Updated California Aftershock Parameters

Jeanne L. Hardebeck, Andrea L. Llenos, Andrew J. Michael, Morgan T. Page, & Nicholas J. van der Elst

Published August 9, 2018, SCEC Contribution #8361, 2018 SCEC Annual Meeting Poster #047

Reasenberg and Jones (Science, 1989) introduced a statistical model for aftershock rate following a mainshock, along with estimates of "generic" California parameter values based on past aftershock sequences. The Reasenberg and Jones (1989) model has been used for decades to issue aftershock forecasts following M≥5 mainshocks in California. Here we update the "generic" parameters for California through a fit to the aftershock sequences of M≥5 mainshocks occurring since 1980. We find aftershock productivity values that are lower on average than the generic productivity reported by Reasenberg and Jones (1989), likely because low-productivity sequences were omitted from their analysis. We confirm the observation of Llenos and Michael (SRL, 2017) that southern California sequences are more productive on average than northern California sequences. The Mendocino area is much less productive, while the hydrothermal areas in Long Valley, Coso, and the Salton Sea, in contrast, are much more productive. We also quantify the variability of the Reasenberg and Jones (1989) productivity parameter a between sequences with a normal distribution. This distribution of a-values can be used to compute aftershock forecasts that include epistemic uncertainty, and can be used as the prior for Bayesian updating of the a-value as a sequence progresses (e.g. Page et al., BSSA, 2016).

Citation
Hardebeck, J. L., Llenos, A. L., Michael, A. J., Page, M. T., & van der Elst, N. J. (2018, 08). Updated California Aftershock Parameters. Poster Presentation at 2018 SCEC Annual Meeting.

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