High-Resolution 3D Seismic Imaging of Fault Interaction and Deformation Offshore San Onofre, California

James J Holmes,Neal W Driscoll,Graham M Kent

doi:10.3389/feart.2021.653672

Abstract

The Inner California Borderland (ICB) records a middle Oligocene transition from subduction to microplate capture along the southern California and Baja coast. The closest nearshore fault system, the Newport-Inglewood/Rose Canyon (NIRC) fault complex is a dextral strike-slip system that extends primarily offshore approximately 120 km from San Diego to Newport Beach, California. Holocene slip rates along the NIRC are 1.5–2.0 mm/year in the south and 0.5 mm/year along its northern extent based on trenching and well data. High-resolution 3D seismic surveys of the NIRC fault system offshore of San Onofre were acquired to define fault interaction across a prominent strike-slip step-over. The step-over deformation results in transpression that structurally controls the width of the continental shelf in this region. Shallow coring on the shelf yields a range of sedimentation rates from 0.27–0.28 mm/year. Additionally, a series of smaller anticlines and synclines record subtle changes in fault trends along with small step-overs and secondary splay faults. Finally, sedimentary units onlapping and dammed by the anticline, place constraints on the onset of deformation of this section of the NIRC fault system. Thickness estimates and radiocarbon dating yield ages of 560,000 to 575,000 years before present for the onset of deformation.

Highlights

Specialty section: This article was submitted to Structural Geology and Tectonics, a section of the journal Frontiers in Earth Science
A series of stair diagrams are presented to highlight the three-dimensional architecture of the Newport-Inglewood/Rose Canyon (NIRC) fault segments and attendant deformation (Figures 3–9, 11)
The images presented are bounded by an upper time-slice at 125 ms of two-way travel time (TWT) (∼96 m) and a lower time-slice at 350 ms TWT (∼279 m), with the cross-section point of view moving from north to south

Summary

Introduction

Specialty section: This article was submitted to Structural Geology and Tectonics, a section of the journal Frontiers in Earth Science. The Inner California Borderland (ICB) (Figure 1B) is a region marked by tectonic deformation offshore southern California and northern Baja that records a middle Oligocene transition from a subduction regime to microplate capture (Bohannon and Geist, 1998). Fault Deformation Offshore San Onofre to early Pliocene, the margin has been dominated by rightlateral strike-slip faulting, often on reactivated Mesozoic structures (Hill, 1971; Grant and Shearer, 2004) These faults account for approximately 10% of the total slip between the North America and Pacific plates (DeMets and Dixon, 1999; Platt and Becker, 2010)

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