SCEC Award Number 25231 View PDF
Proposal Category Individual Research Project (Single Investigator / Institution)
Proposal Title Identifying seismicity bursts across California to probe fault-zone conditions
Investigator(s)
Name Organization
Wenyuan Fan University of California, San Diego
SCEC Milestones A1-2, B2-2, D1-1, D2-1, D2-2 SCEC Groups Seismology, FARM, SDOT
Report Due Date 03/15/2026 Date Report Submitted 03/27/2026
Project Abstract
 Earthquakes cluster in space and time. Seismicity bursts include many earthquakes occurring compactly in space and time. These bursts are likely caused by a cascade interaction of elastic fault ruptures among the earthquakes and/or additional forcing processes in the fault zones, such as fluids or aseismic slip. The sequence characteristics of such bursts are useful in studying the evolving fault-zone conditions and can provide new insights into earthquake nucleation and sequence development. In this proposal, we plan to develop and apply a novel statistical procedure to systematically identify seismicity bursts across California using state-of-the-art network catalogs and enhanced, high-resolution catalogs to comparatively study fault-zone conditions from Baja California to Cape Mendocino. Our central objective is to use the identified seismicity bursts to probe fault zone conditions, their associated temporal and spatial variations, and their physical causes. Our proposed efforts will offer a new dynamic perspective in both space and time on earthquake rupture and sequences. These findings have direct implications for large earthquake preparation and nucleation processes, aligning with the mission and milestones of SCEC.
Intellectual Merit This project systematically investigated seismicity bursts and the associated fault zone evolution in southern California. Through the development and application of a new data-driven statistical approach, we identified abundant and widespread highly clustered seismicity bursts throughout the region. The identified seismicity bursts provide valuable candidates for case studies to further investigate local fault zone processes, offering new opportunities to understand earthquake sequences at kilometer-scale spatial resolution and hour-scale temporal resolution. The methodology developed in this project is readily applicable to other regions with high-quality earthquake catalogs.
Broader Impacts This project supported PhD student Nicolas DeSalvio at SIO/UCSD. The study constitutes a core component of his doctoral thesis, in which he developed and applied the statistical burst identification method, conducted the comprehensive analyses of burst characteristics, and led the interpretation of the results. The project provided DeSalvio with extensive training in statistical seismology, earthquake source physics, and the analysis of large-scale seismological datasets.

DeSalvio, N. D., W. Fan, A. J. Barbour, and J. L. Hardebeck (2025), Compact Seismicity Bursts Have Different Characteristics from Regional Seismicity, Journal of Geophysical Research: Solid Earth, doi:10.1029/2025JB032917.
Project Participants Nicolas DeSalvio and Wenyuan Fan from SIO/UCSD, and Andrew Barbour and Jeanne Hardebeck from USGS.
Exemplary Figure Study area and locations of the identified seismicity bursts. (a) Number of seismicity bursts identified by the β-statistic. Inset shows the magnitude of completeness (Mc) and spatial extent of each grid. (b) Magnitude time series for a seismicity burst identified within the grid adjacent to the (b) label in panel (a), near Brawley, CA, on June 2, 2008. The burst lasts one day (shaded in blue); the seismicity rate change in the subsequent 24-hour period (shaded in purple) is not statistically significant. Seismicity bursts like this are abundant and widespread throughout southern California.
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