SCEC Award Number 24157 View PDF
Proposal Category Individual Research Project (Single Investigator / Institution)
Proposal Title Influence factors of earthquake swarm evolution patterns across the SAFs
Investigator(s)
Name Organization
Xiaowei Chen Texas A&M University
SCEC Milestones D1-1 SCEC Groups Seismology, FARM, EFP
Report Due Date 03/15/2025 Date Report Submitted 04/10/2025
Project Abstract
 Earthquakes strongly cluster in space and time, and there are two major types of clustering: mainshock-aftershocks and earthquake swarms. Aftershock sequences are mainly driven by rapid stress change caused by the mainshock; however, the evolution of earthquake swarms is more complicated. In this proposal, we refer to earthquake sequences that do not follow the typical mainshock-aftershock sequences as swarms, which may include some foreshock-mainshock-aftershock sequences. Earthquake swarms and foreshocks can be driven by fluid-pressure propagation or aseismic slip, and influenced by earthquake interactions.
In this study, we investigated the clustering behaviors in southern California and northern California using relocated catalogs from 2019 to 2024. We use two different implementations of the nearest-neighbor approach developed by Zaliapin & Ben-Zion, (2013). We compare the clustering results with and without magnitude dependence, and then examine the difference in clustering behaviors between southern and northern California.
Intellectual Merit This project evaluated two different implementations of the nearest neighbor clustering approach in Python and Matlab, and identified strength and advantages associated with each method. We also evaluated the sensitivity of the clustering results to the choice of magnitude dependence. Specifically, we found that more swarm-like clusters are identified without magnitude dependence. The results exhibits systematic differences in cluster duration between North and Southern California, and clusters with low effective stress drops in Northern California. Such difference may reflect the differences in crustal rheology in different regions.
Broader Impacts This project supported two graduate students, and promoted collaboration between students. The comparison motivated current effort to develop more robust cluster identification implementation.
Project Participants Xiaowei Chen, Student Ahmad Mohammadi, Student Saeed Montazeri
Exemplary Figure Figure 9. Comparison of cluster parameters between northern and southern California. Northern California features larger nearest neighbor distances than southern California, and the average radius and duration for clusters of similar maximum magnitude are larger. Longer duration could reflect slower stress transfer process within the cluster. There are some clusters with relatively low effective stress drop in northern California, potentially related to creeping behaviors.
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