HR: 1340h
AN: S13A-1030    [Abstracts]
TI: B-Value Mapping of the Yellowstone Volcanic and Hydrothermal System
AU: * Farrell, J
EM: jfarrell@mines.utah.edu
AF: University of Utah Department of Geology & Geophysics, 135 S. 1460 E. Room 719, Salt Lake City, UT 84112-0111 United States
AU: Husen, S
EM: husen@sed.ethz.ch
AF: Swiss Seismological Service, Technoparkstr. 1 Einsteingebaeude, H29, Zurich, CH-805 Switzerland
AU: Smith, R B
EM: rbsmith@mines.utah.edu
AF: University of Utah Department of Geology & Geophysics, 135 S. 1460 E. Room 719, Salt Lake City, UT 84112-0111 United States
AB: The Yellowstone region is one of the most seismically active areas in the U.S. Cordillera. There are 26,019 earthquakes in the catalog for the years of 1973 - 2003. Recently, the earthquake catalog has been relocated using 3-d velocity models and non-linear, probabilistic earthquake locations. During relocation, coda magnitudes, Mc, were recomputed using a newly derived magnitude equation including newly available instrument calibrations. The relocated earthquake catalog encompasses 19,097 earthquakes between 1984 and 2003 with consistent magnitudes throughout the entire time period. Reliable information on location uncertainties, included in the probabilistic solution to the earthquake location problem, allowed us to select only well-constrained earthquake locations, leaving 9,793 events to map the b-value distribution. Seismicity in the Yellowstone National Park region is characterized by extensive swarms. In order to accurately map b-values in the area, the catalog has to be deswarmed. An algorithm was used that categorized earthquake swarms based solely on interevent times and distances. Using the above algorithm, a total of 55 swarms were identified from 1984 - 2003. These swarms vary in duration from 3 to 83 days; the number of events vary from 20 to 650.After deswarming the catalog, 4,689 events remained. There is no need to additionally decluster the catalog because the mainshock/aftershock pattern of seismicity is not observed in the Yellowstone National Park region. The 597 events triggered by the 2002 Denali Fault earthquake were then removed giving a total of 4,092 independent events in the catalog. Using the deswarmed catalog, we will image the b-values distribution for the Yellowstone National Park region using ZMAP. B-values will be also evaluated using the original - clustered and not relocated - catalog and compared to the results obtained with the selected catalog. This will help us to better understand the effects of dependent events and earthquake locations on the b-value distribution. Variations in b-values can be indicative of material heterogeneity, the applied shear stress, the effective stress, and/or the thermal gradient of an area. In order to distinguish between the different causes, we will compare the b-value distribution with existing crustal tomography results, which will help us to better understand crustral structure and ongoing tectonic processes beneath the Yellowstone National Park region.
DE: 7230 Seismicity and seismotectonics
DE: 7200 SEISMOLOGY
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting