SCEC Award Number 15065 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Seismicity, Swarms, and Strain Changes in Southern California
Investigator(s)
Name Organization
Peter Shearer University of California, San Diego
Other Participants graduate student (to be named)
SCEC Priorities 2c, 2c, 2d SCEC Groups Seismology, Transient Detection, EFP
Report Due Date 03/15/2016 Date Report Submitted 03/14/2016
Project Abstract
 This SCEC funded research involves continued analysis of earthquakes recorded by the Southern California Seismic Network (SCSN). This has led to greatly improved earthquake locations, focal mechanisms, and estimates of stress drop. We are now using these products to perform integrated studies of seismicity and address a number of issues related to seismic hazard. We have recently focused on studying earthquake triggering models and their relationship to swarms and foreshock sequences. We have identified several aspects of the space/time clustering of seismicity that cannot be explained with standard (i.e., ETAS) triggering models, including details of the foreshock and aftershock behavior for small earthquakes. In particular, we have found that a significant fraction of small earthquake clustering is swarm-like and probably caused by underlying physical drivers, such as fluid flow or slow slip. We have now begun a systematic analysis of swarms in southern California, beginning with the development of a new swarm detection algorithm. Our results show that swarms are heterogeneously distributed in time and space and are likely related to foreshock sequences in some regions.
Intellectual Merit Our research relates to many key SCEC objectives, including characterizing seismicity clustering and its implications for earthquake prediction. Our main contribution has been to systematically and objectively examine large amounts of earthquake data, including swarms and foreshock sequences, to test whether existing models of earthquake clustering are adequate to explain the observations.
Broader Impacts This project helped support postdoc Qiong Zhang. Our research will help quantify earthquake clustering and triggering in southern California, which has broad implications for earthquake forecasting and predictability. Advances in these areas would have clear societal benefits.
Exemplary Figure Figure 2. Map view of the detected swarm (solid circle) events in the SJFZ. The circles are color-coded by occurrence time and scaled with the total number of events in each group. Hexagons represent the swarms identified from Vidale and Shearer (2006). Stars mark five M ≥ 5 earthquakes including two Superstition Hills in 1987 and three occurring south of Anza. Blue line shows the strike of the SJFZ. Grey dots denote the 77,377 catalog events between 1981 and 2014. CCF: Coyote Creek Fault. Note that the events shown on the map are only SJFZ events, and the events in surrounding faults are masked. From Zhang and Shearer (2016).