HR:     08:30h
AN:     G21A-01 INVITED
TI:     Strain Accumulation in the New Madrid Seismic Zone From GPS Data, 1993-1997
AU:     *Kerkela, S 
EM:     stacy@geo.stanford.edu
AF:     Dept. of Geophysics, Stanford Univ. Stanford, CA 94305  United States
AU:     Murray, M H
EM:     mmurray@geo.stanford.edu
AF:     Dept. of Geophysics, Stanford Univ. Stanford, CA 94305  United States
AU:     Murray, M H
EM:     mmurray@geo.stanford.edu
AF:     Seismological Laboratory, Univ. of California Berkeley, CA 94720  United States
AU:     Liu, L 
EM:     lanbo@geol.uconn.edu
AF:     Dept. of Geology & Geophysics, Univ. of Connecticut Storrs, CT 06269  United 
        States
AU:     Zoback, M D
EM:     zoback@geo.stanford.edu
AF:     Dept. of Geophysics, Stanford Univ. Stanford, CA 94305  United States
AU:     Segall, P 
EM:     segall@geo.stanford.edu
AF:     Dept. of Geophysics, Stanford Univ. Stanford, CA 94305  United States
AB:     We have re-surveyed the Caruthersville geodetic network within the
        Marked Tree to Caruthersville (MTC) section of the southern New Madrid
        Seismic Zone during the summers of 1993 and 1997.
        The MTC seismic zone trends NE-SW down the center of the late
        Precambrian--early Paleozoic rift that is the approximate location of
        the great 1811--1812 earthquakes.
        Results from our first survey of the network in 1991, which
        re-occupied triangulation stations previously surveyed in the early
        1950's, showed statistically significant strain accumulation in the
        Caruthersville network.
        We extended this network to the southwest and to the east so that it
        now completely spans the MTC seismic zone, allowing us to better
        resolve the spatial distribution of the strain.
        We analyzed the 1993 and 1997 GPS observations using GAMIT software
        with IGS orbits and obtained relative station coordinates with 4 mm
        repeatability in the horizontal components.
        Preliminary results suggest that the strain rates are spatially
        inhomogeneous within the Caruthersville network and that significant
        shear strain is localized only along the MTC seismicity zone.
        Strain rates in the eastern part of the Caruthersville network,
        which overlies the MTC seismicity zone, are consistent with our 
        previous results. We do not find evidence for significant strain 
        rates to the west of the MTC seismic zone as previously reported,
        but several stations in that region were not re-occupied in both 1993 
        and 1997. 
        Inclusion of the triangulation and reprocessed 1991 GPS data
        will further help to resolve the significance of the observed strain
        and its spatial distribution.
DE:     1208  Crustal movements--intraplate (8110)
DE:     1243  Space geodetic surveys
SC:     G
MN:     1998 Fall Meeting