Amitabh Sinha
The Indian Express
May 13, 2015
Tuesday’s 7.3 quake was the biggest of them all but about five times weaker in terms of energy released compared to last month’s earthquake.
Tuesday’s quake was another ‘aftershock’ of the April 25 earthquake that measured 7.8 on the Richter scale, scientists said. More than 80 ‘aftershocks’ of magnitude 4 and above have occured since last month’s earthquake. Tuesday’s 7.3 quake was the biggest of them all but about five times weaker in terms of energy released compared to last month’s earthquake.
It was centred around a place 18 km southeast of Kodari town on the Nepal-China border, and originated 15 km below earth’s surface, according to the US Geological Survey. The place is 76 km northeast of Kathmandu.
The area around Kodari has seen the maximum number of aftershocks in the last three weeks. Lamjung, the epicentre of the April 25 earthquake, is about 160 km west of Kodari.
“Aftershocks can come in a large area along a faultline, depending on the strength of the main quake. For a quake as strong as the one on April 25, aftershocks are expected in an area of 100 km radius of the main epicentre,” Harsh Gupta, former director of the Hyderabad-based National Geophysical Research Institute, said.
Almost all significant aftershocks of the April 25 earthquake have been towards the east of Lamjung, mostly concentrated in the area between Kathmandu and Kodari, a town on the Tibet border.
“It seems that the eastern side of the main central faultline running through Nepal has become a weak zone. The aftershock activity has intensified in this region and a readjustment of forces seems to be still going on,” Ajay Paul of the Dehradun-based Wadia Institute of Himalayan Geology said.
Tuesday’s earthquake triggered its own series of aftershocks. Six big aftershocks, measuring more than 5 on the Richter scale, had come within a couple of hours of the 7.3 magnitude quake.
Scientists said it was crucial for the Nepal administration to keep people away from buildings which had developed cracks or were partially damaged in the April 25 quake, as these would be the first to collapse in the aftershocks.
“People need to be kept away from damaged buildings. It is often seen that buildings that remained standing are used as shelters. This needs to be avoided,” Paul said.
Gupta said that considering the magnitude of the quakes that have been hitting Nepal, the country has done well to contain the damage. “The loss of life from the April 25 quake is not expected to go beyond 10,000. Compare it to the Muzaffarabad earthquake of 2005. It was 7.6 on the Richter scale, but more than 75,000 people were killed. Nepal has been conducting earthquake exercises every year, and seems to have benefited from it,” he said.
Gupta said another factor in favour of Nepal has been the soil quality. It does not allow for ‘side amplification’ of the seismic waves on the surface, because of which the damage to buildings has been less, he said.
