Searching for Transient Slow Slips Along the San Andreas Fault Near Parkfield Using Independent Component Analysis

Abstract

The Parkfield segment of the San Andreas Fault (SAF) sits at the transition between the locked Cholame segment to the South and the SAF creeping segment to the North. The Parkfield segment hosts regular ~M_W 6 earthquakes followed by postseismic deformation. Recent studies based on geodetic data have highlighted spatial and temporal variations of aseismic slip rate in addition to postseismic slip along this section of the fault. We combine Global Navigation Satellite Systems (GNSS) and seismicity data over the 2006–2018 period to detail a comprehensive picture of transient slip events. We produce a catalog of relocated seismicity and repeating earthquakes. We use a variational Bayesian independent component analysis decomposition on GNSS data to separate geodetic deformation due to non-tectonic sources from signals of potential tectonic origin. We then reconstruct the temporal evolution of fault slip and detect potential slip transients. Those events, determined as mostly aseismic with the exception of one related to a M_W 4.8 earthquake, occur more frequently during the 2004 M_W 6 post-seismic period than during the subsequent inter-seismic phase. Our study illustrates the rich dynamics of seismic and aseismic slip during both post- and inter-seismic periods along active faults.