HR: 1340h
AN: S43A-1057    [Abstracts]
TI: Recalibrating M_L for the California Integrated Seismic Network
AU: * Hellweg, M
EM: peggy@seismo.berkeley.edu
AF: University of California Berkeley, Berkeley Seismological Laboratory #4760, Berkeley, CA 94720, United States
AU: Uhrhammer, R
EM: bob@seismo.berkeley.edu
AF: University of California Berkeley, Berkeley Seismological Laboratory #4760, Berkeley, CA 94720, United States
AU: Hutton, K
EM: kate@gps.caltech.edu
AF: California Institute of Technology, California Seismological Laboratory, Pasadena, CA 91125, United States
AU: Walter, A
EM: awwalter@usgs.gov
AF: United States Geological Survey, 525 South Wilson Ave., Pasadena, CA 91106-3212, United States
AU: Lombard, P
EM: lombard@seismo.berkeley.edu
AF: University of California Berkeley, Berkeley Seismological Laboratory #4760, Berkeley, CA 94720, United States
AU: Hauksson, E
EM: hauksson@gps.caltech.edu
AF: California Institute of Technology, California Seismological Laboratory, Pasadena, CA 91125, United States
AB: Since Richter (1935) and Gutenberg and Richter (1942) developed the local magnitude scale using records from Wood-Anderson seismographs, it has been used to describe event sizes in the catalogs of both northern and southern California (NC and SC). With each change in instrumentation and addition of a station, careful calibration procedures were necessary to ensure catalog continuity, although different amplitude decay functions (logA₀) have been used in each region. In the past 10 years, many broadband stations and strong motion stations have been added to the networks in NC and SC, and efforts are underway to unify earthquake reporting for the state. We have collected data from 180 earthquakes in all of California, from nearly 1000 horizontal channels (described by station-network-channel-location, or SNCL) from the AZ, BK, CI and NC networks. Synthetic Wood-Anderson amplitudes were measured from each channel's trace by decovolving the instrument response and convolving the response of a Wood-Anderson seismograph (Uhrhammer et al, 1996). For each event, differences for all SNCL pairs were calculated, giving a dataset with more than 5 million observations. The differences were simultaneously inverted to determine a correction for each SNCL, dM_L, and a logA₀ that is valid statewide. To ensure consistency with past magnitudes determined in NC and SC the inversion was constrained by two factors: (1) logA₀(100 km) = -3; (2) dM_Ls for station BKS sum to zero. We have produced a set of dM_Ls and a logA₀ function for distances from 1 to 500 km which should be valid in the entire state. We are validating the new values with existing events to ensure the consistency with current magnitude determinations.
DE: 7200 SEISMOLOGY
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7294 Seismic instruments and networks (0935, 3025)
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2007 Fall Meeting