A numerical study of strike‐slip bend formation with application to the Salton Sea pull‐apart basin

Abstract

How stepovers of strike‐slip faults connect to form bends is a question important for understanding the formation of push‐up ranges (restraining bends) and pull‐apart basins (releasing bends). We investigated the basic mechanics of this process in a simple three‐dimensional viscoelastoplastic finite element model. Our model predicts localized plastic strain within stepovers that may eventually lead to the formation of strike‐slip bends. Major parameters controlling strain localization include the relative fault strength, geometry of the fault system, and the plasticity model assumed. Using the Drucker‐Prager plasticity model, in which the plastic yield strength of the crust depends on both shear and normal stresses, our results show that a releasing bend is easier to develop than a restraining bend under similar conditions. These results may help explain the formation of the Salton Sea pull‐apart basin in Southern California 0.5–0.1 Ma ago, when the stepover between the Imperial Fault and the San Andreas Fault was connected by the Brawley seismic zone.

Recency of Faulting and Subsurface Architecture of the San Diego Bay Pull-Apart Basin, California, USA

“…(1) Analog models involving laboratory experiments using clay and sand as proxies to crustal materials (Dooley and McClay, 1997;Rahe et al, 1998;Wu et al, 2009), (2) kinematic models based on static stress and strain conditions, plate motion boundary conditions, and assumed material properties (Sanderson and Marchini, 1984;Fossen and Tikoff, 1993;Tikoff and Teyssier, 1994;Teyssier et al, 1995), and (3) numerical models grounded in continuum mechanics and conservation laws focused on temporal changes in a system by use of finite element simulations (Rogers, 1980;Gölke et al, 1994;Ye et al, 2015;van Wijk et al, 2017). With conventional pull-apart basin models unable to explain the various strike and dip orientations of the Group-1, Group-2, and La Nacion faults, we provide a new structural interpretation for the San Diego Bay pull-apart basin and compare it to results from these three types of models.…”

“…These structures receive considerable attention in academic studies not only due to their abundance, but also their high potential in resource extraction, and their role in earthquake rupture processes (e.g., Mann et al, 1983;Oglesby, 2005;Mann, 2007;Wesnousky, 2008;Brothers et al, 2009;Wu et al, 2009;Watt et al, 2016;van Wijk et al, 2017). A significant amount of previous work has focused on the evolution of pullapart basins, from early-stage spindle-shaped basins through the extreme case of significant lithospheric thinning and the development of a spreading ridge (Mann et al, 1983;Lonsdale, 1995;Mann, 2007;Wu et al, 2009;Dooley and Schreurs, 2012;Ye et al, 2015;van Wijk et al, 2017).…”

“…Through field observation (e.g., Garfunkel and Ben-Avraham, 1996;Mann, 2007;Wesnousky, 2008;Brothers et al, 2009;Watt et al, 2016), analogue models (e.g., Wu et al, 2009;Dooley and Schreurs, 2012), and numerical studies (e.g., Oglesby, 2005;Ye et al, 2015;van Wijk et al, 2017), a basic understanding of pullapart basins has emerged that focuses on fault structure and stratigraphic character of the central region of subsidence that develops in the space between the two principal displacement zones (i.e., the main strike-slip fault sections). The predictive models produced by such studies investigate strike-slip fault step-overs and oblique deformation at a range of different scales and boundary conditions.…”

“…Kinematic models using plate boundary conditions and fault geometry (but not explicitly considering stress conditions), provide a broad scale perspective on deformation characteristics and strain partitioning (e.g., Tikoff and Teyssier, 1994;Teyssier et al, 1995). Predictions of smaller scale (intra-basin) faulting and deformation through time is provided by analogue and numerical models that simulate lithospheric conditions with either proxy material (e.g., sand and clay) (e.g., Dooley and Schreurs, 2012), or simplified fault geometries and stress conditions (e.g., Ye et al, 2015). While valuable as a framework for field observations, these models may have scaling limitations, or may be over simplified due to real-world crustal heterogeneities.…”

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

“…An important feature of this code is the inclusion of plastic strain: it uses steady state plastic creep on the fault zones to simulate longterm fault slip, and it allows plastic strain to occur in the crust outside the fault zones when the plastic yield is reached. In places of highly localized plastic strain, initiation of new faults (or reactivation of preexisting faults) may be expected [Li and Liu, 2007;Li et al, 2009;Liu et al, 2010;Ye et al, 2015]. Detailed description of this code is given by Li et al [2009]; here we briefly describe the model setup for this study (Figure 2).…”