SCEC Award Number 12127 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title INVESTIGATING ABSOLUTE STRESS IN SOUTHERN CALIFORNIA CONSTRAINED BY EARTHQUAKE FOCAL MECHANISMS AND MODELS OF STRESS CONTRIBUTIONS FROM TOPOGRAPHY AND FAULT LOADING
Investigator(s)
Name Organization
Bridget Smith-Konter University of Texas at El Paso Karen Luttrell United States Geological Survey David Sandwell University of California, San Diego
Other Participants Teira Solis (UTEP graduate student)
SCEC Priorities 2d, 1b SCEC Groups SDOT, Seismology, Geodesy
Report Due Date 03/15/2013 Date Report Submitted N/A
Project Abstract
 The 3-D orientation of the in situ stress field in Southern California is reflected in the focal mechanisms of moderate to large magnitude earthquakes. An extensive new catalog [Yang et al., 2012] contains 2310 high quality mechanisms from events with M>3 in this region indicating a heterogeneous stress field, with strike-slip, reverse, and normal faulting in close proximity to one another. We attempted to reconstruct these observations by accounting for the stress fields from three sources: 1) the 3-D crustal stress imposed by topography of the surface and Moho, as constrained by gravity observations; 2) the 3-D earthquake cycle stress accumulated on locked fault segments; and 3) a 2-D regional stress field representing plate boundary scale tectonic driving stress. Three primary findings have resulted from this work and form the basis of several avenues of future research: 1) We computed 3-D depth dependent stress components from models of local compensated topography and tectonic fault stress accumulation rate. These models were contributed to the SCEC Community Stress Model (CSM) Workshop (October 2012) for review and analysis. 2) Based on the 3-D stress from topography, we are able to identify absolute lower bounds on the regional stress magnitude of 30 MPa NNE principal compression and 10 MPa ESE principal tension. 3) We solved for the best-fitting fault segment loading times and found these to be low on the SAF and SJF, and high on the Elsinore and ECSZ, consistent with expected earthquake recurrence interval on each fault.
Intellectual Merit In this research we assess how well a combination of stresses from topography, fault loading, and plate boundary driving forces are able to match observed stress orientations from focal mechanisms in Southern California, and to subsequently constrain the absolute magnitude of the regional driving stress by determining bounds on which regional stress fields can satisfactorily match the observed stress orientations. Based on the 3-D stress from topography, we are able to identify absolute lower bounds on the regional stress magnitude of 30 MPa NNE principal compression and 10 MPa ESE principal tension. For each fault segment, a best-fitting loading time and 2-D driving stress was also found. The loading time was found to be generally low on the San Andreas and San Jacinto segments (~0-250 years) and high on the Elsinore and Eastern California Shear Zone faults (~1000 years). This is on the order of, or possibly longer than, the expected recurrence interval of each fault. These preliminary findings may indicate that faults are able to carry residual stress beyond an individual earthquake cycle.
Broader Impacts A component of this SCEC4 funded project emphasized Earth Science education and communication of pertinent and accessible earthquake information to the general public. Directly aimed at disseminating geoscience educational material to our local community, we worked closely with the UTEP Pathways to the Geosciences program to develop education content for our department’s high school summer camp program. Smith-Konter participated in several summer sessions UTEP Pathways Summer Camp for high school students, where she lead students through a series of hands-on experiments and educational activities centered on earthquakes and plate tectonics.
We have been actively sharing relevant research material with the UTEP Cyber-ShARE Center and SIO Visualization Center. Both centers have been coordinating activities with us to catalog relevant images, animations, and interactive 3-D visualization scene files. With the recent opening of the UTEP Visualization Center, we have also be able to collaborate with the Center’s interns and graduate students to develop interactive 3-D Fledermaus visualizations derived from our modeling efforts.
Exemplary Figure Figure 1