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Testing Rate-and-State Predictions of Aftershock Decay

Morgan T. Page, & Nicholas J. van der Elst

Submitted September 10, 2023, SCEC Contribution #13099, 2023 SCEC Annual Meeting Poster #157

We analyze aftershocks of the 2019 M7.1 Ridgecrest mainshock to test predictions made by the rate-and-state friction model of Dieterich (1994). Rate-and-state friction predicts that the seismicity rate after a stress step follows Omori decay, where the Omori c-value, which is the saturation in aftershock rate observed at small times, is larger for smaller stress steps. Put in the context of an aftershock sequence, this predicts that the Omori c-value will be systematically larger at greater distances from the mainshock. To our knowledge, this predicted effect has not been observed. In part this may be because the Omori c-value is difficult to measure, as it often reflects short-term catalog incompleteness in the mainshock coda rather than true saturation in aftershock rate. Some have even hypothesized that the true c-value may be zero, or as Kagan and Houston (2005) argued, negative.

We explore the dependence of the Omori c-value on the distance to the mainshock by applying the “a-positive” method (van der Elst and Page, submitted) to Ridgecrest aftershocks. This method is insensitive to short-term aftershock incompleteness and allows resolution of the true aftershock rate deep into the mainshock coda.

Key Words
aftershocks, Omori Law, statistical seismology, rate-state friction

Page, M. T., & van der Elst, N. J. (2023, 09). Testing Rate-and-State Predictions of Aftershock Decay. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)