The Newport‐Inglewood/Rose Canyon (NIRC) fault zone is an active strike‐slip fault system within the Pacific‐North American plate boundary in Southern California, located in close proximity to populated regions of San Diego, Orange, and Los Angeles counties. Prior to this study, the NIRC fault zone's continuity and geometry were not well constrained. Nested marine seismic reflection data with different vertical resolutions are employed to characterize the offshore fault architecture. Four main fault strands are identified offshore, separated by three main stepovers along strike, all of which are 2 km or less in width. Empirical studies of historical ruptures worldwide show that earthquakes have ruptured through stepovers with this offset. Models of Coulomb stress change along the fault zone are presented to examine the potential extent of future earthquake ruptures on the fault zone, which appear to be dependent on the location of rupture initiation and fault geometry at the stepovers. These modeling results show that the southernmost stepover between the La Jolla and Torrey Pines fault strands may act as an inhibitor to throughgoing rupture due to the stepover width and change in fault geometry across the stepover; however, these results still suggest that rupture along the entire fault zone is possible.
Maps showing Quaternary deposits and active fault traces, paleoseismic trenches, scarp diffusion analyses, and soil characteristics in displaced alluvial surfaces are combined with previous paleoseismic studies to examine the character of late Pleistocene earthquake recurrence and estimate the net extension rate across the interior of the Great Basin of the western United States at the latitude of ~39°N. The study area includes faults bounding the Desatoya, Toiyabe, Moni tor, Simpson Park, Toquima, Antelope, Fish Creek, Butte, Egan, and Schell Creek Ranges. The rate of earthquake recurrence is documented to be signifi cantly less than observed within the Walker Lane-Central Nevada seismic belt and along the Wasatch, which respectively defi ne the western and eastern bound aries of the interior of the Great Basin. Late Pleistocene extension across the interior of the Great Basin is calculated to equal ~1 mm/yr across the 450 km transect and is consistent with rates defi ned by recent geodetic studies. The agreement in extension rate estimates over different time scales indicates that tectonic deformation in the Great Basin has been characterized by relatively slow and consistent extension through the late Pleistocene to the present. The internal deformation of the Great Basin and the pattern of strain release may refl ect a broad transition zone from northwest-directed shear in the west to extension along the eastern edge of the Pacifi c-North American plate boundary. Downloaded from System's catalog (http://quake.geo.berkeley.edu/anss/catalog-search.html). Faults are from Dohernwend et al. (1996) and the Fault and Fold Database of the U.S. Geological Survey (Haller et al., 2004: http://qfaults.cr.usgs.gov). Plate motion velocity vector is from DeMets and Dixon (1999). Approximate boundaries of provinces within the Great Basin were taken from Bennett et al. (2003). (B) Location of normal fault-bounded mountain ranges within the Great Basin that are the focus of this study. Also indicated are mountain ranges referred to in the text. Faults were taken from the Fault and Fold Database of the U.S. Geological Survey (Haller et al., 2004: http://qfaults.cr.usgs.gov). White stars are permanent global positioning system (GPS) monuments recently installed as part of the EarthScope element of the Plate Boundary Observatory project. Black arrows are crustal velocity vectors modifi ed from Hammond and Thatcher (2004). U.S. Highway 50 and Highway 6 are shown in black. EF-East Gate fault; CA-Clan Alpine Range; DES-Desatoya Range; TOI-Toiyabe Range; TOQ-Toquima Range; SP-Simpson Park Mountains; M-Monitor Range; A-Antelope Range; FC-Fish Creek Range; D-Diamond Range; P-Pancake Range; WP-White Pine Range; G-Grant Range; B-Butte Range; E-Egan Range; SE-South Egan Range; SC-Schell Creek Range; S-Snake Range.
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