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

Abstract

<jats:title>ABSTRACT</jats:title> <jats:p>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 Mw 7.1 mainshock. But the central Garlock fault, despite being located immediately south of this sequence, did not coseismically fail. Instead, the Garlock fault underwent postseismic 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 (ΔCFS), and dynamic rupture modeling. We show that positive ΔCFSs 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 the 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.</jats:p>

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).…”

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.…”

Effect of Asymmetric Topography on Rupture Propagation Along Fault Stepovers

“…However, I have to point out that the current models don't take into account factors such as depth dependent stresses (Aochi & Tsuda, 2023), stress heterogeneity (Douilly et al., 2020; Duan & Oglesby, 2007; Wang et al., 2020) and off‐fault plasticity (Gabriel et al., 2013) that could also affect the likelihood of throughgoing rupture. This is particularly important considering that the 2019 Ridgecrest caused an increase in stress on the Garlock fault segment near the segmentation (Ramos et al., 2020). In addition, Toda and Stein (2020) showed an increase in Coulomb stress change on the section of the Garlock fault closer to the San Andreas fault.…”

“…Also, the left-lateral Garlock fault system, which is composed of two segments separated by an extensional stepover width of 3-4 km, has high mountain ranges on its northern side and almost a flat topography on the southern side (Figure 1). This stepover is particularly important because the recent 2019 Ridgecrest 3 of 14 sequence triggered significant seismicity on the Garlock fault (Cochran et al, 2020;Shelly, 2020) and an important increase in shear stress was also observed on that segment near the segmentation (Ramos et al, 2020). Considering that the aforementioned stepover modeling studies assumed a flat topography and didn't explore whether surfaces with irregular topographies can also impact rupture propagation across fault segmentation, it is worth investigating whether topography can also affect rupture jump across fault stepovers.…”