The Palos Verdes Fault offshore Southern California: Late Pleistocene to present tectonic geomorphology, seascape evolution, and slip rate estimate based on AUV and ROV surveys

Abstract

The Palos Verdes Fault (PVF) is one of few active faults in Southern California that crosses the shoreline and can be studied using both terrestrial and subaqueous methodologies. To characterize the near‐seafloor fault morphology, tectonic influences on continental slope sedimentary processes and late Pleistocene to present slip rate, a grid of high‐resolution multibeam bathymetric data, and chirp subbottom profiles were acquired with an autonomous underwater vehicle (AUV) along the main trace of PVF in water depths between 250 and 600 m. Radiocarbon dates were obtained from vibracores collected using a remotely operated vehicle (ROV) and ship‐based gravity cores. The PVF is expressed as a well‐defined seafloor lineation marked by subtle along‐strike bends. Right‐stepping transtensional bends exert first‐order control on sediment flow dynamics and the spatial distribution of Holocene depocenters; deformed strata within a small pull‐apart basin record punctuated growth faulting associated with at least three Holocene surface ruptures. An upper (shallower) landslide scarp, a buried sedimentary mound, and a deeper scarp have been right‐laterally offset across the PVF by 55 ± 5, 52 ± 4 , and 39 ± 8 m, respectively. The ages of the upper scarp and buried mound are approximately 31 ka; the age of the deeper scarp is bracketed to 17–24 ka. These three piercing points bracket the late Pleistocene to present slip rate to 1.3–2.8 mm/yr and provide a best estimate of 1.6–1.9 mm/yr. The deformation observed along the PVF is characteristic of strike‐slip faulting and accounts for 20–30% of the total right‐lateral slip budget accommodated offshore Southern California.

Kinematic analysis of secondary faults within a distributed shear-zone reveals fault linkage and increased seismic hazard

“…Detailed structural mapping, as well as kinematic and seismogenic characterization of 41 active submarine fault systems, is essential for determining possible fault linkages for potential 42 rupture scenarios and, consequently, for improving the assessment of the seismic and tsunami 43 hazard in densely populated coastal areas. Recent advances in seafloor and subsurface imaging 44 have made it possible to obtain high-resolution seismic and bathymetric data, which can be used to accurately characterize the kinematic patterns and tectonic architecture of submarine faults with unprecedented detail (Armijo et al, 2005;Barnes, 2009;Bartolome et al, 2012;Brothers et al, 2015;Escartín et al, 2016;Gasperini et al, 2011a,b;Gràcia et al, 2012Gràcia et al, , 2006Martínez-Loriente et al, 2013;McNeill et al, 2007;McNeill and Henstock, 2014;Moreno et al, 2016;Perea et al, 2012;Polonia et al, 2012;Sahakian et al, 2017). In addition, methods have been developed to determine the seismogenic potential and earthquake history of single faults based on on-fault marine paleoseismology (e.g.…”

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

“…Based on the 9 samples that acquired ages for both benthic and planktonic foraminifera, we calculated an average difference in reservoir age of 900 years. For this difference in reservoir age, benthic foraminifera < 12,000 year would have a reservoir age of 1700 year, which is comparable to the reservoir age of 1750 for benthic foraminifera used by Mix et al (1999), , Brothers et al (2015), and others. Thus, we used this value of 1750 years for a benthic reservoir age.…”

“…Channel gradient exerts controls on turbidity flow behavior, as the velocity of turbidity flows is proportional to gradient (McHargue et al, 2011). Steep gradients along broader scales are often related to greater incision, whereas gentler gradients are related to deposition (Prather, 2000;McHargue et al, 2011;Brothers et al, 2015;Maier et al, 2017). Breaks in channel gradient can emplace turbidites and steep gradients can cause bypass of turbidity currents; as a result, gradient can influence the frequency and timing of turbidite emplacement.…”

Earthquake crisis unveils the growth of an incipient continental fault system

“…3a-c) using multibeam sonars mounted on two AUVs (see Methods). Multi-scale acoustic mapping techniques, such as swath-bathymetry allow identifying the geomorphological expression of active faults, such as seafloor ruptures, fault scarps and fault traces 27,28 . The AUV bathymetric data clearly highlight the surface expression of the AIFS, whose N.B.…”