HR:     0830h
AN:     G71G-05
TI:     The Deformation Field of the Pacific--North America Plate
        Boundary Zone in Northern California from Geodetic Data, 1973--1998
AU:     *Murray, M H
EM:     mmurray@pangea.stanford.edu
AF:     Geophysics Dept.,
        Stanford Univ. Stanford, CA 94305-2215  
AU:     *Murray, M H
EM:     mmurray@pangea.stanford.edu
AF:     Seismological Laboratory,
        Univ. of California Berkeley, CA 94720-4760  
AU:     Prescott, W H
EM: 
AF:     U.S. Geological Survey Menlo Park, CA 94025-3491  
AU:     B\"urgmann, R 
EM: 
AF:     Seismological Laboratory,
        Univ. of California Berkeley, CA 94720-4760  
AU:     Freymueller, J T
EM: 
AF:     Geophysical Instit.,
        Univ. of Alaska Fairbanks, CA 99775-7320  
AU:     Segall, P 
EM: 
AF:     Geophysics Dept.,
        Stanford Univ. Stanford, CA 94305-2215  
AU:     Svarc, J 
EM: 
AF:     U.S. Geological Survey Menlo Park, CA 94025-3491  
AU:     Williams, S D
EM: 
AF:     IGPP,
        Univ. California San Diego La Jolla, CA 92093-0225  
AU:     Lisowski, M 
EM: 
AF:     U.S. Geological Survey,
        Hawaiian Volcano Obs. HI 96718  
AU:     Romanowicz, B 
EM: 
AF:     Seismological Laboratory,
        Univ. of California Berkeley, CA 94720-4760  

AB:     We combine geodetic observations collected over the last
        25 years to determine the crustal deformation field of the
        Pacific--North America plate boundary zone in northern California.
        We use Geodolite trilateration (EDM) measurements collected by
        the USGS from 1973 to 1989, very-long-baseline interferometry
        (VLBI) measurements collected by NASA from 1983 to 1992, and
        Global Positioning System (GPS) measurements collected
        by the USGS, NGS, and several university research groups since
        1985, including 35 sites of the Bay Area Regional Deformation
        (BARD) permanent GPS network.
        Solutions with weak coordinate constraints derived from these
        observations are combined using Kalman filter techniques to
        minimize biases due to inhomogeneous reference networks.
        We estimate average rates of interseismic deformation
        taking into account co- and post-seismic displacements,
        either estimated or predicted from seismic data,
        due to the 1989 Loma Prieta, 1992 Cape Mendocino,
        and other major earthquakes.
        The resulting deformation field suggests that the
        Sierra Nevada--Great Valley block is tectonically stable and
        that most of the 36 to 40 mm/yr relative motion observed between
        the Sierra Nevada range and the Pacific plate is accommodated
        by right-lateral slip across the San Andreas fault system
        from San Juan Bautista to Cape Mendocino.
        We will present three-dimensional models of surface
        creep and deep slip along the major faults, along
        with their uncertainties, to better characterize rates
        of strain accumulation and provide a more realistic
        assessment of earthquake hazards.
        Preliminary models indicate that north of San Francisco
        both the San Andreas and Ma'acama faults are locked
        to at least 5 km depth with deep-slip rates of 8--25 mm/yr
        (95\% confidence), and thus both pose significant seismic
        hazards in this region.
DE:     8107  Continental neotectonics
DE:     1206  Crustal movements--interplate (8155)
DE:     1208  Crustal movements--intraplate (8110)
SC:     G
MN:     1998 Fall Meeting