How fault evolution changes strain partitioning and fault slip rates in Southern California: Results from geodynamic modeling

Abstract

In Southern California, the Pacific‐North America relative plate motion is accommodated by the complex southern San Andreas Fault system that includes many young faults (<2 Ma). The initiation of these young faults and their impact on strain partitioning and fault slip rates are important for understanding the evolution of this plate boundary zone and assessing earthquake hazard in Southern California. Using a three‐dimensional viscoelastoplastic finite element model, we have investigated how this plate boundary fault system has evolved to accommodate the relative plate motion in Southern California. Our results show that when the plate boundary faults are not optimally configured to accommodate the relative plate motion, strain is localized in places where new faults would initiate to improve the mechanical efficiency of the fault system. In particular, the Eastern California Shear Zone, the San Jacinto Fault, the Elsinore Fault, and the offshore dextral faults all developed in places of highly localized strain. These younger faults compensate for the reduced fault slip on the San Andreas Fault proper because of the Big Bend, a major restraining bend. The evolution of the fault system changes the apportionment of fault slip rates over time, which may explain some of the slip rate discrepancy between geological and geodetic measurements in Southern California. For the present fault configuration, our model predicts localized strain in western Transverse Ranges and along the dextral faults across the Mojave Desert, where numerous damaging earthquakes occurred in recent years.

Kinematics and Evolution of the Southern Eastern California Shear Zone, Based on Analysis of Fault Strike, Distribution, Activity, Roughness, and Secondary Deformation

“…The shear zone connects to the Walker Lane belt and exists due to the strain imposed by rifting in the Gulf of California on the south and motion of the Sierra Nevada microplate away from the extending Basin and Range in the north, as well as due to the mechanical anisotropy of the lithosphere associated with Miocene Basin and Range extension (Li & Liu, 2006; M. Liu et al., 2010; Plattner et al., 2010). The inability of the misaligned southern SAF (i.e., “big bend”) to accommodate plate motion results in the ECSZ as well as other regional structures, including the Transverse Ranges and San Jacinto fault (Dixon & Xie, 2018; Dokka et al., 1998; Thatcher et al., 2016; Ye & Liu, 2017).…”

“…This zone can be divided into several domains of distinct deformation style that have accommodated a total of ∼50–75 km of dextral slip over the past ∼6–10 Ma (Andrew & Walker, 2016; Dokka & Travis, 1990a, 1990b; Glazner et al., 2002; Jachens et al., 2002; Lease et al., 2009; Singleton & Gans, 2008). Although activity is thought to have been diachronous and evolved with changes in regional strain partitioning (e.g., onset of the San Jacinto fault at 1–2 Ma), the timing of onset of individual faults and overall spatiotemporal evolution of the ECSZ are not well constrained (Andrew & Walker, 2016; Glazner et al., 2002; M. Liu et al., 2010; D. M. Miller & Yount, 2002; M. M. Miller et al., 2001; Oskin & Iriondo, 2004; Oskin et al., 2007; Ye & Liu, 2017).…”

“…Liu et al, 2010;Plattner et al, 2010). The inability of the misaligned southern SAF (i.e., "big bend") to accommodate plate motion results in the ECSZ as well as other regional structures, including the Transverse Ranges and San Jacinto fault (Dixon & Xie, 2018;Dokka et al, 1998;Thatcher et al, 2016;Ye & Liu, 2017).…”

“…Liu et al, 2010;D. M. Miller & Yount, 2002; M. M. Miller et al, 2001;Oskin & Iriondo, 2004;Oskin et al, 2007;Ye & Liu, 2017).…”

The role of the Polochic Fault as part of the North American and Caribbean Plate boundary: Insights from the infill of the Lake Izabal Basin

“…Although the Polochic Fault is contemporarily considered a minor fault of the plate boundary (Authemayou et al, 2012;Franco et al, 2012), it still bears the risk of producing recurring M W 6-7 earthquakes (Brocard, Anselmetti, & Teyssier, 2016). This is, to some degree, analogous to the strike-slip system of the Eastern California Shear Zone, where strain is transferred north from the San Andreas Fault (Ye & Liu, 2017), and where the majority of recent, large earthquakes have localized (Fialko, Simons, & Agnew, 2001;Haukksson, Jones, Hutton, & Eberhart-Phillips, 1993;Ross et al, 2019). indicating that the Polochic Fault was the only fault of the plate boundary between 15 and 10 Ma (Scenario 1) or between 12 and 7 Ma (Scenario 4).…”