SCEC Award Number 24176 View PDF
Proposal Category Collaborative Research Project (Multiple Investigators / Institutions)
Proposal Title How predictable are repeating earthquakes? Investigating controls on time-dependent variation in seismicity and slip rate on northern California faults
Investigator(s)
Name Organization
Gareth Funning University of California, Riverside Rachel Abercrombie Boston University
SCEC Milestones D1-1 SCEC Groups Seismology, SDOT, EFP
Report Due Date 03/15/2025 Date Report Submitted 03/21/2025
Project Abstract
 The goal of the project was to conduct an in-depth examination of spatiotemporal variations in repeating earthquake sequences to better understand how they respond to and reflect changes in loading rates, local seismicity, and nearby moderate (3.5≤M<5) events. Focusing on repeating earthquake sequences found on the Calaveras and central San Andreas faults, we identified repeating earthquake sequences apparently affected by nearby earthquakes – cases where there were changes in recurrence interval and/or event magnitude close to the time of larger earthquakes nearby – and examined these in greater detail. We find that repeating earthquake sequences on the Calaveras fault are mainly affected by the 1984 M6.2 Morgan Hill and 2007 M5.4 Alum Rock events. Sequences on the northern end of the central San Andreas fault (San Juan Bautista region) exhibit similar behavior. However, sequences on the southern end of the creeping San Andreas fault (Parkfield region) appear sensitive to much smaller (M3.5+) events, suggesting that the behavior of REs can provide insights into the sensitivity of a fault to external stress perturbations, and potentially to its likelihood of failure.
Intellectual Merit We seek to better understand interactions between earthquakes and their capability of one earthquake to trigger others. Earthquakes and the faults on which they occur do not exist in isolation and the dynamic and static stresses from even small nearby earthquakes can potentially influence the recurrence intervals of large, damaging earthquakes: stress-shadows can inhibit earthquake nucleation, while large magnitude events can result in clock advances for events in other areas.
Broader Impacts The periodicity of earthquakes and the factors that affect earthquake recurrence intervals are of crucial importance for risk and hazard assessments, as are the accurate delimitation of areas of major Californian faults that are undergoing aseismic creep.
Project Participants Gareth Funning (PI)
Rachel Abercrombie (PI)
Norma Contreras (Graduate Student)
Exemplary Figure Figure 4: RE sequence changes in recurrence interval (Tr) and magnitude for target events M3.5 to M<4.0 (magenta lines). Gray vertical lines denote M3.5-5 events within 3 km of the REs. Blue(red) circles denote an individual RE’s deviation from the mean magnitude(recurrence interval) for that sequence. Filled circles indicate a deviation greater than 1 standard deviation from the mean value. Dashed green lines denote the 1984 M6.2 Morgan Hill, 1989 M7.0 Loma Prieta, and 2007 M5.4 Alum Rock earthquakes.
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