Abstract
The Ventura Thrust system in California is capable of producing large magnitude earthquakes. Geological studies suggest that the fault geometry is complex, composed of multiple segments at different dips: thrust ramps dipping 30°–50° linked with bed-parallel décollements dipping < 10°. These latter types of gently dipping faults form due to preexisting weaknesses in the crust, and therefore have different frictional parameters from thrust ramps; the faults also experience different stresses because of how stresses are resolved onto the fault planes. Here, we use a two-dimensional fault model to assess how geometry and frictional properties of the ramp/décollement system should affect the seismic cycle. We test velocity-strengthening, velocity-weakening, and conditionally stable décollements, and in addition explore how the dip angle of the décollement changes the earthquake behavior. A velocity-strengthening décollement cannot replicate the through-going earthquake ruptures that have been inferred for the Ventura fault system. We therefore suggest that this and other décollements may be better represented using a velocity-weakening or conditionally stable response. Our results show that minor variations in fault geometry produce slip amounts and recurrence intervals that differ only by 10–20%, but do not fundamentally alter the types of earthquakes and interseismic slip. We conclude that geological constraints on fault geometry are typically sufficient to produce modeled earthquake sequences that are statistically consistent with paleoseismic records. However, both frictional parameters along the fault and effective normal stress influence earthquake rupture patterns significantly. More research is needed to adequately constrain these quantities in order for earthquake rupture models to work as effective predictors of fault behavior.
Highlights
Continental thrust fault systems are capable of producing large magnitude earthquakes, often near large population centers (e.g., 2008 Mw = 7.9 Wenchuan earthquake, China; 2015 Mw = 7.8 Gorkha earthquake, Nepal)
We adopt a two-dimensional model of the Ventura Thrust system to assess the sensitivity of dynamic earthquake models to changes in geometry and frictional properties of a ramp/decollement system
By testing three frictional parameterizations for the decollement (Case 1—velocitystrengthening; Case 2—unstable velocity-weakening, and Case 3—conditionally stable velocity-weakening), we evaluate which frictional parameters produce a better representation of the paleoseismic record along this fault
Summary
The Western Transverse Ranges, 10–20 km northwest of the city of Los Angeles, is one such region In this area, multiple fault strands may rupture together in large events along the Ventura-Pitas Point fault system (Hubbard et al 2014; McAuliffe et al 2015; Rockwell et al 2016). Given the sparsity of the earthquake record and the long recurrence interval of large earthquakes, such forecasts may rely in part on dynamic rupture models, to assess how geometry affects rupture (e.g., Li and Liu 2016; Qiu et al 2016; Yu et al 2018). We evaluate the effect of smoothing fault intersections to replicate the curved fault geometry studied by Ryan et al (2015) to evaluate the sensitivity of the models to such geometric variations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
