UC San Diego

Abstract The Southern San Andreas fault (SSAF) in the Coachella Valley experiences shallow creep and slow slip events (SSE), which re‐distribute stresses in the seismogenic zone and affect the potential of future earthquakes. Although average creep rates are relatively well‐constrained, untangling the details of spatiotemporal variation in creep along the SSAF has been challenging due to limited data coverage. In this study, we use 7 years of Interferometric Synthetic Aperture Radar data from the dense Sentinel‐1 catalog to image and model the evolution of shallow creep along the SSAF. We generate time series of fault parallel displacements and isolate the signal associated with shallow creep. We apply a network inversion filter approach to invert the surface displacements for the full slip history on the shallow creeping part of the SSAF and simultaneously characterize model uncertainties. Although some quasi‐steady creep may have been occurring at the southern end of the SSAF prior to 2017, the slip history during 2015–2021 is dominated by a multi‐year SSE where the elevated creep rate along nearly the entire SSAF was dynamically triggered by the 2017  8.2 Chiapas earthquake. The SSE exhibited pulse‐like bilateral propagation, with the total moment release equivalent to a  5.2 earthquake. The dynamic triggering and the subsequent slow fall‐off of slip and moment rate are suggestive of the low fault strength and healing rates. Plain Language Summary The San Andreas fault in Southern California exhibits unsteady shallow creep in the top 2–3 km. One of the largest shallow slip episodes was triggered on the Coachella Valley section of the Southern San Andreas fault (SSAF) in 2017 by a magnitude 8.2 earthquake that occurred as far as 3,000 km away in Mexico. We use radar data collected by orbiting satellites to measure minute ground motions due to shallow creep on the SSAF, and invert the observed ground motion for the history of shallow slip on the SSAF. We find that the 2017 accelerated slip episode started in the central part of the Coachella Valley segment of the SSAF, and then propagated bi‐laterally over a distance of about 10 km in each direction. This slow slip event lasted for more than a year, and released mechanical energy equivalent to a magnitude 5+ earthquake. Key Points Sentinel‐1 interferometry images 40+ mm of shallow creep on the SSAF between 2017 and 2021, equivalent to a  5.2 earthquake Transient shallow creep has propagated bi‐laterally after being triggered by the 2017  8.2 Chiapas earthquake The observed slip history is suggestive of low strength and slow healing of the shallow creeping part of the SSAF