Accession Number : ADA259323
Title : Attenuation and Source Studies in Northern Eurasia.
Descriptive Note : Semi-annual technical rept.
Corporate Author : SAINT LOUIS UNIV MO DEPT OF EARTH AND ATMOSPHERIC SCIENCES
Personal Author(s) : Mitchell, Brian J ; Xie, J K
Report Date : 30 Dec 1992
Pagination or Media Count : 46
Abstract : A new inversion method, in which the frequency dependence of shear wave internal friction (Q sub mu to the -1) is allowed to vary with depth, was developed and applied to selected Rayleigh wave attenuation data in the Basin and Range Province of the southwestern United States. Models were further constrained to satisfy observed values of Q and the frequency dependence of Lg waves in that region. Many models can explain those two data sets within their uncertainties, but at 1 Hz most have low values of Q sub mu (50-80) in the upper 8 km of the crust, rapidly increasing values to about 1000 at mid-crustal depths, and decreasing values at greater depths. Models which include a layer of higher Q values (80-150) in the upper few km of the crust, overlying a region of low Q values, cannot be predicted by the data of this study. Models for which the frequency dependence is low (0.0-0.1) in the upper crust best explain the available data. In the lower crust that frequency dependence may be substantial and leads to models in which Q sub mu may be an order of magnitude lower (approx. 100) at a period of 100 s than it is a 1 s ( approx. 1000).
Descriptors : *EARTH CRUST , *SEISMIC WAVES , *INTERNAL FRICTION , FREQUENCY , UNITED STATES , SURFACE WAVES , MODELS , INVERSION , SEISMOLOGY , RAYLEIGH WAVES , TECTONICS , EURASIA , VISCOUS FLOW , ATTENUATION , LAYERS , CRACKING(FRACTURING) , DEPTH , SHEAR STRESSES
Subject Categories : Geology, Geochemistry and Mineralogy
Distribution Statement : APPROVED FOR PUBLIC RELEASE