Origin of the Palos Verdes Restraining Bend and Its Implications for the 3D Geometry of the Fault and Earthquake Hazards in Los Angeles, California

Abstract

ABSTRACT The Palos Verdes fault zone (PVFZ) extends across the southwestern Los Angeles basin and Inner Continental Borderland, California, and is considered capable of generating large (Mw>7), damaging earthquakes with short recurrence intervals. The 110 km long fault zone is composed of vertical and moderately dipping segments that accommodate oblique, right-lateral reverse displacement. Onshore, there is a counterclockwise reorientation in the PVFZ’s strike, which produces a major restraining bend that generates the Palos Verdes Peninsula. Here, we use well and seismic reflection data to develop kinematic models that show folding of the PVFZ by the Wilmington blind thrust led to formation of the restraining bend. North of the peninsula in Santa Monica Bay, debate persists over the extent, geometry, and activity of the PVFZ. Here, we analyze a dense grid of high-resolution seismic reflection data and present a new mapping of the Santa Monica Bay segment of the PVFZ, including multiple active splays (e.g., Redondo Canyon fault zone) that occur within a broad damage zone at the northern termination of the fault system. Based on these insights and prior studies, we develop a new, comprehensive 3D model of the PVFZ including its Santa Monica Bay, San Pedro Bay, and Lasuen Knoll segments. The sizes of these segments indicate that PVFZ is capable of larger events than previously reported—Mw 7.1–7.4 for single-segment ruptures and Mw 7.4–7.8 for multisegment ruptures. Based on a reported slip rate of 1.1–5.9 mm/yr, average recurrence intervals for these single- and multisegment rupture scenarios are 580–610 and 760–1170 yr, respectively.