Slow and Go: Pulsing Slip Rates on the Creeping Section of the San Andreas Fault

Abstract:

Rising and falling slip rates on the creeping section of the San Andreas Fault have been inferred from variations of recurrence intervals of repeating micro-earthquakes, but this observation has not previously been confirmed using modern geodetic data. Here, we report on observations of this ‘pulsing’ slip obtained from advanced multi-temporal Interferometric Synthetic Aperture Radar (InSAR) data. The surface deformation time series show a strong correlation to the previously documented slip rate variations derived from repeating earthquakes on the fault interface, at various spatial and temporal scales. Time series analysis reveals a quasi-periodic pulsing with approximately 2-year-long intervals along some sections of the fault in both InSAR and repeating earthquake datasets, with the earthquakes on the fault interface lagging behind the far-field deformation by about six months. This suggests a temporal delay between the pulsing crustal strain generated by deep-seated shear and the time-variable slip on the shallow fault interface, and that at least in some places this process may be cyclical.