Using repeating earthquake sequences and geodetic data to build a statewide creep rate model

Norma A. Contreras, & Gareth J. Funning

Submitted September 7, 2025, SCEC Contribution #14884, 2025 SCEC Annual Meeting Poster #TBD

California is home to a variety of major faults that pose threats to the local populations. Several of these major faults, such as the central San Andreas fault, exhibit creep (aseismic slip), either fully or partially. This creeping behavior can be explained by velocity strengthening friction in the creeping areas of the fault surface, and can reduce the amount of strain that accumulates, and potentially inhibit both earthquake nucleation and rupture propagation along creeping faults. To improve seismic hazard estimates it is therefore essential to understand both the extent and rate of creep along faults.

In this study, we aim to build a statewide creep rate model for all California faults using a joint geodetic and seismic slip rate inversion. To estimate surface creep, we utilize geodetic measurements such as InSAR, GNSS, and alinement arrays. These methods, however, have poor depth resolution and may be hindered by sparse data coverage, particularly in remote or forested areas. Therefore, to estimate creep at depth, we use repeating earthquakes (REs), collocated and quasi-periodic earthquakes with nearly identical waveforms. These earthquakes are often found along creeping faults and can be used to identify areas of creep. We identify RE sequences using our FARESearch (Fully-Automated Repeating Earthquake Search) code, which identifies REs based on waveform similarity and hierarchical clustering (Funning and Shakibay Senobari, 2021; Shakibay Senobari and Funning, 2019). For a preliminary estimate of the creep rate distribution, we represent our target creeping faults as dislocations in an isotropic elastic half-space and invert for the slip rates on these, using our geodetic data (appropriately downsampled) and repeating earthquake sources as data points.

As the first part of our project, we have compiled a repeating earthquake catalog that spans from 1984 to 2022, covers over 15 faults and contains over 64,000 candidate REs. As a preliminary test, we invert for creep rates on the creeping central segment of the San Andreas fault, spanning from San Juan Bautista to Parkfield. Future work includes identifying REs on remaining California faults. Additionally, we will refine our inversion and develop a workflow that can be readily applied to all California faults.

Key Words
repeating earthquakes, San Andreas, creep, aseismic slip

Citation
Contreras, N. A., & Funning, G. J. (2025, 09). Using repeating earthquake sequences and geodetic data to build a statewide creep rate model. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)