Three‐Dimensional Structure, Ground Rupture Hazards, and Static Stress Models for Complex Nonplanar Thrust Faults in the Ventura Basin, Southern California

Abstract

To investigate the subsurface geometry of a recently discovered, seismically active fault in the Ventura basin, southern California, USA, we present a series of cross sections and a new three-dimensional fault model across the Southern San Cayetano fault (SSCF) based on integration of surface data with petroleum industry well log data. Additionally, the fault model for the SSCF, along with models of other regional faults extracted from the Southern California Earthquake Center three-dimensional Community Fault Model, are incorporated in static Coulomb stress modeling to investigate static Coulomb stress transfer between thrust faults with complex geometry and to further our understanding of stress transfer in the Ventura basin. The results of the subsurface well investigation provide evidence for a low-angle SSCF that dips~15°north and connects with the western section of the San Cayetano fault around 1.5-3.5 km depth. We interpret the results of static Coulomb stress models to partly explain contrasting geomorphic expression between different sections of the San Cayetano fault and a potential mismatch in timings between large-magnitude uplift events suggested by paleoseismic studies on the Pitas Point, Ventura, and San Cayetano faults. In addition to new insights into the structure and potential rupture hazard of a recently discovered active reverse fault in a highly populated area of southern California, this study provides a simple method to model static Coulomb stress transfer on complex geometry faults in fold and thrust belts.

Diachronous Quaternary Development of the Jiayuguan Fault and Implications for Strain Compartmentalization and Modern Earthquake Hazards in the NW Hexi Corridor, China

“…The 2008 Mw 7.9 Wenchuan earthquake in eastern Tibet provides a good example of a multi‐fault rupture event on strike‐parallel thrust faults that merge at depth (e.g., P. Zhang et al., 2010). Conducting additional geophysical surveys to evaluate the deep structural connectivity of major faults in the JYGF region coupled with additional palaeo‐seismological studies will be required to further document the potential seismic hazard to population centers and infrastructure in the NW Hexi Corridor (cf., Hughes et al., 2020).…”

“…The projected low-angle dip of the JYGF from our kinematic model (Figure 9) suggests that the JYGF could deeply connect with the Yinwashan and Xinminpu faults, forming an imbricate thrust or obliqueslip dextral thrust fault system. This potential subsurface connectivity implies a high seismic hazard due to potentially complex fault interactions and static Coulomb stress transfer (e.g., Hughes et al, 2018Hughes et al, , 2020Stahl et al, 2016). The 2008 Mw 7.9 Wenchuan earthquake in eastern Tibet provides a good example of a multi-fault rupture event on strike-parallel thrust faults that merge at depth (e.g., P. Zhang et al, 2010).…”

Fault slip-rates and Coulomb stress interactions in the intersection zone of the Hope, Kelly and Alpine Faults, South Island, New Zealand

“…Rectangular discretization of a fault surface is used to create variable fault geometry, based on surface observations, to model the CFS resulting from representative earthquakes in the fault system. The main faults in the Alpine-Kelly-Hope Fault network have been discretised with variations in strike, dip and rake, following the approaches of Mildon et al (2016) and Hughes et al (2020). We conducted CFS modelling using Coulomb 3.4 (Toda et al, 2005).…”

Paleoseismological Findings at a New Trench Indicate the 1714 M8.1 Earthquake Ruptured the Main Frontal Thrust Over all the Bhutan Himalaya

“…Coulomb stress transfer (CST) changes the state of stress around the rupture fault, with some areas (or receiver faults) experiencing an increase in Coulomb stress and others experiencing a decrease in stress (Lin and Stein, 2004). Typically, changes in stress along or across strike are investigated for planar faults, however the MHT has a ramp-flat geometry, thus CST modeling for non-planar faults (Stahl et al, 2016;Hughes et al, 2020) is better suited. Therefore, we use CST to try and determine the potential interaction and triggering between deep ramp earthquakes and the shallow ramp and flat portion of the MHT.…”

“…We performed calculations of coseismic stress changes using a realistic ramp-flat geometry of the MHT and the strike-variable surface trace of the MFT. The method used to generate strikevariable fault planes from surface fault traces was developed by Mildon et al (2016) and dip-variable fault planes in Hughes et al (2020). The MHT was modeled as a series of 20-km rectangular elements comprising the non-planar fault surface.…”