Los Padres National Forest (LPNF) occupies portions of the Coast and Transverse Ranges between Monterey and Gorman, California. High potential exists for the discovery of commercial quantities of oil and gas around the forest perimeter, much lower potential for such discoveries exists throughout most of the rest of the forest. LPNF is comprised principally of lower Tertiary and older sedimentary rocks with crystalline basement exposed as its northern and eastern ends. The forest overlaps major oil producing basins containing thick sequences of upper Tertiary sediments. Forest terrane south of Santa Ynez fault exhibits an east-west structural grain. Most of the remainder of LPNF exhibits a pronounced northwest-southwest structural grain. Folds range from vertical and overturned structures to broad, upright features that commonly persist for miles. Approximately 195 exploratory wells have been drilled within LPNF. Most of the reported shows occurred in Neogene strata of the surrounding basins. In Ventura Basin, shows were also reported from Paleogene rocks. Sespe and South Cuyama oil fields produced 769,000 equivalent bbl of oil from LPNF leases during 1992. Within LPNF, the potential for discovering commercial quantities of oil or gas in Cretaceous strata is very low. Paleogene strata offer low potential for such discoveriesmore » throughout most of the forest, but high potential near Sespe oil field. Potential from Neogene strata is moderate in the interior portion of the forest, but high where Miocene reservoirs are trapped beneath older strata around its perimeter. Of the nine high potential areas outlined in this study, South Cuyam, San Cayetano, and Sespe areas clearly have the greatest potential for the discovery of significant quantities of hydrocarbons.« less
In southern California, high rates of measured geodetic shortening occur where active basin-bounding faults thrust early-Cenozoic rocks over young uncon- solidated sediments. This implies that compaction, subsidence, and other nonelastic processes of footwall deformation may play an important role in contributing to the high rates of observed crustal strain. Even in the absence of active tectonic short- ening, sediment compaction alone can produce surficial motions that mimic deep fault slip or elastic strain accumulation. Differential compaction and subsidence of footwall sediments relative to hanging-wall rocks can lead to increased vertical sep- aration, basinward collapse, and fault rotation about horizontal axes. Such effects contribute to net horizontal and vertical motions in both geologic and geodetic data, and—if not properly accounted for—result in incorrect estimates of the inferred seismic hazard. Subsidence and compaction also increase the potential for gravity sliding toward the basin and the development of significant nonplanar 3D fault geometry. A prime example occurs along the San Cayetano fault that bounds the eastern Ventura basin. At shallow levels, a large thrust sheet (the Modelo Lobe) with low dip extends out in front of the more steeply dipping, planar fault segment by over 4 km, is nearly 2 km thick, and occupies over 60 cubic km. This geometry is strongly indicative of gravity-driven failure resulting from hanging-wall uplift, basinward tilt, and collapse, enhanced by footwall subsidence and compaction. Failure of this mega-slide off the hanging-wall block most likely occurred within the Rincon Formation, a thick ductile shale sequence that often accommodates detachment slip. This 3D geometry has significant implications for how the fault may behave during dynamic rupture and implies that additional care should be taken in extrapolating near-surface measure- ments or estimates of fault slip and dip to seismogenic depths.
A rigid element method of restoration (UNFOLD) is used to restore competent folded and faulted layers of the Ventura and Los Angeles basins to their initial horizontal state. Comparison of initial (undeformed) state with present (deformed state) allows one to estimate both the finite crustal deformation and its associated horizontal displacement field (relative to an arbitrary fixed line). Including data from the Santa Barbara Channel basin, the total finite displacement field for the western Transverse Ranges and vicinity (within the Pacific plate) is inferred from this map restoration and is modeled as a double fan closure. This model implies a 10° clockwise rotation of the northern boundary of the western Transverse Ranges and a 5° counterclockwise rotation of its northeast boundary. Lateral variation of the deformation reveals the heterogeneity of the subsurface deformation. Most of the major thrusts appear to initiate as en echelon structures along the left‐lateral northern margin and the right‐lateral northeastern margin of the studied area. The resulting deformation and displacement values closely match those derived by other geological methods (section balancing techniques or fault slip measurements) and by geophysical methods (geodetic, paleomagnetic, and focal mechanism data). Map restoration thus is a method that can independently quantify both local and regional deformation including folds and faults. This method also reveals the zones where problems of compatibility appear with the available geological and geophysical data and thus where the next studies might be focused.
Research Article| July 01, 2000 Map restoration of folded and faulted late Cenozoic strata across the Oak Ridge fault, onshore and offshore Ventura basin, California Christopher C. Sorlien; Christopher C. Sorlien 1Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar Jean-Pierre Gratier; Jean-Pierre Gratier 2Laboratory of Geophysics and Tectonophysics, IRIGM, B.P. 53, 38041 Grenoble, France Search for other works by this author on: GSW Google Scholar Bruce P. Luyendyk; Bruce P. Luyendyk 1Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar J. Scott Hornafius; J. Scott Hornafius 1Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar Thomas E. Hopps Thomas E. Hopps 3Rancho Energy Consultants, 250 South Hallock Drive, Suite 1, Santa Paula, California 93060, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Christopher C. Sorlien 1Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA Jean-Pierre Gratier 2Laboratory of Geophysics and Tectonophysics, IRIGM, B.P. 53, 38041 Grenoble, France Bruce P. Luyendyk 1Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA J. Scott Hornafius 1Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA Thomas E. Hopps 3Rancho Energy Consultants, 250 South Hallock Drive, Suite 1, Santa Paula, California 93060, USA Publisher: Geological Society of America Received: 12 Nov 1996 Revision Received: 01 Oct 1998 Accepted: 27 Jul 1999 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2000) 112 (7): 1080–1090. https://doi.org/10.1130/0016-7606(2000)112<1080:MROFAF>2.0.CO;2 Article history Received: 12 Nov 1996 Revision Received: 01 Oct 1998 Accepted: 27 Jul 1999 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Christopher C. Sorlien, Jean-Pierre Gratier, Bruce P. Luyendyk, J. Scott Hornafius, Thomas E. Hopps; Map restoration of folded and faulted late Cenozoic strata across the Oak Ridge fault, onshore and offshore Ventura basin, California. GSA Bulletin 2000;; 112 (7): 1080–1090. doi: https://doi.org/10.1130/0016-7606(2000)112<1080:MROFAF>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract 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 and its borders and to quantify their rate of deformation. Our study includes the onshore and offshore Ventura basin, the arcuate basin-bounding Oak Ridge reverse fault, and the Oxnard shelf to the south. Shortening, fault-slip, and crustal-block motions were studied using a three-dimensional map-restoration technique. Structure-contour maps on the 6 Ma surface and other horizons were digitized and restored to the initial horizontal state by unfolding them using the computer program UNFOLD and then fitting the unfolded surfaces across faults. Comparing the restored and present configuration allows us to estimate total net finite displacements relative to a fixed horizontal reference line.Average post–5 Ma shortening rates estimated from our restoration are slower than both post–1 Ma rates and present rates determined by global positioning 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 after 1 Ma. Displacement due to faulting and folding includes left-lateral strike-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 been previously interpreted as folds above thrust-fault ramps. This onshore-offshore block moves as one continuous thrust sheet. Similarly, beyond the well-studied onshore fault, a kinematically continuous offshore Oak Ridge–Mid-Channel left-oblique fault system is interpreted to continue at least an additional 100 km westward beneath the Santa Barbara Channel. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Research Article| July 01, 2000 Map restoration of folded and faulted late Cenozoic strata across the Oak Ridge fault, onshore and offshore Ventura basin, California Christopher C. Sorlien; Christopher C. Sorlien 1Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar Jean-Pierre Gratier; Jean-Pierre Gratier 2Laboratory of Geophysics and Tectonophysics, IRIGM, B.P. 53, 38041 Grenoble, France Search for other works by this author on: GSW Google Scholar Bruce P. Luyendyk; Bruce P. Luyendyk 1Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar J. Scott Hornafius; J. Scott Hornafius 1Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar Thomas E. Hopps Thomas E. Hopps 3Rancho Energy Consultants, 250 South Hallock Drive, Suite 1, Santa Paula, California 93060, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Christopher C. Sorlien 1Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA Jean-Pierre Gratier 2Laboratory of Geophysics and Tectonophysics, IRIGM, B.P. 53, 38041 Grenoble, France Bruce P. Luyendyk 1Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA J. Scott Hornafius 1Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA Thomas E. Hopps 3Rancho Energy Consultants, 250 South Hallock Drive, Suite 1, Santa Paula, California 93060, USA Publisher: Geological Society of America Received: 12 Nov 1996 Revision Received: 01 Oct 1998 Accepted: 27 Jul 1999 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2000) 112 (7): 1080–1090. https://doi.org/10.1130/0016-7606(2000)112<1080:MROFAF>2.0.CO;2 Article history Received: 12 Nov 1996 Revision Received: 01 Oct 1998 Accepted: 27 Jul 1999 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Christopher C. Sorlien, Jean-Pierre Gratier, Bruce P. Luyendyk, J. Scott Hornafius, Thomas E. Hopps; Map restoration of folded and faulted late Cenozoic strata across the Oak Ridge fault, onshore and offshore Ventura basin, California. GSA Bulletin 2000;; 112 (7): 1080–1090. doi: https://doi.org/10.1130/0016-7606(2000)112<1080:MROFAF>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract 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 and its borders and to quantify their rate of deformation. Our study includes the onshore and offshore Ventura basin, the arcuate basin-bounding Oak Ridge reverse fault, and the Oxnard shelf to the south. Shortening, fault-slip, and crustal-block motions were studied using a three-dimensional map-restoration technique. Structure-contour maps on the 6 Ma surface and other horizons were digitized and restored to the initial horizontal state by unfolding them using the computer program UNFOLD and then fitting the unfolded surfaces across faults. Comparing the restored and present configuration allows us to estimate total net finite displacements relative to a fixed horizontal reference line.Average post–5 Ma shortening rates estimated from our restoration are slower than both post–1 Ma rates and present rates determined by global positioning 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 after 1 Ma. Displacement due to faulting and folding includes left-lateral strike-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 been previously interpreted as folds above thrust-fault ramps. This onshore-offshore block moves as one continuous thrust sheet. Similarly, beyond the well-studied onshore fault, a kinematically continuous offshore Oak Ridge–Mid-Channel left-oblique fault system is interpreted to continue at least an additional 100 km westward beneath the Santa Barbara Channel. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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