Rummaging for repeaters: Building a California statewide repeating earthquake catalog

Norma A. Contreras, & Gareth J. Funning

Submitted August 30, 2026, SCEC Contribution #15593, 2026 SCEC Annual Meeting Poster #TBD

California contains numerous faults that exhibit aseismic slip (creep). In contrast to locked faults, which accumulate stress and can rupture in large, damaging earthquakes, creeping faults display velocity-strengthening behavior. As a result, they can hinder or even halt earthquake rupture (e.g., Harris 2017, Uchida & Bürgmann 2019). Constraining the rate and extent of creep is crucial for understanding a fault’s seismogenic potential and improving risk and hazard assessments. Geodetic measurements, e.g., InSAR or GNSS, can be used to estimate shallow creep. However, alternative methods are needed to estimate creep at depth. Repeating earthquakes (REs) are quasi-periodic, co-located earthquakes that are often associated with creeping faults and can be used to identify and estimate creep at depth. In this work, we build a RE catalog to identify creeping faults throughout California.

Our statewide RE catalog is built using the FARESearch (Fully-Automated Repeating Earthquake Search) algorithm (Funning and Shakibay Senobari 2021). This algorithm identifies REs based on waveform similarity, and uses a hierarchical clustering algorithm to group highly-correlated event pairs into larger RE sequences. Our catalog spans the years 1984-2022 and includes faults from the Mendocino triple junction down to the Imperial Valley. To identify RE sequences associated with long-term creep we identify quasi-period sequences following the methodology of Waldhauser and Schaff (2021). The slip per event and slip rates along a fault are estimated using the approach of Nadeau and Johnson (1998), using updated calibration parameters (Shakibay Senobari and Funning 2019).

We search for REs on 70+ faults across California over a 40-year period. During this time window, we identify 75,000+ candidate REs, which are grouped into 11,500+ RE sequences. Of these, 2,000+ are identified as quasi-periodic RE sequences. We identify a high quantity of REs along well-known creeping faults (e.g., the central San Andreas and Calaveras faults), as well as a few REs along faults that are not known to actively creep (e.g., the Garlock fault), which may indicate other source mechanisms for the REs. Preliminary estimates of fault slip rates using our RE fault catalogs agree with published work. As part of our future work, we will use RE-derived slip rates and invert for creep rates along California faults using a combination of seismic and geodetic data.

Key Words
repeating earthquakes, creep, aseismic slip

Citation
Contreras, N. A., & Funning, G. J. (2026, 08). Rummaging for repeaters: Building a California statewide repeating earthquake catalog. Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology