High-Resolution Marine Seismic Reflection Data From the San Francisco Bay Area, USGS/OFR 00-494

Marine seismic reflection data are used to image and map sedimentary
and structural features of the seafloor and subsurface. These data
are useful in mapping faults (such as the San Andreas and Hayward
Faults) where they pass under the waters of the San Francisco Bay, and
in assessing other submarine geologic characteristics and features.
Particularattention was devoted to investigating the offshore
confluence of the San Andreas and San Gregorio fault zones. These
data were collected under the auspices of the auspices of the Central
California/San Francisco Bay Earthquake Hazards Project of the Western
Coastal and Marine Geology Program. Further information concerning the
objectives and efforts of this project may be found at:
"http://walrus.wr.usgs.gov/earthquakes/cencal/"

This report consists of two-dimensional marine seismic reflection
profile data from the San Francisco Bay area. These data were
acquired between 1993 and 1997 with the Research Vessels David
Johnston and Robert Gray. The data are available in a variety of
formats, including binary, postscript and GIF image. Binary data are
in Society of Exploration Geologists (SEG) SEG-Y format and may be
downloaded for further processing or display. Reference maps and GIF
images othe profiles may be viewed with your Web browser. Seismic
reflection profiles are acquired by means of an acoustic source
(usually generated electromagnetically or with compressed air), and a
hydrophone or hydrophone array. Both elements are typically towed in
the waterbehind a survey vessel. The sound source emits a short
acoustic pulse, which propogates through the water and sediment
columns. The acoustic energy is reflected at density boundaries (such
as the seafloor or sediment layers beneath the seafloor), and detected
at the hydrophone. As the vessel moves, this process is repeated at
intervals ranging between 0.5 and 20 meters depending on the source
type. In this way a two-dimensional image of the geologic structure
beneath the ship track is constructed.