HR: 0800h
AN: S21A-0238    [Abstracts]
TI: A Three-dimensional Geologic Model of the Hayward-Calaveras Fault Junction
AU: * Watt, J T
EM: jwatt@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Graymer, R W
EM: rgraymer@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Simpson, R W
EM: simpson@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Ponce, D A
EM: ponce@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Jachens, R C
EM: jachens@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Phelps, G A
EM: gphelps@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AU: Wentworth, C M
EM: cwent@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025, United States
AB: We present a 3D geologic model depicting the Hayward-Calaveras Fault junction as a complex network of faults at the surface and as a single through-going fault below about 5 km. Deep seismicity suggests a simple connection between the southern Hayward and central Calaveras Faults, whereas geologic mapping at the Earth's surface shows a complex zone of deformation between the fault traces. Such a complicated fault junction represents a challenge for 3D geologic modeling. Newly relocated earthquake hypocenters for the San Francisco Bay region have improved the precision of mapping fault planes, and integrated analysis of multiple datasets in two and three-dimensions has improved the characterization of subsurface geologic and geophysical contacts. In particular, geophysical modeling of magnetic mafic and ultramafic rocks, such as gabbro and serpentinite bordering the southern Hayward Fault, allows the complex structure of these units to be mapped in the subsurface where the southern Hayward and central Calaveras Faults converge. The new 3D geologic model can be used as a basis for earthquake process modeling such as finite element modeling and local and regional ground motion simulations, which will aid in further characterizing the potential seismic hazard along the Hayward-Calaveras fault system. The increased length of a combined southern Hayward and central Calaveras Fault rupture could generate an earthquake greater than M7 based on magnitude-area relationships, posing a significant seismic hazard to the San Francisco Bay region.
DE: 0545 Modeling (4255)
DE: 0920 Gravity methods (1219)
DE: 0925 Magnetic and electrical methods (5109)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8002 Continental neotectonics (8107)
SC: Seismology [S]
MN: 2007 Fall Meeting