SCEC Award Number 21032 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Roles of foreshocks in triggering large earthquakes and stress drop validation
Investigator(s)
Name Organization
Xiaowei Chen University of Oklahoma
Other Participants Jiewen Zhang
SCEC Priorities 1d, 4a, 5a SCEC Groups Seismology, FARM
Report Due Date 03/15/2022 Date Report Submitted 11/05/2024
Project Abstract
 Improved earthquake location and stress drop estimation methods provide great details of
the stress drop spatial and temporal variations. Using an improved stacking-based spectral
estimation method, we analyzed the stress drop variations for the 2012 Brawley and the 2019 M7
Ridgecrest earthquake sequences. We account for depth-dependent attenuation variations by
solving for empirical correction spectrum for events of different depth. For the 2012 Brawley
sequence, we find strong geometrical control of stress drop distributions and temporal variations
after M5 earthquakes. For the 2019 Ridgecrest sequence, we thoroughly compared the corner
frequency and stress drop estimations using different choices of window length and frequency
bandwidth, and found variable influences of the result. The choice of window length and wave
type also influence the seismic moment estimations, which resulted in different scaling trends.
Intellectual Merit The research contributes to a better understanding of earthquake source processes and the preparation process for large earthquakes. We find different trends of “foreshock” stress drops for the M7.1 Ridgecrest earthquake and the M5 Brawley earthquakes. The low “foreshock” stress drop for Ridgecrest is consistently found using different wave types and different attenuation corrections. The consistency between the Ridgecrest foreshock and the three other M7 earthquakes in Chen & Shearer (2013) suggests a possible common precursory behavior for large earthquakes. However, the Brawley swarm exhibits more complicated temporal and spatial behaviors before and after M5 earthquakes, suggesting an influence of both internal and external processes. These new results have motivated collaboration between PI and Dr. Jiang to integrate modeling, geodetic observations and seismology to better understand earthquake swarms. The results for the Ridgecrest sequence contributed to the stress drop validation project, contributing to a better understanding of biases and uncertainties of earthquake source parameter estimations.
Broader Impacts The project results are beneficial for learning earthquake hazards, risks and earthquake physics. The project enabled PI to continue collaborating with former postdoc scholar Qimin Wu, contributed to the training and education of students at the University of Oklahoma, and initiated new collaboration with an earthquake modeler. This project also supported PI Chen’s participation in the Stress drop validation project on the Ridgecrest sequence.
Exemplary Figure Figure 4 shows the foreshock and aftershock stress drop variations. The consistent difference between Ridgecrest and other M7earthquakes suggest common triggering process for large earthquakes.
Linked Publications

Add missing publication or edit citation shown. Enter the SCEC project ID to link publication.