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 03/15/2024
Project Abstract
 INTERIM REPORT: Current progress: (1) completed new analysis of stress drop estimates of the 2012 swarm and Ridgecrest foreshocks. (2) preliminary analysis of foreshock stress interactions and spatiotemporal migration pattern. To do: synthesize three foreshock sequences to understand the differences and similarities between different types of sequences, and discuss the roles of "cascading failure" and "aseismic processes" in the triggering process. Anticipated completion date: fall 2021.
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.