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Experts explain the science behind Saturday’s deadly earthquake A little before noon Saturday in Nepal, a chunk of rock 15 kilometers below the earth’s surface shifted , unleashing a shock wave—described as being as powerful as the explosion of more than 20 thermonuclear weapons—that ripped through the Katmandu Valley. In geological terms, the tremor occurred like clockwork—81 years after the region’s last earthquake of such a magnitude, in 1934. Historical records dating to 1255 indicate the region—known as the Indus-Yarlung suture zone—experiences a magnitude-8 earthquake “approximately every 75 years,” according to a report by Nepal’s National Society for Earthquake Technology. ‘Earthquakes dissipate energy, like lifting the lid off a pot of boiling water. But it builds back up after you put the lid back on.’ —Lung S. Chan, geophysicist at the University of Hong Kong The reason is the regular movement of the fault line that runs along Nepal’s southern border, where the Ind

At 7.8 on the Richter scale, this was a powerful quake – and its source was only 11km below ground Several factors combined to make Saturday’s earthquake in Nepal  such a devastating event. The first was its basic magnitude. At 7.8 on the Richter scale, this was one of the most powerful earthquakes to strike the region in the past 80 years. In addition, it was a shallow event with a source that was only 11km below ground. Nepal earthquake: rescue continues as death toll exceeds 2,500 – the day's updates That has special consequences, according to David Rothery, professor of planetary geosciences at the Open University. “The shallowness of the source made the ground-shaking at the surface worse than it would have been for a deeper earthquake,” he explained. “I’ve seen pictures of poorly constructed old buildings destroyed in Kathmandu, and I’m concerned that in this mountainous region there could have been landslides that might have destroyed or cut off various remote villages.