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 (Mw = 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.
Published Version
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