HR: 1330h
AN: S22B-0458    [PDF]
TI: A tomographic method to calculate Lg Q across the continental US
AU: * Wesson, R
EM: rwesson@usgs.gov
AF: USGS, 1711 Illinois St., Golden, CO 80401 United States
AU: McNamara, D
EM: mcnamara@usgs.gov
AF: USGS, 1711 Illinois St., Golden, CO 80401 United States
AU: Benz, H
EM: benz@usgs.gov
AF: USGS, 1711 Illinois St., Golden, CO 80401 United States
AU: Frankel, A
EM: afrankel@usgs.gov
AF: USGS, 1711 Illinois St., Golden, CO 80401 United States
AB: Lg attenuation studies are generally successful in discrete regions with a good distribution of earthquakes and recording stations. In such regions ray-path coverage is adequate to resolve a 1D average Q. In our attempt to describe the spatial variation of Lg attenuation throughout the continental United States, we found numerous regions with inadequate coverage due to a limited number of earthquakes and recording stations. To solve this problem we have developed a tomographic method to compute frequency dependent Lg Q, that enables us to use ray-paths that may originate or end outside of a particular region. Fourier amplitude spectra of Lg phases (windowed from 3.7-3.0km/s), recorded at high frequencies (0.5-8Hz), were used to determine regional frequency-dependent attenuation. We divided the continental US into 5 degree cells and solved for source, and station terms for each ray-path and Q-values for each cell using a singular value decomposition (SVD) procedure in five frequency bands (0.75, 1.5, 3.0 and 6.0 Hz). We collected broadband data for over 2500 Lg source-station paths throughout the United States from U.S. National Seismograph Network (USNSN), Advanced National Seismic System (ANSS), Canadian National Network and cooperating stations. Path lengths range from 150 to 4000 km. In regions where we have overlap, our calculated values of Lg Q closely match those previously determined from the analysis of data from discrete regions. The current data set is adequate to resolve the gross distribution of Lg Q across the continental US, with low Q in the West, high Q in the East and well resolved transition values in previously poorly described regions.
DE: 7200 SEISMOLOGY
DE: 7205 Continental crust (1242)
DE: 7212 Earthquake ground motions and engineering
SC: Seismology [S]
MN: 2003 Fall Meeting