Stress Changes on the Garlock fault during and after the 2019 Ridgecrest Earthquake Sequence

Abstract

The recent 2019 Ridgecrest earthquake sequence in Southern California jostled the seismological community by revealing a complex and cascading foreshock series that culminated in a M7.1 mainshock. But the central Garlock fault, despite being located immediately south of this sequence, did not coseismically fail. Instead, the Garlock fault underwent post-seismic creep and exhibited a sizeable earthquake swarm. The dynamic details of the rupture process during the mainshock are largely unknown, as is the amount of stress needed to bring the Garlock fault to failure. We present an integrated view of how stresses changed on the Garlock fault during and after the mainshock using a combination of tools including kinematic slip inversion, Coulomb stress change, and dynamic rupture modeling. We show that positive Coulomb stress changes cannot easily explain observed aftershock patterns on the Garlock fault, but are consistent with where creep was documented on the central Garlock fault section. Our dynamic model is able to reproduce the main slip asperities and kinematically estimated rupture speeds (≤ 2 km/s) during the mainshock, and suggests the temporal changes in normal and shear stress on the Garlock fault were greatest near the end of rupture. The largest static and dynamic stress changes on the Garlock fault we observe from our models coincide with the creeping region, suggesting that positive stress perturbations could have caused this during or after the mainshock rupture. This analysis of near-field stress change evolution gives insight into how the Ridgecrest sequence influenced the local stress field of the northernmost Eastern California Shear Zone.

Multifault Models of the 2019 Ridgecrest Sequence Highlight Complementary Slip and Fault Junction Instability

“…These complexities pose challenges in understanding the rupture physics and regional hazard assessments. Using fault geometry assumptions based on surface traces and aftershock patterns, investigations of the Ridgecrest rupture processes and slip distributions have formed a consensus that the M w 6.4 foreshock ruptured a NE‐SW fault segment, followed by the M w 7.1 mainshock occurring on the ~40 km NW‐SE striking fault (Barnhart et al, 2019; Chen et al, 2020; Goldberg et al, 2020; Liu et al, 2019; Ramos et al, 2020; Ross et al, 2019; K. Wang et al, 2020). However, the kinematic details of the foreshock rupture remain controversial, as some studies suggest the foreshock involved two orthogonal segments (Liu et al, 2019; Ross et al, 2019; Yang et al, 2020), while others prefer that the foreshock only ruptured the NE‐SW fault branch(es) (Barnhart et al, 2019; Goldberg et al, 2020).…”

Repeating Nontectonic Seasonal Stress Changes and a Possible Triggering Mechanism of the 2019 Ridgecrest Earthquake Sequence in California

“…We do not consider dynamic or static stress changes during or following the M w 6.4 and the M w 7.1 events, although the magnitude of such stress changes must be orders of magnitude higher than the preseismic seasonal stress changes we present in this manuscript (e.g., Barnhart et al., 2019; Chen et al., 2020; Goldberg et al., 2020; Jin & Fialko, 2020; Lozos & Harris, 2020; Magen et al., 2020; Mancini et al., 2020; Qiu et al., 2020; Ramos et al., 2020; Toda & Stein, 2020; Wang et al., 2020). Our interest is rather to quantify and characterize preseismic nontectonic stress changes, which we argue in this manuscript may have provided preseismic stress increases on right‐lateral faults within the area of rupture.…”

Cyclic Fault Slip Under the Magnifier: Co‐ and Postseismic Response of the Pamir Front to the 2015 Mw7.2 Sarez, Central Pamir, Earthquake

“…Co‐seismic activation of neighboring faults has already been reported using InSAR data (e.g., Fialko et al., 2002; Elliott et al., 2016; Wright et al., 2001). A particularly impressive example is the complex fracture pattern caused by the 2019 M w 7.1 Ridgecrest earthquake that induced slip and creep on the conjugate Garlock fault as observed by radar interferograms (Ramos et al., 2020; Xu et al., 2020). Both GPS and InSAR data testimony that the Pamir thrust system was co‐seismically activated and exhibits retrograde mm‐slip along tens of km.…”