Analysis of Fault-Fold Structures along the Newport-Inglewood Rose Canyon Fault System at an unprecedented scale using 3D P-Cable seismic reflection data

American Geophysical Union Fall Meeting, 10-14 December 2018, Washington D.C.[Poster] The Inner California Borderlands (ICB) is situated off the coast of southern California and northern Baja. The structural and geomorphic characteristics of the area record a middle Oligocene transition from subduction to microplate capture along the California coast. Marine stratigraphic evidence shows large-scale extension and rotation overprinted by modern strike slip deformation. Geodetic and geologic observations indicate that approximately 6-8 mm/yr of Pacific-North American relative plate motion is accommodated by offshore strike-slip faulting in the ICB. The farthest inshore 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 the San Joaquin Hills near Newport Beach, California. Based on trenching and well data, the NIRC fault system Holocene slip rate is 1.5-2.0 mm/yr to the south and 0.5-1.0 mm/yr along its northern extent. An earthquake rupturing the entire length of the system could produce an Mw 7.0 earthquake or larger. West of the main segments of the NIRC fault complex is the San Onofre Fault Trend (SOT), and San Mateo Fault Trend (SMT) along the continental slope. Previous work concluded that these are part of a strike-slip system that eventually merges with the NIRC complex. Others have interpreted these systems as deformation associated with the Oceanside Blind Thrust Fault (OBT) purported to underlie most of the region. In late 2013, we acquired the first high-resolution 3D P-Cable seismic surveys (3.125 m bin resolution) of the San Onofre Trend as part of the Southern California Regional Fault Mapping project aboard the R/V New Horizon. Analysis of this data volume provides important new insights and constraints on the fault segmentation and transfer of deformation. Based on the new 3D sparker seismic data, our preferred interpretation for the San Onofre fault trend is a set of transpressional features associated with a shear zone and right lateral fault strands splaying off the NIRC fault. Such a scenario also is consistent with observations from the 3D volume along the shelf and upper slope that images westward stepping faults splaying off the NIRC system.[Meeting] The Newport-Inglewood Rose Canyon (NIRC) Fault system is a complex dextral strike-slip system that is located primarily offshore for approximately 120 km from San Diego to the San Joaquin Hills near Newport Beach, California. Based on trenching and well data, the NIRC Fault Holocene slip rate is 1.5-2.0 mm/yr to the south and 0.5-1.0 mm/yr along its northern extent. An earthquake rupturing the entire length of the offshore system could produce an M7.3 earthquake and potentially impact around 20 million Southern California residents. In late 2013, we acquired the first high-resolution 3D Parallel Cable (P-Cable) seismic survey of the NIRC system as part of the Southern California Regional Fault Mapping project. These data were collected on the continental shelf and slope near the midpoint of the fault system offshore San Onofre and San Clemente, California. Analysis of these high-resolution data has allowed us to map subsurface deformation and construct a geochronology of strain partitioning due to fault segmentation and step-overs. For the first time, we have fully imaged a sequence of synform and antiform fault-fold structures in three dimensions and the complex geometry that created these structures. Given the 3.125 m resolution of the 3D data volume in all directions, the transition from a monocline to a fold to a fault is imaged in the crosslines, inlines, and time-slices. This transition is associated with secondary fault splays and step-overs that creates a "cuspate-style" morphology in the time slice acoustic reflectivity, with the horns of the cusp being antiforms and intervening regions of the cusp being synforms. One of the main strands of the NIRC fault bounds these semi-circular patterns of acoustic reflectivity in the time slice. Such imagery allows us to define how fault segments interact laterally and at depth and the importance of small step-overs and secondary fault splays in how deformation is communicated to neighboring faults. We will present images of this fault-fold sequence by sequentially peeling back the crosslines for a given time slice, then peeling back the inlines, and finally shifting the time slices for a true 3D examination of this fault-fold structure. We will conclude by showing how this fault architecture shapes the continental margin in Southern CaliforniaSupport for this project was provided by Southern California Edison (SCE)Peer Reviewe