SCEC Award Number 14165 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title INTEGRATED STATIC AND DYNAMIC STRESS MODELING FOR INVESTIGATING TREMOR SOURCE REGIONS
Investigator(s)
Name Organization
Hector Gonzalez-Huizar The University of Texas at El Paso Bridget Smith-Konter The University of Texas at El Paso Aaron Velasco The University of Texas at El Paso Karen Luttrell Louisiana State University
Other Participants
SCEC Priorities 2d, 1b, 1c SCEC Groups CS, Transient Detection, Seismology
Report Due Date 03/15/2015 Date Report Submitted 01/08/2017
Project Abstract
 Under this project, we investigated the stress and frictional conditions of the SAF where tectonic tremor are dynamically triggered (by seismic waves) using numerical models of stresses. We studied the local static stress, and the dynamic stresses caused by passing triggering seismic waves from remote earthquakes. Dynamic stresses are modeled directly from recorded seismic signals, and static stress were obtained and modeled from existing SCEC Community Stress Model (CSM) contributions. We also investigate whether tremor signal characteristics (e.g. amplitude, duration, and frequency) can be used as a proxy to the local stress conditions where these are generated. Seismograms from more than 200 global earthquakes, with magnitudes equal or greater than 7, and occurred since 2000 to the present, were collected and visually inspected for triggered tremor. New cases of triggered tremor have been detected and triggering seismic waves have been modeled. Our preliminary results suggest that the average coefficient of friction at triggered tremor’s source regions is =1.90.5 in Northern California, =1.40.4 for Central California, and =2.10.6 for Southern California. Products resulting from this grant include 2 papers (one of which is progress) and 4 meeting presentation.
Intellectual Merit We presented a new approach for estimating the coefficient of friction in faults where tremor are triggered by the passing of seismic waves from remote earthquakes. This approach is based on the local tectonic stress and the stress changes generated during the passing of the triggering seismic waves from remote earthquakes. We identify new cases of tremor dynamically triggered along the SAF in California. Our preliminary results suggest that the average coefficient of friction at triggered tremor’s source regions is about 1.90 in Northern California, about 1.40 for Central California, and about 2.10.6 for Southern California.
Broader Impacts Dr. Gonzalez‐Huizar is a Hispanic Junior Investigator, and this project supported his effort during summer months. We are also training a UTEP doctoral student Sandra Hardy who is working in the analysis and modeling of the seismic data. UTEP is a major Hispanic Serving Institute (HIS), thus, the research and educational material resulting from this project directly influence traditionally underrepresented minorities.
Exemplary Figure Figure 3.

(a) Earthquakes M≥7.0 occurred since 2000 to present (about 200 mainshocks) investigated as potential triggers of tremor in the SAF. (b) Present-day earthquake cycle stress accumulation near locked fault segments in the SAF caused by the interseismic stress accumulation, coseismic stress drop, and postseismic stress relaxation over the last 1500 years on the SAF [Smith-Konter and Sandwell, 2009]. Listed are recent large earthquakes that have been reported to trigger tremor along the SAF system. In red-color are listed some of our new findings of cases of dynamically triggered tremor by global earthquakes. (c) Average coefficient of friction estimated for three broad geographic regions. Coefficient of friction was calculated as the rate between the absolute shear (static+dynamic) and absolute normal (static+dynamic) stresses acting at the moment when failure (sliding) occurs. Each dot corresponds to the value calculated from an individual triggered tremor pulse. Large circles are the average calculated for each region. Errors bars represents the standard deviation.

Gonzalez-Huizar et al., 2017
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