HR: 0800h
AN: S41A-0234    [Abstracts]
TI: Spatial Variation of Surface Wave Q and Body Wave t* in North America
AU: * Hwang, Y
EM: ykhwang@umich.edu
AF: Department of Geological Sciences University of Michigan, 2534 C. C. Little Building 1100 North University Ave., Ann Arbor, MI 48109, United States
AU: Ritsema, J
EM: jritsema@umich.edu
AF: Department of Geological Sciences University of Michigan, 2534 C. C. Little Building 1100 North University Ave., Ann Arbor, MI 48109, United States
AB: We estimate the spatial variation of the seismic parameter t* using teleseismic (30°--90°) P wave recordings of about 300 deep (> 200 km) earthquakes at broadband stations in North America. We determine the P wave spectral ratio R_ij for about 600,000 station pairs i-j with high signal-to-noise ratio P wave signals. The linear fit to lnR_ij between f= 0.1--1.0 Hz is measured to estimate differential Δt* assuming that lnR_ij is proportional to π fΔt* (e.g., Aki and Richards, 1980). The measurements are inverted for t* at each station by least-squares inversion. Preliminary inversions indicate that the variation of t* correlate with the tectonic terrains of North America. Predominantly low values of t* are obtained for stations in the Canadian Shield and high t* values in the North American Cordillera. This variation is similar to Q variations inferred from global surface wave amplitude data (e.g., Dalton and Ekström, 2006), suggesting that intrinsic attenuation is the common cause. We will discuss the robustness of our t* estimates (including the effects of scattering on P wave ratios) and make a detailed comparison with surface wave Q maps.
DE: 1734 Seismology
SC: Seismology [S]
MN: 2007 Fall Meeting