Focal depths and fault plane solutions of earthquakes and active tectonics of the Himalaya

Abstract

We have compared synthetic seismograms with long‐period body waves for nine earthquakes with epicenters in the Himalayan arc to determine depths of foci and to improve fault plane solutions. Focal depths are shallow (10–20 km). Inferred slip vectors are locally perpendicular to the mountain range; they plunge very gently (∼10°( in the eastern sections of the range and more steeply (∼25°) in western sections. Assuming India to be a rigid plate, the radially oriented slip vectors imply that southern Tibet extends at about half the rate of underthrusting in the Himalaya and therefore probably at about 5–10 mm/yr. The shallow depths and gentle dips of the fault planes, at least for the events in the eastern half of the range, are consistent with coherent underthrusting of the Indian plate beneath, at least, the Lesser Himalaya. The steeper dips of fault planes in the western part of the arc might reflect deformation of the overriding thrust plate or simply a steepening of the main underthrusting zone beneath the Greater Himalaya.