Mapping S-Wave Attenuation Field of the North Tien Shan Region Using Seismogram Coda for Local Earthquakes and Quarry Blasts

Resumo

We have mapped the short-period shear-wave attenuation field in the lithosphere of the North Tien Shan and analyzed seismograms of local earthquakes and quarry blasts, recorded by five stations installed in the area of Almaty and its nearest vicinities (including the site of the WWR-K nuclear reactor). Characteristics of common S coda envelopes for various sectors relative to seismic stations are described. Cross-sections of the attenuation field for the stations considered are constructed. Characteristics of the attenuation field to the north of the Zaili deep fault zone (southern margin of the Kazakh platform) and to the south of it (in mountain areas) are compared. This has allowed us to conclude about the different contents of deep-seated fluids in these areas. The maps of the attenuation field in various depth ranges and at different azimuths for all stations are made. The zones of the highest attenuation, where large earthquake can nucleate, are found. Recommendations are given regarding installation of additional stations in order to provide more operative and accurate determination of epicenter location of a possible earthquake and its magnitude for the safe operation of the WWR-K nuclear reactor.