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Ensemble Analysis of Large Megathrust Earthquakes: From Rupture Heterogeneity to Stress Changes and Ground Motion

Description: 

Inferences about offshore megathrust earthquake processes are notoriously uncertain and sensitive to data choices and ad hoc regularization schemes, hampering quantitative interpretation. Here, we characterize the similarities and differences between several large earthquake models derived from unregularized Bayesian kinematic inference methods, including the 2011 M9.0 Tohoku, 2014 M8.1 Iquique, 2015 M8.3 Illapel, 2016 M7.8 Pedernales, and 2015 M7.8 Gorkha. Through finite-fault models derived from joint datasets and consistent inversion schemes, we assess relationships between kinematic rupture parameters, including slip, rupture speed, rise time, and average slip rate, locally and within and across events. We use posterior model ensembles to compute static surface deformation and on-fault stress changes, dynamic ground motion, and their spatiotemporal covariances. For posteriors, patch-level correlations are robust across some parameters, given expected trade-offs, but intra-event correlations between most parameters are variable across events. The discrepancies with theoretical predictions imply limitations in adopted physics and/or inversion approaches for heterogeneous rupture scenarios. Our analysis reveals characteristic deformation and stress change patterns over the megathrust, with uncertainty influenced by station coverage, fault slip patterns, and data-model error structure. Despite significant spatial variability in source properties, the static elastic strain drop is tightly constrained to ~100–300 microstrain, while the static stress drop spans ~5–25 MPa. Predicted peak ground displacements (PGD) exhibit near-field discrepancies with empirical scaling laws due to finite-source and directivity effects. Our findings inform physics-based earthquake modeling and improve quantification of rupture complexity and hazard impacts.

Session: Linking Subduction Zone Processes and Cascading Hazards in Alaska, Cascadia, Chile and Beyond [Poster]

Type: Poster

Date: 4/16/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Junle Jiang

Student Presenter: No

Invited Presentation: 

Poster Number: 139

Authors