Spatiotemporal variations of surface deformation, shallow creep rate, and slip partitioning between the San Andreas and southern Calaveras Fault

Abstract

The Calaveras Fault (CF) branches from the San Andreas Fault (SAF) near San Benito, extending sub-parallel to the SAF for about 50 km with only 2-6 km separation and diverging northeastward. Both the SAF and CF are partially coupled, exhibit spatially variable aseismic creep and have hosted moderate to large earthquakes in recent decades. Understanding how slip partitions among the main fault strands of the SAF system and establishing their degree of coupling is crucial for seismic hazard evaluation. We perform a timeseries analysis using more than 5 years of Sentinel-1 data covering the Bay Area (May 2015-October 2020), specifically targeting the spatiotemporal variations of creep rates around the SAF-CF junction. We derive the surface creep rates from cross-fault InSAR timeseries differences along the SAF and CF including adjacent Sargent and Quien Sabe Faults. We show that the variable creep rates (0-20 mm/yr) at the SAF-CF junction are to first order controlled by the angle between the fault strike and the background stress orientation. We further examine the spatiotemporal variation of creep rates along the SAF and CF and find a multi-annual coupling increase during 2016-2018 the subparallel sections of both faults, with the CF coupling change lagging behind the SAF by 3 to 6 months. Similar temporal variations are also observed in both b-values inferred from declustered seismicity and aseismic slip rates inferred from characteristic repeating earthquakes. The high correlation of b-value and slip-rate changes may indicate that the SAF is extremely sensitive to small stress perturbations. Hosted fileessoar.10512336.1.docx available at https://authorea.com/users/540230/articles/600165spatiotemporal-variations-of-surface-deformation-shallow-creep-rate-and-slippartitioning-between-the-san-andreas-and-southern-calaveras-fault Spatiotemporal variations of surface deformation, shallow creep rate, and slip partitioning between the San Andreas and southern Calaveras Fault

Space–Time Asymmetry in Earthquake Pairs along the Central San Andreas Fault: Evidence for Small Earthquake Links at Long Distances

“…Nadeau and McEvilly (2004) identified clusters of repeating earthquakes along the CSAF with variations in repeat times that suggest quasi-periodic variations in deep slip rate, assuming a model in which repeating earthquakes are driven by adjacent aseismic regions with slip that repeatedly loads the rupture region to failure. Li et al (2022) found a correlation between changes in deep slip rate along the CSAF inferred from similar earthquake repeat times and InSAR measurements of surface creep rate.…”

“…Although the long-term average creep rate has been nearly constant since 1970 (Ryder and Bürgmann, 2008), creepmeters have detected numerous individual creep events with durations of hours to days (e.g., Gittins and Hawthorne, 2022). InSAR analyses have also suggested temporal changes in creep rate at time scales of months to years (Khoshmanesh et al, 2015;Khoshmanesh and Shirzaei, 2018), some of which appear to have a seasonal component (Li et al, 2022). The CSAF is characterized by active seismicity with over 40,000 earthquakes recorded by the Northern California Seismic Network (NCSN) since 1981.…”