

Citation
Periollat, A. J., & Funning, G. (2025, 09). Metropolis–Hastings BEM Inference of Interseismic Coupling on the Kamchatka Subduction Zone and Its Connection to the 2025 Megathrust Earthquake. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)