SCEC Award Number 11005 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title California Earthquake Rupture Models
Name Organization
David Jackson University of California, Los Angeles Yan Kagan University of California, Los Angeles
Other Participants
SCEC Priorities A4, A9, A6 SCEC Groups EFP, SHRA, Seismology
Report Due Date 02/29/2012 Date Report Submitted N/A
Project Abstract
We present a stochastic earthquake source model for intermediate-to long-term forecasts. The model is based on fundamental observations: the frequency-magnitude distribution, slip rates on major faults, long-term strain rates, and source parameter values of instrumentally-recorded and historic earthquakes. The basic building blocks of the model are two pairs of probability density maps. The first pair consists of smoothed seismicity and weighted focal mechanisms based on observed earthquakes. The second pair contains the same type of information for faults. We construct from the model a “stochastic event set”, i.e. a large set of simulated earthquakes that are relevant for seismic hazard calculations and model testing. Their complete descriptions are determined in the following order: magnitude, epicenter, moment tensor, length, displacement, and down-dip width. Our approach assures by construction that the simulated magnitudes are consistent with the observed frequency-magnitude distribution. We employ a magnitude-dependent weighting procedure that tends to place the largest simulated earthquakes near major faults with consistent focal mechanisms. Nevertheless, our stochastic model allows for surprises, such as large off-fault earthquakes, which comply with the observation that several recent destructive earthquakes occurred on previously unknown fault structures. We apply the model to California to illustrate its features.
Intellectual Merit We've invented a new way to forecast earthquake occurrence employing a stochastic description of faults and adapting seismicity smoothing for use in fault smoothing as well. The method guarantees by construction that the forecast magnitude distribution is consistent with the observed regional distribution, it forecasts focal mechanisms, it allows for earthquakes to occur near rather than exactly on faults, and it obviates the need to assign earthquakes to specific faults.
Broader Impacts The developed method can be used by engineers and decision makers to estimate earthquake hazards and to compute theoretical seismograms with appropriate probabilistic weighting.
This project provided technical experience and training to undergraduate student Xiaohua Xu from USTC (China), Stefan Hiemer, a graduate student from ETH Zurich, and to UCLA graduate students Qi Wang and Anne Strader.
Exemplary Figure Figure 1: Normalized spatial rate density maps: (a) based on the earthquake catalog, and (b) based on the fault moment rate point sources. The logarithmic color scaling is mutually consistent for both maps.