Surface Creep Rate of the Southern San Andreas Fault Modulated by Stress Perturbations From Nearby Large Events

Abstract

A major challenge for understanding the physics of shallow fault creep has been to observe and model the long-term effect of stress changes on creep rate. Here we investigate the surface creep along the southern San Andreas fault (SSAF) using data from interferometric synthetic aperture radar spanning over 25 years (ERS 1992-1999, ENVISAT 2003, and Sentinel-1 2014. The main result of this analysis is that the average surface creep rate increased after the Landers event and then decreased by a factor of 2-7 over the past few decades. We consider quasi-static and dynamic Coulomb stress changes on the SSAF due to these three major events. From our analysis, the elevated creep rates after the Landers can only be explained by static stress changes, indicating that even in the presence of dynamically triggered creep, static stress changes may have a long-lasting effect on SSAF creep rates.Plain Language Summary There are two significant conclusions from this study. First, we analyzed 25 years of InSAR measurements over the Southern San Andreas Fault system to document a major increase in the average creep rate following the 1992 Mw 7.3 Landers Earthquake which is then followed by creep rate reductions after the 1999 Mw 7.1 Hector Mine Earthquake and the 2010 Mw 7.2 El Major Cucapah Earthquake. Second, we attribute all these creep rate changes to the Coulomb stress variations from these three major Earthquakes. The dynamic Coulomb stress changes are similar for all three events, contributing to triggered creep on the SSAF. In contrast, the static Coulomb stress changes on the SSAF are positive after the Landers and negative after the Hector Mine and El Major Cucapah, coinciding with the higher average creep rate after the Landers and lower rates after the other two events. An implication of this study is that small but steady Coulomb stress changes have a larger impact on shallow creep than the larger dynamic stress changes associated with passing seismic waves. These results illuminate the significance of time scale-dependent complexity of shallow fault creep and how these behaviors are communicated by stress perturbations from regional earthquakes.

Testing the Influence of Static and Dynamic Stress Perturbations On the Occurrence of a Shallow, Slow Slip Event in Eastern Taiwan

“…Static stress changes due to permanent fault displacements can trigger seismic or aseismic fault slip on nearby faults (Harris, ; King et al, ; Xu et al, ). To estimate a possible contribution of permanent change in static stress to the SSE, we model the Coulomb stress changes induced by the M w 6.2 Nantou mainshock on the receiver fault plane candidates of the SSE using Coulomb 3.4 (Lin & Stein, ; Toda et al, ).…”

“…Stress perturbations from a mainshock rupture can trigger spontaneous or delayed SSEs (over hours to months; e.g., Hayes et al, 2014;Hirose et al, 2012;Rolandone et al, 2018), which release stress that had built up during the previous inter-SSE interval (Bürgmann, 2018), and can also trigger transient creep (Lienkaemper et al, 1997;Wei et al, 2015) or modulate surface creep rate (Xu et al, 2018). In general, dynamic triggering of SSEs remains a rare phenomenon, and only a few cases are documented (Araki et al, 2017;Itaba & Ando, 2011;Wallace et al, 2017;Zigone et al, 2012).…”

Buried Aseismic Slip and Off‐Fault Deformation on the Southernmost San Andreas Fault Triggered by the 2010 El Mayor Cucapah Earthquake Revealed by UAVSAR

“…We depict a simplified boundary of the zone of hydrologic deformation in Figure 8 , based on Xu et al. ( 2018 ) and Lindsey et al. ( 2014 ).…”

“…The “Approximate margin of leakage” refers to the position of the edge of displacement that we identified using 5 interferograms of Xu et al. ( 2018 ) below the Coachella canal and the vertical data set of Lindsey et al. ( 2014 ).…”

“…Xu et al. ( 2018 ) examine 25 years of ERS, Envisat and Sentinel interferograms and detect rate changes on decadal scales, modulated by large earthquakes. They conclude static stress changes may cause this variation in shallow creep rates.…”