References and Notes

works against any hypothesis that attributes deep earthquakes in southern Tibet to pro-cesses related to subduction. Large to moderate-sized earthquakes occur at depths of 100 km or more beneath the west-ern Himalayan syntaxis and the western Kunlun Mountains. Such focal depths are likely to be in the mantle, indicating that the uppermost man-tle of the continental lithosphere is strong enough to sustain the accumulation of elastic strain required for causing earthquakes. The thickened crust of Tibet appears to vary in thick-ness by up to 20 km over distances of a few hundred kilometers, so whether every unusually deep earthquake is in the mantle remains uncer-tain. Nonetheless, a bimodal distribution of focal depths, peaking in the shallow crust and near the Moho, strongly suggests that the two seismogenic regions of the continental lithosphere correspond to maxima in mechanical strength