Map restoration of folded and faulted late Cenozoic strata across the Oak Ridge fault, onshore and offshore Ventura basin, California

The Ventura basin lies within the east-west-trending active fold-and-thrust belt of the western Transverse Ranges, California, This basin has been the site of significant earthquakes on structures within it and bordering it. The purpose of our study is to identify the main structures in the basin an d its borders and to quantify their rate of deformation, Our study includes the onshore and offshore Ventura basin, the arcuate basin-bounding Oak Rid ge reverse fault, and the Oxnard shelf to the south. Shortening, fault-slip , and crustal-block motions were studied using a three-dimensional map-rest oration technique. Structure-contour maps on the 6 hla surface and other ho rizons were digitized and restored to the initial horizontal state by unfol ding them using the computer program UNFOLD and then fitting the unfolded s urfaces across faults, Comparing the restored and present configuration all ows us to estimate total net finite displacements relative to a tied horizo ntal reference line, Average post-5 Ma shortening rates estimated front our restoration are slow er than both post-1 Ma rates and present rates determined by global positio ning systems. Most shortening due to folding in the onshore basin is post-1 Ma, although slip on the Oak Ridge Fault has occurred both before and afte r 1 Ma, Displacement due to faulting and folding includes left-lateral stri ke-slip motion on the northeast-southwest coastal segment of the Oak Ridge fault and associated clockwise rotation of the adjacent Ventura basin, The Oxnard shelf is bordered to the south by mountains and islands that have be en previously interpreted as folds above thrust-fault ramps. This onshore-o ffshore block moves as one continuous thrust sheet. Similarly, beyond the w ell-studied onshore fault, a kinematically continuous offshore Oak Ridge-Mi d-Channel left-oblique fault system is interpreted to continue at least an additional 100 km westward beneath the Santa Barbara Channel.