The faultplane technique and the mechanism in the focus of the Hindu Kush earthquakes

Abstract

The mechanism in the focus of the Hindu Kush earthquakes centering at 36½ °N, 70 ½° E and a depth of about 220 km is investigated. The faultplane technique developed by Byerly and Koning and extended by Hodgson is simplified  by using the azimuth and the angle  with the downward vertical in  which the  wave did leave the focus as variables and  not the azimuth and epicentral distance or “ extended epicentral distance”. Compression and diltation data of the P and PKP waves as reported to ISS and BCIS increased with some data as observed in original seismograms or copies of some seismographic stations in the NW.--SE azmiuth are the bases of this study. The use of reflected longitudinal  waves  and the S wave for the same purpose is briefly discussed.

It is found that the earthquakes are caused by a thrust fault movement in the focus. The principal stress component (greatest compression) acts about horizontal in the NW -SE azimuth the smallest stress component (greatest stretching) about vertical somewhat inclined towards SW. The derived stress system is not in contradiction with the about NE-SW trending Hindu  Kush mountain system.