High-resolution mapping of two large-scale transpressional fault zones in the California Continental Borderland: Santa Cruz-Catalina Ridge and Ferrelo faults
New mapping of two active transpressional fault zones in the California Continental Borderland, the Santa Cruz-Catalina Ridge fault and the Ferrelo fault, was carried out to characterize their geometries, using over 4500 line-km of new multibeam bathymetry data collected in 2010 combined with existing data. Faults identified from seafloor morphology were verified in the subsurface using existing seismic reflection data including single-channel and multichannel seismic profiles compiled over the past three decades. The two fault systems are parallel and are capable of large lateral offsets and reverse slip during earthquakes. The geometry of the fault systems shows evidence of multiple segments that could experience throughgoing rupture over distances exceeding 100 km. Published earthquake hypocenters from regional seismicity studies further define the lateral and depth extent of the historic fault ruptures. Historical and recent focal mechanisms obtained from first-motion and moment tensor studies confirm regional strain partitioning dominated by right slip on major throughgoing faults with reverse-oblique mechanisms on adjacent structures. Transpression on west and northwest trending structures persists as far as 270 km south of the Transverse Ranges; extension persists in the southern Borderland. A logjam model describes the tectonic evolution of crustal blocks bounded by strike-slip and reverse faults which are restrained from northwest displacement by the Transverse Ranges and the southern San Andreas fault big bend. Because of their potential for dip-slip rupture, the faults may also be capable of generating local tsunamis that would impact Southern California coastlines, including populated regions in the Channel Islands.
© 2015 American Geophysical Union. Received 29 August 2014; accepted 21 April 2015; accepted article online 24 April 2015; published online 30 May 2015. Exploration industry deep penetration seismic profiles released by WesternGeco for research purposes are available in the USGS NAMSS  database. U.S. Geological Survey multibeamsurveys are available in the NAMSS  database and Infobank . The USGS and WesternGeco do not warrant the use of these data nor make any claims or guarantees as to the accuracy of the data identification, acquisition parameters, processing methods, navigation, or database entries. The 2010 ALBACORE R/V Melville cruise multibeambathymetry data will be made available from the NOAA National Geophysical Data Center archive. The raster images of multibeam bathymetry used for this study will be available from the Southern California Earthquake Data Center with file descriptions provided in Table S1 in the supporting information. Chris Goldfinger provided important high-resolution seismic reflection data and several important multibeam bathymetry swaths from prior surveys. Joann Stock provided important multibeam swaths along the southern Ferrelo fault zone that filled important data gaps. Earthquake location parameters for events with focal mechanisms shown in this paper are presented in Table S2 in the supporting information. Seismicity data are available from the Southern California Earthquake Data Center (www.scedc.caltech.edu/eqcatalogs/) and from Astiz and Shearer . This work was supported by the National Science Foundation grants OCE-0825254 (MDK) and OCE-0824982 (DSW) and the Southern California Earthquake Center (grants 09094, 11100 and 13091, MRL). SCEC is funded by NSF Cooperative Agreement EAR-1033462 and USGS Cooperative Agreement G12AC20038. The SCEC contribution number for this paper is 1742. We are especially grateful to Alexander Densmore, Paul Umhoefer, Luciana Astiz, Kristin Rohr, and an anonymous reviewer for their thoughtful reviews of themanuscript that helped us to describe more coherently this complex area of active deformation. We thank Chris Sorlien for comments on early drafts of the manuscript and for numerous discussions of Borderland tectonics. Marc Kamerling shared many ideas regarding the Borderland tectonic evolution that helped provide the background for this research. Mike Barth insured that the high-resolution multichannel seismic data were of the highest quality during acquisition. Jason Chaytor's dissertation mapping was an important basis for understanding the subbottom geological structure and its correlation to seafloor morphology. The assistance of the Scripps Geological Data Center in coordinating outbound/inbound cruises to cover new Borderland territory with multibeam swaths during the past three decades is greatly appreciated. Kohler and Weeraratne are grateful to Captain Christopher Curl and the entire crew of R/V Melville for their assistance and flexibility in accommodating the additional multibeam bathymetry data gathering routes during the 2010 ALBACORE cruise.
Published - jgrf20393.pdf
Supplemental Material - jgrf20393-sup-0001-Supplementary.docx
Supplemental Material - jgrf20393-sup-0002-FigureS3.pdf