Segmentation Along the Newport-Inglewood Rose Canyon Fault Zone: Implications for Rupture Propagation

Abstract:

The Newport-Inglewood/Rose Canyon fault zone (NIRC) is an active component of the southern California strike-slip fault system in the Pacific-North American plate boundary. Despite its close proximity to densely populated coastal regions of Southern California, the NIRC fault geometry and expected earthquake behavior are poorly constrained. As a result of these uncertainties, current hazard models lack critical information regarding potential earthquake magnitudes and ground shaking caused by rupture on the offshore portion of the fault.

Here, we present an improved characterization of the NIRC fault zone’s architecture and segmentation. We employ nested marine seismic reflection data of varying vertical resolutions to map the NIRC location, strike, dip, and stepovers based on subsurface observations. These reflection data were collected in 1979, 2006, 2008, 2009 and 2013. We identify four main geometrical fault segments separated along strike by three stepovers between 0.5 and 3 km in width, whereby width is measured as the horizontal distance between fault strands or termini. Empirical studies of rupture propagation show that past earthquake ruptures in other regions have propagated across discontinuities of this width. We additionally employ a quantitative approach to constrain the potential earthquake magnitude for the NIRC fault zone by modeling the coulomb stress changes that result from possible rupture initiation scenarios. Earthquakes initiated on the central fault strand by Carlsbad Canyon favor through-going rupture across the entire length of the NIRC fault zone. Additionally, the modeling results suggest that the southernmost stepover by La Jolla may act as an inhibitor to through-going rupture due to the strike and dip of the adjacent fault despite the stepover’s short width. Finally, our stress modeling results suggest that the maximum potential magnitude of an earthquake rupturing all of the mapped offshore segments of the NIRC fault zone is Mw 7.5.