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High-Resolution Seismic-Reflection and Marine-Magnetic Data from Offshore Central California—San Gregorio to Point Sur

Introduction

Between 2009 and 2012, the U.S. Geological Survey collected high-resolution seismic-reflection data on four surveys (S-N1-09-MB, S-15-10-NC, S-06-11-MB, and S-04-12-MB) and marine-magnetic data on one survey (S-06-11-MB), offshore of central California between San Gregorio and Point Sur (figure 1). The composite survey area spans about 120 km of the coast and includes all of California's State Waters, including Monterey Bay. The survey area includes the mouth and inner portion of Monterey submarine canyon and lies entirely within the Monterey Bay National Marine Sanctuary. Most data were collected aboard the U.S. Geological Survey R/V Parke Snavely. Cumulatively, approximately 1,410 km of seismic-reflection lines and 460 km of marine-magnetic profiles were acquired.

The study area has particular interest for environmental and geologic hazards considerations and has been the focus of significant recent oceanographic and geologic research (Eittreim and Noble, 2002). An understanding of the region's ecosystems and how they function is fundamental to effective stewardship of California's State Waters and the Monterey Bay National Marine Sanctuary (Eittreim and others, 2002). The need for accurate characterization of the seafloor and its substrate, including sediment distribution and thickness as revealed by high-resolution seismic-reflection data, is important for building such an understanding, particularly of the region's benthic ecosystem dynamics.

The study area is cut by active faults, most notably the San Gregorio Fault and the Monterey Bay Fault (Greene and others, 2002). The right-lateral San Gregorio Fault is one of the major strike-slip faults in the widely distributed transform plate boundary along the west coast of North America (Dickinson and others, 2005). This fault system extends along the California Coast for about 400 km from Point Arguello northward to Bolinas and has an estimated slip rate of 3 – 7 mm/yr (Wills and others, 2008). The Monterey Bay Fault either converges with or is truncated by the San Gregorio Fault in northern Monterey Bay. The high-resolution seismic-reflection and marine magnetic data collected in these surveys provide detailed information on shallow geologic structure and recent deformation that will be important in further understanding these faults and in improving earthquake hazard assessments.

Finally, these geophysical data will contribute to a range of geologic and habitat map products that will be used for a variety of coastal and marine spatial-planning applications.