Group , Poster #252, Earthquake Forecasting and Predictability (EFP)

Re-evaluation of the role of static stress triggering for aftershocks following the Ridgecrest, California earthquake sequence considering receiver plane uncertainty

Catherine Hanagan, Richard A. Bennett, & Amanda N. Hughes
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Poster Presentation

2021 SCEC Annual Meeting, Poster #252, SCEC Contribution #11287 VIEW PDF
Static stress transfer from preceding earthquakes is commonly invoked as the primary mechanism for triggering aftershocks, but evaluation of this mechanism depends on aftershock rupture plane orientations and hypocenter locations, which are often subject to significant observational uncertainty. We evaluate static failure stress for an unusually large dataset comprising 2,888 aftershocks following the 2019 Ridgecrest, California earthquake sequence. We compare failure stress resolved on published aftershock focal planes and planes that are optimally oriented (OOPs) in the regional and earthquake perturbed stress field. Like previous studies, we find that failure stress resolved on OOPs predi...cts a higher percentage (96%) of triggered aftershocks relative to that predicted when using nominal aftershock rupture planes (65-78%), independent of how focal plane ambiguity is resolved. Further, observed aftershock focal planes appear to be statistically distinct from OOPs. Observed rupture planes, at least for larger magnitude events (M>3), appear to align more closely with pre-existing structure. Accounting for observational uncertainty associated with focal plane ambiguity, rupture plane orientation, and, to second order, aftershock locations permits a larger percentage of aftershocks to have potentially been triggered by static stress change, such that we cannot exclude static stress as the triggering mechanism for nearly all of the aftershocks considered in our study, particularly those further than 5 km from the modelled rupture planes. Dynamic stresses, afterslip, pore fluids, and other sources of unresolved small-scale heterogeneity in the post-mainshock stress field may also contribute appreciably to the occurrence of aftershocks closer to the mainshock.
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