HR: 0800h
AN: G21A-0118    [Abstracts]
TI: Comparison of Estimates of Coseismic Displacement From the 2003 M 6.5 San Simeon Earthquake
AU: * King, N E
EM: nking@usgs.gov
AF: U. S. Geological Survey, 525 S. Wilson Ave., Pasadena, CA 91106 United States
AB: Estimation of crustal deformation requires trading off solution precision and latency. Between large earthquakes the relative station velocities of southern California stations are small, on the order of a few mm/yr, and the deformation across the entire region is about 50 mm/yr. Estimation of such interseismic crustal deformation rates requires the use of the best GPS software, precise orbits which are available with a delay of one week, and reference frame stabilization; such processing strategies yield precisions of about 1 to 2 mm in the horizontal and about 3 to 4 mm in the vertical. Coseismic offsets for large earthquakes, however, are tens or hundred of mm, or more, for stations near the epicenter, and it is possible to sacrifice a few mm of precision to obtain a rapid solution. Such rapid estimates are useful to both scientists and emergency response agencies. The M 6.5 San Simeon, California, earthquake occurred on December 22, 2003, at the northern edge of the Southern California Integration GPS Network (SCIGN). The nearest station (CRBT) was 34 km from the epicenter, and its horizontal displacement was about 43 mm to the south and 35 mm to the west. The U.S. Geological Survey (USGS), the Scripps Institution of Oceanography, the Massachusetts Institute of Technology (MIT), and the Jet Propulsion Laboratory (JPL) estimated the coseismic displacements for the SCIGN stations. These groups used different software, stations, orbits, processing strategies and parameters. After obtaining rapid solutions, the groups re-analyzed the data using better orbits and more time-consuming processing strategies. Mean differences between pairs of solutions range from sub-mm to 4.5, 6.1, and 8.3 mm in the north, east, and vertical, respectively. Estimates of the coseismic displacement of station CRBT differed by up to 7.3, 5.2, and 10.1 mm in north, east, and vertical components, respectively. Otherwise identical processing with the IGS ultrarapid and precise orbits yielded differences of 0.3, 0.1, and 4.9 mm in the north, east, and vertical; these differences are minor compared to the coseismic signal.
DE: 1242 Seismic deformations (7205)
DE: 1243 Space geodetic surveys
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting