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Characterizing Aftershock Dynamics in the Pacific Northwest Using Bayesian Etas

Description: 

The Pacific Northwest (PNW) has substantial earthquake risk, both due to the Cascadia megathrust fault and other fault systems under the region’s population centers. Forecasts of aftershocks following future large earthquakes will thus be desirable and require statistical models calibrated to a catalog of the PNW’s past earthquakes and aftershock sequences. This is complicated by the fact that the PNW contains multiple tectonic regimes hypothesized to have different aftershock dynamics as well as frequent swarms. We use the Epidemic-Type Aftershock Sequence (ETAS) model to describe the characteristics of earthquakes and aftershocks for the PNW, accounting for these different types of seismicity. Typically, maximum likelihood estimation (MLE) is used to fit ETAS to an earthquake catalog; however, the ETAS likelihood suffers from flatness near its optima, parameter correlation and numerical instability, making likelihood-based estimates far from robust. We present a Bayesian procedure for ETAS estimation, such that parameter estimates and uncertainty can be robustly quantified, even for small and complex catalogs like the PNW. We model the earthquakes of the continental PNW, using a new catalog formed by algorithmically combining US and Canadian data sources and then identifying earthquake swarms. We perform a completeness analysis that supports two complete subcatalogs split by latitude, and with differing start years and magnitudes of completeness. While ETAS parameter MLEs are unstable and depend on both the optimization procedure and its initial values, Bayesian estimates are insensitive to these choices. Bayesian estimates also fit the subcatalogs better than do MLEs. We use the Bayesian method to rigorously estimate ETAS parameters and their uncertainty when including swarms in the model, modelling across different tectonic regimes and complete subcatalogs, as well as from catalog measurement error. Many parameter estimates change substantially when considering these catalog issues, indicating their importance for seismicity rate modelling and aftershock forecasting in the PNW.

Session: Constraining Seismic Hazard in the Cascadia Subduction Zone [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Max Schneider

Student Presenter: No

Invited Presentation: 

Authors