SCEC Award Number 15081 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title A systematic measurement of shear wave anisotropy in southern California
Investigator(s)
Name Organization
Zhigang Peng Georgia Institute of Technology
Other Participants Zefeng Li
SCEC Priorities 1a, 2d, 4a SCEC Groups Seismology, SDOT, FARM
Report Due Date 03/15/2016 Date Report Submitted 03/14/2016
Project Abstract
 We systematically measure shear wave splitting (SWS) parameters near the San Jacinto Fault Zone in southern California [Li et al., 2015]. The analyzed data consist of 86 permanent and temporary stations during 2012-2014, including five linear dense arrays crossing the SJFZ at different locations, and other autonomous stations within 15 km from the main fault trace. Shear phase arrivals and SWS pa-rameters (fast directions and delay times) are obtained with automated methods. Multiple criteria are then applied to rule out low-quality measurements, resulting in 23,000 high quality ones. We observe that the stations on the SW side have fast directions consistent overall with the maximum horizontal compression direction, while stations on the NE side show mixed patterns likely reflecting lithological/topographic variations combined with fault zone damage. There are no significant temporal changes of the fast direction and delay times within the study period. To extend this analysis to wider spatial and temporal span, i.e., the entire southern California from 1995 to 2014, we are making efforts to construct a platform for complete automated SWS analysis from fetching seismic data online to reporting the SWS measurements.
Intellectual Merit This project contributes to a better understanding of spatio-temporal evolutions of fault zone structures, as well as varying stress fields in southern California.
Broader Impacts This project provided partial support to graduate student Zefeng Li’s development of automatic shear wave split-ting measurement (Li et al., JGR, 2015), as well as P and S wave phase picker (Li et al., SRL, submitted). These techniques will be shared freely to other researchers to perform similar research. In addition, we plan to share the final shear wave splitting measurements for entire southern California data set once they are done.
Exemplary Figure Figure 3 Summary of the dominant fast directions and average delay times observed at all stations along the San Jacinto Fault Zone. The gray lines mark the active faults. Black bars are oriented along the dominant fast directions and scaled by the average delay times. Blue bars denote the orientations of maximum horizontal compressive directions from the stress model of Yang and Hauksson [2013]. The five boxes show the zoom-in plots for the five arrays. Gray bars show fast directions with resultant length less than 0.2, indicating poor concentration of fast directions. After Li et al. [2015].
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