Seismic constraints on the architecture of the Newport‐Inglewood/Rose Canyon fault: Implications for the length and magnitude of future earthquake ruptures

Abstract

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.

Strike-Slip Transpressional Uplift Offshore San Onofre, California Inhibits Sediment Delivery to the Deep Sea

“…The anticlinal feature is onlapped by younger sediment (Sahakian et al, 2017). Deformation offshore San Onofre is older than at other locations to the north or south on the NIRC fault (Sahakian et al, 2017), as the transgressive surface is not displaced (Klotsko et al, 2015). It is estimated that fault activity pre-dates 100 ka (Sahakian et al, 2017).…”

“…The left lateral jog between these two segments engenders transpression and forms an anticlinal feature responsible for the widening of the shelf in this region (Sahakian et al, 2017). The anticlinal feature is onlapped by younger sediment (Sahakian et al, 2017). Deformation offshore San Onofre is older than at other locations to the north or south on the NIRC fault (Sahakian et al, 2017), as the transgressive surface is not displaced (Klotsko et al, 2015).…”

“…Where the shelf is wide, two segments of the NIRC fault are separated by a stepover of 1 km (Figure 1B). The left lateral jog between these two segments engenders transpression and forms an anticlinal feature responsible for the widening of the shelf in this region (Sahakian et al, 2017). The anticlinal feature is onlapped by younger sediment (Sahakian et al, 2017).…”

“…(B) Previously mapped active faults within the study area are shown. Blue faults are from Sahakian et al (2017) and purple faults are from Conrad et al (2018). FZ = Fault Zone.…”

“…Sediment dispersal in the study area is affected most by the active Newport-Inglewood Fault, which is part of the Newport-Inglewood/Rose-Canyon (NIRC) Fault (Figure 1B; Klotsko et al, 2015;Sahakian et al, 2017). The right-lateral strike-slip NIRC Fault trends northwest-southeast, has been active since at least the Miocene in the north, and it is estimated to accommodate 0.5-2 mm a −1 of Pacific-North American plate boundary motion (Freeman et al, 1992).…”