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Abstract:
We present an attenuation model for midperiod Rayleigh waves in Central Asia and surrounding regions. This model is defined by maps of attenuation coefficient across the region of study in the period band 14–24 s. The model is constructed to characterize the regional variations in attenuation of seismic waves in the crust, which are related to the tectonic history of the studied territory, to calibrate the regional surface-wave magnitude scale, and to extend the teleseismic 'surface-wave magnitude – body wave magnitude' (Ms-mb) discriminant to regional distances. The construction of the model proceeds in three stages. The first stage in model construction is the measurement of Rayleigh wave spectral amplitudes. We collected and processed waveform data for 200 earthquakes occurring from 2003 to 2006 inside and around Eurasia, and used records of about 135 broadband permanent and temporary stations. This data set provided a sufficient number of spectral amplitude measurements between 14 and 24 s periods for the construction of two–dimensional tomographic maps of attenuation coefficients. At the second stage of the work, the integral of attenuation coefficients along given paths is estimated using both inter-station measurements and single-station measurements corrected for source and receiver terms. The third stage includes the refining of source parameters, recalculation of attenuation coefficient integrals after this refinement, grooming of resulting coefficients, and multistage tomographic inversion of the data. Tomographic maps for the set of periods from 14 to 24 s, which exhibit clear correlation with geology and tectonics of the territory under study, were obtained. Validation of these maps using the inter-station measurements confirms their accuracy in predicting the observations.
