Major Earthquake Hits Nepal

This map shows the projected intensity of shaking near the quake's epicentre, which is marked with a star.

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A magnitude 7.8 earthquake hit just 80 kilometers northwest of Kathmandu on April 25, crumbling buildings and devastating much of the city. The ground shook well beyond Nepal’s borders, into Tibet and northern India, in one of the worst natural disasters to strike the Himalayas in years; thousands of people are feared dead. Here,  takes a look at the geological and social circumstances that combined to make the Nepal quake so deadly.

Why did the quake happen?

The April 25 quake was relatively shallow—just 15 kilometers deep, according to the U.S. Geological Survey (USGS). Preliminary data suggest that the Himalayan fault broke a chunk of crust some 150 to 200 kilometers long, says Susan Hough, a seismologist at the USGS offices in Pasadena, Calif., who has worked in Nepal.

Were scientists expecting it?

Even so, the April 25 earthquake was a little smaller and farther east of what some had expected. It occurred close to the site of a magnitude-8.1 earthquake in 1934 that killed more than 10,000 people and sent buildings in northern India sinking more than a meter deep into the ground.

How bad is the damage?

Officials in Nepal estimate that at least 1,400 people are dead, and that number is likely to rise in the days to come. On Mount Everest, the earthquake triggered an avalanche that swept into the base camp. At least 10 people are thought to have been killed on the mountain.

Why weren’t people more prepared?

In Kathmandu, older buildings were often constructed from unreinforced masonry, which cannot withstand the ground shaking from a quake so nearby. The area is also growing more urban, and many newer buildings have been built together in dense neighborhoods without structural reinforcements.

“It’s not a problem of ignorance, it’s a problem of resources,” Hough says. “People are building houses to live in with the resources that they have. They can’t afford rebar and engineering.”

What happens next?  on April 25, 2015.