Late Miocene-Quaternary fault evolution and interaction in the southern California Inner Continental Borderland

Changing conditions along plate boundaries are thought to result in the reactivation of preexisting structures. The offshore southern California Borderland has undergone dramatic adjustments as conditions changed from subduction tectonics to transform tectonics, including major Miocene oblique extension, followed by transpressional fault reactivation. However, consensus is still lacking about stratigraphic age models, fault geometry, and slip history for the near-offshore area between southern Los Angeles and San Diego (California, USA). We interpret an extensive data set of seismic reflection, bathymetric, and stratigraphic data from that area to determine the three-dimensional geometry and kinematic evolution of the faults and folds and document how preexisting structures have changed their activity and type of slip through time. The resulting structural representation reveals a moderately landward-dipping San Mateo–Carlsbad fault that converges downward with the steeper, right-lateral Newport-Inglewood fault, forming a fault wedge affected by Quaternary contractional folding. This fault wedge deformed in transtension during late Miocene through Pliocene time. Subsequently, the San Mateo–Carlsbad fault underwent 0.6–1.0 km displacement, spatially varying between reverse right lateral and transtensional right lateral. In contrast, shallow parts of the previously identified gently dipping Oceanside detachment and the faults above it appear to have been inactive since the early Pliocene. These observations, together with new and revised geometric representations of additional steeper faults, and the evidence for a pervasive strike-slip component on these nearshore faults, suggest a need to revise the earthquake hazard estimates for the coastal region

Evidence for widespread creep on the flanks of the Sea of Marmara transform basin from marine geophysical data

"Wave" fields have long been recognized in marine sediments on the flanks of basins and oceans in both tectonically active and inactive environments. The origin of "waves" (hereafter called undulations) is controversial; competing models ascribe them to depositional processes, gravity-driven downslope creep or collapse, and/or tectonic shortening. Here we analyze pervasive undulation fields identified in swath bathymetry and new high-resolution multichannel seismic (MCS) reflection data from the Sea of Marmara, Turkey. Although they exhibit some of the classical features of sediment waves, the following distinctive characteristics exclude a purely depositional origin: (1) parallelism between the crests of the undulations and bathymetric contours over a wide range of orientations, (2) steep flanks of the undulations (up to ∼40°), and (3) increases in undulations amplitude with depth. We argue that the undulations are folds formed by gravity-driven downslope creep that have been augmented by depositional processes. These creep folds develop over long time periods (≥0.5 m.y.) and stand in contrast to geologically instantaneous collapse. Stratigraphic growth on the upslope limbs indicates that deposition contributes to the formation and upslope migration of the folds. The temporal and spatial evolution of the creep folds is clearly related to rapid tilting in this tectonically active transform basin

Scale of subglacial to sub-ice shelf facies variability, Eastern Basin, Ross Sea

The Eastern Basin within the Ross Sea records changes in the volume of the West Antarctic Ice Sheet (WAIS). Examination of multibeam data revealed four acoustic facies that vary from west to east in a 900 km2 area. It is hypothesized that these facies, that formed nearly contemporaneously, are the result of differences in proximity to the grounding line and its relationship with the seafloor. The four facies are 1. Mega-Scale Lineation, 2. Slightly-Lineated Ridge Crest, 3. Discontinuous Ridges, 4. Irregular Mounds. These trends were also seen in SCS data, distinctively on the seafloor and mutedly at depth. Through determining the extent of fluctuation in these facies and their distribution in the Ross Sea it will be possible to apply this scale to the core record to determine if facies were generated via global processes or were local in origin

United States Geological Survey Bulletin 1995-Y, Z

From abstract: A complex Neogene history characterizes the offshore Santa Maria basin and the northwest margin of the western Transverse Ranges, California. This history includes the transition from subduction to a transtensional and then transpressional plate boundary, including about 900 of clockwise rotation of the western Transverse Ranges. This report uses seismic reflection data to document the geometry of structures that accommodated this deformation and offshore well data to date and correlate the sediments which were affected by the different tectonic episodes

Post-500 ka and Holocene activity on distributed faults of the North Anatolian Fault system along the southern shelf of Marmara Sea, Turkey

Geodetic monitoring and patterns of seismicity indicate that the Northern Branch of the North Anatolian Fault (NAF) absorbs the majority of the relative motion between the Eurasia and Anatolia plates along the northern Marmara Sea. Nonetheless, historical seismicity documents that the Central Branch of NAF is also hazardous, with earthquakes diffusely occurring in the southern Marmara Sea. In order to better assess the seismic hazards facing large cities along the southern coast, we recently collected geophysical data across the adjacent shelf. These data include closely spaced high-resolution multichannel seismic profiles, sparker seismic profiles, CHIRP sub-bottom profiles, and multibeam bathymetric data. The stratigraphic and structural analyses of this new dataset and prior datasets highlight the geometry of three long faults and many shorter, discontinuous faults. The three longer faults are interpreted as primarily strike-slip fault zones. All the mapped faults are Late Quaternary active and, in fact, many fault segments are Holocene active. Smaller discontinuous faults are present in Gemlik and Erdek bays, some of them clearly active during Holocene time. This pattern of Late Quaternary active faults can account for the well-documented dispersed seismicity on the southern shelf. Based on the lengths of the various fault segments, we estimate that earthquakes with moment magnitude as high as 7.4 may occur along the southern shelf of the Marmara Sea. Therefore, the system of distributed faults that constitutes the Central Branch of the NAF in that area represents a significant seismic hazard for the southern coastal cities

Post-500 ka and Holocene activity on distributed faults of the North Anatolian Fault system along the southern shelf of Marmara Sea, Turkey in Tectonophysics.

Geodetic monitoring and patterns of seismicity indicate that the Northern Branch of the North Anatolian Fault(NAF) absorbs the majority of the relative motion between the Eurasia and Anatolia plates along the northernMarmara Sea. Nonetheless, historical seismicity documents that the Central Branch of NAF is also hazardous,with earthquakes diffusely occurring in the southern Marmara Sea. In order to better assess the seismic hazardsfacing large cities along the southern coast, we recently collected geophysical data across the adjacent shelf.These data include closely spaced high-resolution multichannel seismic profiles, sparker seismic profiles, CHIRPsub-bottom profiles, and multibeam bathymetric data. The stratigraphic and structural analyses of this newdataset and prior datasets highlight the geometry of three long faults and many shorter, discontinuous faults. Thethree longer faults are interpreted as primarily strike-slip fault zones. All the mapped faults are Late Quaternaryactive and, in fact, many fault segments are Holocene active. Smaller discontinuous faults are present in Gemlikand Erdek bays, some of them clearly active during Holocene time. This pattern of Late Quaternary active faultscan account for the well-documented dispersed seismicity on the southern shelf. Based on the lengths of thevarious fault segments, we estimate that earthquakes with moment magnitude as high as 7.4 may occur along thesouthern shelf of the Marmara Sea. Therefore, the system of distributed faults that constitutes the Central Branchof the NAF in that area represents a significant seismic hazard for the southern coastal cities.</p