HR: 0800h
AN: S21A-0264    [Abstracts]
TI: Earthquake Detection and Location Capabilities of the Advanced National Seismic Network
AU: * McNamara, D E
EM: mcnamara@usgs.gov
AF: USGS - ANSS, 1711 Illinois, Golden, CO 80401 United States
AU: Buland, R P
EM: buland@usgs.gov
AF: USGS - ANSS, 1711 Illinois, Golden, CO 80401 United States
AU: Benz, H M
EM: benz@usgs.gov
AF: USGS - ANSS, 1711 Illinois, Golden, CO 80401 United States
AU: Leith, W
EM: leith@usgs.gov
AF: USGS - ANSS, 1711 Illinois, Golden, CO 80401 United States
AB: We have computed minimum earthquake moment magnitude, Mw, detection thresholds for a 1x1 degree grid across the US using the existing backbone stations of the Advanced National Seismic System (ANSS). For every grid point we compute the minimum Mw for which the P phase should be detectable by at least five ANSS stations. Detection is declared at a station when body wave power levels produced for a given Mw are above the frequency dependent 80th percentile noise level for the station. Noise levels were determined in a previous study from probability density functions of noise spectra computed for each ANSS backbone station (McNamara and Buland, 2004). To model event power levels, earthquake moment, Mo, is computed as a function of apparent corner frequency using the source scaling formulas of Brune (1970, 1971). The apparent corner frequency is the frequency at which body wave spectral amplitudes are maximum as a result of attenuation and short period filters applied during NEIC phase picking. The corresponding moment magnitude, Mw, is computed after Kanamori (1977). Body wave amplitudes are then computed for each station depending on the distance and attenuation along each raypath. Amplitude is then converted to power (dB) and compared to station noise levels. The fifth lowest power, above station noise levels then corresponds to the minimum earthquake magnitude for that particular grid point. Our theoretical minimum Mw threshold compares favorably to magnitude thresholds determined from USGS PDE catalogs. We also model the regional variation in event location improvement with the installation of planned ANSS backbone stations. Results from this study are useful for characterizing the performance of existing ANSS broadband stations, for detecting operational problems, and should be relevant to the future siting of ANSS backbone stations. Results from this analysis are also used to optimize the distribution of ANSS regional network stations.
DE: 7294 Instruments and techniques
DE: 7299 General or miscellaneous
DE: 7203 Body wave propagation
SC: Seismology [S]
MN: 2004 AGU Fall Meeting