The area stretching across Pakistan into India and Afghanistan is a hotbed for seismic activity that erupts each time the Indian subcontinent slams into Asia. But it's the shallow faults that make these temblors so deadly.
Saturday's magnitude-7.6 quake, centered just outside Pakistan's capital, was about six miles deep, causing buildings to sway in three nations and killing thousands as weak structures tumbled, crushing people under mounds of rubble.
"It's how close you are to where the earthquake initiated, because ground motions fall off very rapidly away from the earthquake," said Harley Benz, a seismologist who runs the United States Geological Survey's National Earthquake Information Center in Colorado.
"Shallow earthquakes are very dangerous because they're very close to the built environment, unless they're in remote areas," he said.
In comparison, a 7.5-magnitude earthquake jolted Peru in September. He said it occurred about eight miles beneath the surface in a more remote area. Only a handful of people died and several hundred homes were destroyed.
The December magnitude-9.0 earthquake that occurred off Indonesia's Sumatra island and spawned a tsunami that killed more than 176,000 people in 11 countries occurred about 18.6 miles below the surface.
The crash between the Indian plate and the Eurasian plate in the latest quake triggered the temblor along a range front that extends about 1,250 miles, Benz said.
