SCEC Award Number 15201 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Paleo-seismic rupture rates for California
Investigator(s)
Name Organization
David Jackson University of California, Los Angeles Yan Kagan University of California, Los Angeles
Other Participants
SCEC Priorities 2b, 2a, 4e SCEC Groups WGCEP, CSEP, Seismology
Report Due Date 03/15/2016 Date Report Submitted 05/11/2016
Project Abstract
 We found in our previous project on this topic that recorded paleoseismic events used in the UCERF3 hazard report occured at an average exceeding 4 per century. However, none have occurred since 1910, a hiatus beyond the 99% confidence interval of the paleoseismic record. As we reported last year, possible explanations include extreme luck, unmodeled physical interaction between faults, or errors in the paleo- seismic data. In the most recent project we explored ways that physical models of earthquake interactions might explain the hiatus, presenting the results at the SCEC annual meeting, the American Geophysical Union, and the Seismological Society of America. We’ve consulted with scientists at UC Riverside who developed the RSQSim model for earthquake interactions. In spite of serious efforts, no solution was found, and the best explanation for the hiatus is that the rate of paleo-earthquakes before 1910 was seriously overestimated.

We’ve also examined the uncertainties and assumptions involved in estimating seismic moment rate from deformation data such as geodetic strain and fault slip rates. We’ve devised methods to estimate lognormal probability distributions for measured quantities presented as upper and lower limit values, and to combine the distributions of multiple factors to obtain an error distribution for the seismic moment rate. Results imply that moment rate estimates from surface deformation rates are larger than expected, and they should be used in earthquake forecasts with extreme caution.
Intellectual Merit SCEC develops earthquake probability models for use in hazard estimates such as UCERF3. In these projects, geological and seismological data are combined to give long-term earthquake rates. Internal consistency of the paleoseismic, geologic and geodetic data has not before been examined comprehensively. Using techniques developed for prospective testing by CSEP, we examined tested the whole set of paleo- seismic dates used in the UCERF3 report. The hiatus of the last century points to remarkable statewide clustering not previously recognized and not yet modeled, or to inconsistencies that could require corrections to UCERF3 earthquake rates. We’ve extended the range of models that can be rigorously tested to include those based on geological and geodetic data. Rigorous testing will take many decades or more, but we expect our grandchildren to be wresting with the same questions about future earthquakes.
Broader Impacts The project has involved graduate students Anne Strader and Deborah Weiser, both of whom developed important testing and statistical skills for their future careers. We’ve developed statistical procedures that can be applied in many fields including atmospheric sciences, astronomy, and engineering.

Presentation of results at SCEC meetings and AGU and SSA conferences has stimulated dialog among seismologists, geologists, and computational modelers of earthquake occurrence and interaction.
Exemplary Figure N/A
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