SCEC Award Number 17041 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Testing and Reconciling Stress Drop and Attenuation Models for Southern California
Investigator(s)
Name Organization
Rachel Abercrombie Boston University Peter Shearer University of California, San Diego
Other Participants Daniel Trugman, UCSD
SCEC Priorities 1d, 1c, 4a SCEC Groups Seismology, FARM, GM
Report Due Date 06/15/2018 Date Report Submitted 06/15/2018
Project Abstract
 This SCEC funded research involves systematic analyses to improve the quality and reliability of stress drop measurements in Southern California. Earthquake stress drop is a fundamental source parameter, implicit in many of SCEC science goals. It is relatively easy to estimate from seismic data, but hard to measure reliably and well. The large uncertainties and scatter in results affect strong ground motion prediction, and also limit our understanding of the physics of the earthquake rupture process, including distinguishing induced seismicity from natural seismicity. We are studying the complementary approaches of the two PIs to investigate sources of consistency and discrepancies, and quantify uncertainties in stress drop estimates. We made considerable progress on these goals during the last year by focusing on test regions near Cajon Pass and Landers. We find a strong correlation between the stress estimates computed using the different approaches, but with considerable scatter. We are currently working to isolate the sources of disagreement between the methods. Our longer-term aim is to develop an improved approach to estimate more accurate and reliable stress drops (SCEC4 Science Priorities 2a and 2d Q1), together with regional attenuation and site effects (SCEC4 Science Priority 6a).
Intellectual Merit Our research relates to many key SCEC objectives, including modeling earthquake source properties, evaluating the stress state of complex fault systems, constraining seismic radiation and scaling of earthquake source parameters, and improving high-frequency ground motion predictions.
Broader Impacts This project helps support graduate students at UCSD. Our research has implications for the state of crustal stress, fault heterogeneity and friction, and quantifying the importance of source spectral variations and crustal attenuation differences in high-frequency recordings. Ultimately this work will help researchers better understand earthquake physics and improve strong ground motion predictions.
Exemplary Figure Figure 3. Source spectral ratio comparison for 6 example events, showing spectra from individual event EGF (black), spectral decomposition ratios for target event with same set of EGFs (but not necessarily same stations), equal weighting per EGF (red) and EGFs weighted by number of stations in individual EGF ratios (blue). The titles show the target event ID, the number of EGFs and the total number of spectral ratios.