Aftershocks of the Quetta earthquake of February 18, 1955 (H = 22:48:38 G.M.T.), were recorded at three temporary field stations, 10 to 15 kilometers from the macroseismic epicentre. A spare Willmore seismograph operated in turn at the three stations. From the study of predominant S − P time intervals of aftershocks recorded at the field stations and at the permanent Observatory, velocity of P and depth of focus were calculated on the assumption that (i) Poisson's ratio of rocks is 1/4, thus n = (P − O)/(S − P) = 1.37, and (ii) S − P time intervals of peak frequency were due to aftershocks originating from the same point, probably the focus of the main shock. Velocity of P waves thus calculated was found to be 5.6 km/sec. and the depth of focus about 7 km.

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