Abstract

This paper is concerned with space–time variations in the attenuation of shear waves in the Hindu Kush area. We examined the ratios of maximum amplitudes in S and P waves (the S/P parameter) obtained from records of deep-focus earthquakes made at the AAK station in 1993–2016 at epicentral distances of ~700–800 km. The dependence of the amplitude on the radiation pattern for S and P waves was taken into account by averaging the S/P parameter over different time spans. Substantial space–time variations in S wave attenuation was found in different depth ranges in the zone of deep-focus seismicity. We show that the lowest attenuation in 2013–2015 prior to the great earthquake of October 26, 2015 (M_w = 7.5, h = 231 km) was observed for hypocenters above the rupture zone, at depths of 151–210 km, while the highest attenuation occurred at depths of 231–270 km. Following the earthquake, the attenuation rapidly decreased at depths of 231–270 km and increased in the depth range of 191–230 km. These effects are hypothesized to have been caused by dehydration of mantle rocks, as well as by migration of deep-seated fluids.

中文翻译：

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印度兴都库什地区短时剪切波衰减场的时空变化

摘要

本文关注兴都库什地区剪切波衰减的时空变化。我们检查了S和P波的最大振幅比（S / P参数），这些记录是从1993年至2016年在AAK站的震中距离约为700-800公里的深焦点地震记录中获得的。通过在不同时间跨度上平均S / P参数，可以考虑振幅对S和P波辐射方向图的依赖性。在深焦点地震活动区的不同深度范围内发现了S波衰减的时空变化。我们表明，在2015年10月26日大地震之前，2013-2015年的衰减最小（M _w = 7.5，h断裂带上方震源在151-210 km处观察到= 231 km），而最大衰减发生在231-270 km处。地震后，衰减在231–270 km的深度迅速减小，而在191–230 km的深度范围增加。据推测，这些影响是由地幔岩石的脱水以及深层流体的迁移引起的。