Continent-Wide Maps of Lg Coda Q Variation and Rayleigh-wave Attenuation Variation for Eurasia
Abstract
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 Platform(450-650). 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 Eurasia's 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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 30, 2007
- Accession Number
- ADA465269
Entities
People
- Brian J. Mitchell
- Lianli Cong
Organizations
- Saint Louis University