abstract

Upper Mantle velocity structure in the Hindukush region has been determined from the P- and S-wave travel times of 28 deep earthquakes making use of a new analytical method given by Kaila (1969). From a depth of 45 to 230 kms, the present analysis reveals a continuous linear increase of P-wave velocity from 8.21 to 8.52 km/sec. For S waves, however, the velocity increases linearly from 4.58 km/sec at a depth of 85 kms to 4.77 km/sec at 230 kms depth. Upper mantle velocities in the Hindukush region are found to be considerably higher in comparison to those for other regions of the Earth. Within the accuracy of the velocity determination from the present method, no inferences can be drawn regarding the existence or otherwise of the low-velocity channel in this region.

Calibration curves for focal depth determination in the Hindukush region are also drawn. The accuracy of focal depth determination from these calibration curves is of the same order as that obtained in the focal depths determined by making use of pP, sS and other reflected phases.

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