Photo Gallery: Earthquake Devastation in Kashmir >>
The magnitude 7.6 earthquake that shook a broad swath of South Asia on October 8 resulted from the same forces that give rise to the world's tallest mountains, the Himalaya, experts say.
The Earth's crust is broken up into a jigsaw puzzle of plates constantly on the move. Some collide, others drift apart. They all jostle along in fits and starts like uncomfortable strangers in a packed crowd.
In the worst-hit nation, Pakistan, the Indian continental plate to the south is trying to subduct, or dive beneath, the Eurasian plate to the north, said Robert Yeats, a geologist at Oregon State University in Corvallis who studies the region.
This ongoing collision forces the Earth's crust to buckle, producing the Himalaya, Karakoram, Pamirs, and Hindu Kush mountain ranges.
Shallow Faults
The compression of the plates also creates a sinuous array of smaller faults in the upper layers of the Earth's crust, Yeats said. Movements in these shallow faults—known as thrust faults—are responsible for devastating earthquakes.
"The bad thing about crustal earthquakes is [that] when an earthquake [originates] so close to the surface, it just produces very, very strong ground motion," he said.
The October 8 earthquake originated only about 6.2 miles (10 kilometers) deep. Because it was so shallow, the shaking forces were much greater than similar-magnitude earthquakes that occur deeper in the crust, Yeats added.
The shaking triggered massive landslides that buried villages carved into the steep mountainsides. The estimated death toll from the quake currently stands at about 40,000 people.
To build on the rugged Himalayan terrain, villagers dig into a mountain and pile the dug-up dirt and rocks below to create a flat spot.
"What that does is steepen the mountain even more than it originally was. A little shake and the uphill side of the road will likely have rocks that come loose and fall, and the downhill side just slides away completely," said Wayne Pennington, a geologist at Michigan Technological University in Houghton.
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