Stress causes chain reaction
Print Edition
THE earthquake that struck Nepal yesterday, 17 days after the one in April, is part of a chain reaction in a notorious seismic hotspot, scientists said.
Like buttons popping off one by one from a shirt that is ripped open, a large quake displaces stress to another part of a fault, causing it to rupture, they said.
“Large earthquakes are often followed by other quakes, sometimes as large as the initial one,” said Carmen Solana, a volcanologist at Britain’s University of Portsmouth.
“This is because the movement produced by the first quake adds extra stress on other faults and destabilizes them,” she told the Science Media Centre, a not-for-profit organization based in London.
“It is a chain reaction.”
Yesterday’s quake hit 76 kilometers east of the Nepalese capital Kathmandu, followed around half an hour later by another of 6.3 magnitude.
The April 25 quake occurred a similar distance west of Kathmandu.
Both events happened on the same fault, where the Indian and Eurasian plates of the Earth’s crust meet, bumping and jostling.
“Since the first earthquake in April, aftershocks have been migrating more or less southeastward,” Nigel Harris, a professor of tectonics at Britain’s Open University, told the SMC.
“There has been a rip in the underlying plate which has suddenly moved west to east, and this second earthquake is an extension of that process.”
Both quakes were shallow, which means that ground shaking is far greater than with those that occur at depth, the scientists said.
Pascal Bernard, a seismologist at the Institute for Planetary Physics in Paris, said aftershocks in the region were unlikely to be greater than 5.0 magnitude.
Eastern Nepal was last hit by an 8.1-magnitude quake in 1934. Around 10,700 people were killed.
“This means that pressure between the two tectonic plates in this region has significantly eased,” Bernard said.
At the interface of the two plates, the Indian plate is riding upwards at around two centimeters a year.
The movement is not smooth but rather laden with friction, leading to sharp and potentially destructive jolts as stress builds up.
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