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Continent-Wide Maps of Lg Coda Q Variation and Rayleigh-wave Attenuation Variation for Eurasia

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Final rept. 7 Jun 2004-6 Jun 2006

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We present new maps of Lg coda Q and its frequency dependence at 1 Hz Qo and eta, respectively as well as Rayleigh-wave attenuation coefficients at 5, 10, 20 and 50 s across virtually all of Eurasia. Qo is relatively high, 700 or more, in most cratonic regons but is surprisingly low in the Arabian craton 300-450, the Siberian trap portion of the Siberian Platform 450 and the Deccan trap portion of the Indian Platform450-650. It is generally low throughout the Tethysides orogenic belt but there too it displays substantial regional variations 150-400. All major Qo anomalies, and several minor ones, appear to be related to the tectonic history of the Eurasian crust. The four regions with lowest values approximately coincide with four of Eurasias most active concentrations of earthquake activity. Comparison of the new Qo map with continent-wide maps of long-period Rayleigh-wave phase velocities, temperatures, subducted lithosphere and crustal strain lead us to infer that fluids, originating by hydrothermal release from subducting lithosphere or other upper mantle heat sources largely produce the observed variations of Qo across Eurasia. We estimated Rayleigh-wave attenuation coefficients across Eurasia, at periods of 5, 10, 20 and 50 s, using mapped values for Qo, eta and an empirically derived multiplicative factor for eta. 5 and 10 s attenuation values clearly show several attenuation maxima that are with thick accumulations of sediment, whereas the longer period attenuation, in most cases, mirror the Qo map. Differences, however, occur in some regions because because of high or low eta values.

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  • Geography
  • Radiofrequency Wave Propagation

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