Hundreds die in Afghanistan quake.

Hundreds die in Afghanistan quake

The magnitude 6.8 earthquale that shook northern Afghanistan on Jan. 31 killed 200 to 400 people in that country and at least 300 in nearby sections of Pakistan, according to waverly Person at the U.S. Geological Survey's National Earthquake Information Center in Golden, Colo. The shock also caused considerable damage and landslides in the bordering Soviet republic of Tadzhikistan, he says.

The quake struck in a mountainous region known as the Hindu Kush, which forms the western extension of the Himalayas. Originating 154 kilometers below the surface, the shock generated seismic waves felt as far away as Delhi, India, about 1,000 km from the epicenter. The Hindu Kush region is one of the few spots around the globe that commonly produce quakes at such depths, says David Simpson, a seismologist at Columbia University's Lamount-Doherty Geological Observatory in Palisades, N.Y. In other seismecally active parts of the world, such as California, faulting generally occurs in the crust, the brittle layer forming the upper 30 or 40 km of the Earth. But the Afghanistan quale emanated from a spot in the underlying mantle, where rock is usually too hot and ductile to produce ground-shaking fractures.

What's special about the Hindu Kush? It lies in the middle of a geologic vise created by a collision between the Indian plate to the south and the Asian plate to the north. During an earlier stage of that collision, an ocean separated the two land masses, but the dense oceanic crust has since sunk down into the Earth as the two plates pushed together. Parts of the sunken crust have apparently remained attached to the plates at the surface, and Simpson suggests last month's earthquake occurred within one such section that sticks hundreds of kilometers down into the mantle.