HR: 08:45h
AN: S21A-04 INVITED     [PDF]
TI: Shear-wave Q and it Frequency Dependence in the Crust of the Middle East and China
AU: * Mitchell, B J
EM: mitchbj@eas.slu.edu
AF: Saint Louis University, Dept. of Earth & Atm. Sci. 3507 Laclede Avenue, St. Louis, MO 63103 United States
AU: Jemberie, A L
EM: ajemberie@memphis.edu
AF: University of Memphis, CERI 3876 Central Avenue, Memphis, TN 38152 United States
AU: Cong, L
AF: Yunnan University, Department of Earth Sciences, Kunming, 10000 China
AB: Models of Q determined using single-station measurements usually have an advantage over methods that use station pairs along a great-circle path in that they are more likely able to utilized relatively short paths, sometimes within a single tectonic province. Waves that travel short paths are therefore less likely to be contaminated by effects of lateral refraction and multipathing, but have the additional requirement that the mechanism and depth of the earthquake used be known. A single-station method that utilizes pairs of amplitude spectra, one corresponding to the fundamental Rayleigh mode and other corresponding to a superposition of higher Rayleigh modes, provides a means to determine models of shear-wave Q at crustal depths. It is especially effective in regions where Q is low. The method has been applied to portions of the Middle East and China and has yielded the lowest values of crustal shear-wave Q yet found in continents. Coverage is best in China, allowing the first detailed maps of shear-wave Q variations at different depths in the crust. In the depth range 0-10 km Q varies between about 40 in the western part of the Tibetan Plateau and about 250 in southeastern China. In the depth range 10-30 km Q varies between about 60 beneath parts of Tibet and about140 in central China. Determinations of the frequency dependence of shear-wave Q almost all lie in the range 0.4-0.7, but are 0.1-0.3 in parts of Tibet where shear-wave Q is low. The regional distribution of Q generally agrees with variations of Q obtained using Lg coda and correlates well with the tectonics of southern Asia.
DE: 3630 Experimental mineralogy and petrology
DE: 7207 Core and mantle
DE: 7218 Lithosphere and upper mantle
DE: 7260 Theory and modeling
DE: 8160 Rheology--general
SC: Seismology [S]
MN: 2003 Fall Meeting