Acceleration Attenuation Regularities in the Western Himalayasстатья
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Аннотация:The first stage of seismic impact assessments for engineering calculations of structural earthquakeresistance is seismic hazard assessment. For this, seismological and seismotectonic studies identify seismogenicstructures, then determine the maximum credible magnitudes, recurrence periods, faulting types, distancesbetween selected faults and constructions site, and ground conditions at said sites. After which, it isnecessary to evaluate changes in the acceleration amplitudes with distance in order to reveal the regularitiesin the attenuation of peak ground accelerations. The article discusses various methods for estimating the regularitiesof acceleration attenuation with distance. It is shown that empirical estimates of the mean amplitudesfor various distances have the highest accuracy. No a priori expressions are applied to describe the amplitudeattenuation curves. At the Schmidt Institute of Physics of the Earth (Moscow), using global data, it is shownthat in the engineering range of accelerations, there are three zones distinguished by attenuation and dependenceson the focal mechanism and soil conditions. Each zone has its own attenuation equation. For eachequation, the corresponding standard deviation is estimated. The empirical method for estimating attenuationhas been applied to the Garhwal region of the Himalayan seismic belt. Records of strong movementsacquired during strong earthquakes in this region are used: Dharamsala (April 26, 1986, MW = 5.5), Uttarkashi(October 20, 1991, MW = 6.8), and Chamoli (March 28, 1999, MW = 6.5). An attenuation curve has beenplotted for the Garhwal region. The empirical data are approximated by the found attenuation equations witha standard deviation of about 50% versus 100% by the semiempirical method. The question of regional attenuationfeatures in this Himalayan region is considered. The results are useful in assessing seismic hazard/seismicrisk in the Himalayas.Keywords: peak ground acceleration, magnitude, distance, focal mechanism, ground conditions, attenuation,strong ground motion, seismotectonics, Western Himalayas, Garhwal