Toward a Rayleigh Wave Attenuation Model for Central Asia and Surrounding Regions

We report on progress toward an attenuation model for short-period (10-20 s) Rayleigh waves in Central Asia and surrounding regions. This model will be defined by maps of attenuation across the region of study in the specified period band. The model is designed 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 (Marshall and Basham, 1971; Bonner et al., 2006; Russell, 2006). Work is progressing in three stages: (1) data accumulation and amplitude measurements, (2) estimation of attenuation coefficients, and (3) tomographic inversion of attenuation data. The first stage in model construction was the measurement of Rayleigh wave spectral amplitudes. To overcome inherent difficulties due to multipathing and scattering of short-period surface waves we applied the Surface Wave Amplitude Measurement Tool (SWAMTOOL) designed at Los Alamos National Laboratory (LANL) (Yang et al., 2005), which incorporates dispersion analysis, phase-matched filtering, and additional means to estimate the quality and reliability of the measurements. We enhanced SWAMTOOL by providing different options for phase-matched filtering of surface wave signals (Levshin et al., 2006). We collected and processed waveform data for 200 earthquakes occurring throughout 2003-2006 inside and around Eurasia. The records of about 140 broadband permanent and temporary stations were used. The existing broadband station distribution and the pattern of seismicity provided sufficient number of spectral amplitude measurements between 12 and 20 s periods for the construction of the two-dimensional (2-D) tomographic maps of attenuation coefficients. Measurements at periods below about 12 s are too scarce for tomographic inversion. Presented at the Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies Conference (29th) held in Denver, CO on 25-27 September 2007. Published in the Proceedings of the Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies Conference (29th), p111-122, September 2007. The original document contains color images.