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

Monday, 15 December 2014: 9:15 AM
Ryan C Turner1, Manoochehr Shirzaei2, Robert M Nadeau1 and Roland Burgmann1, (1)Univ California Berkeley, Seismological Laboratory, Berkeley, CA, United States, (2)Arizona State University, Tempe, AZ, United States
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.