An eminent seismologist and professor at the Indian Institute of Technology in Kharagpur has rejected claims that Nepal had received an aftershock of 6.7 magnitude on the Richter scale, nearly 24 hours after earthquake hit the country last Saturday. Professor Sankar K Nath claimed that Sunday’s jolt — felt around 12.45 pm — was a fresh earthquake.
While the epicentre of Saturday’s quake — 7.9 on the Richter scale — was Lamjung, around 80 km northwest of Kathmandu, the epicentre of Sunday’s “aftershock” was 19 km south-southeast of Kodari in Nepal. This is around 150 km away from the Lamjung epicentre.
Nath, who has prepared a report that he will soon submit to the Centre, said: “It was not an aftershock, but a main shock (quake) triggered by the release of stress accumulated from Saturday’s earthquake. An aftershock cannot take place outside the source and is always recorded within 50 to 100 sq km of the epicentre of the main shock.”
“The second main shock was followed by two aftershocks measuring 5 on the Richter scale. According to data received, the epicentre of the Kodari quake was located 17.3 km deep while it was 11 km deep for Saturday’s quake,” he added.
Maintaining that the quake of April 25 has already been followed by over 45 aftershocks, Nath said: “The quake was immediately followed by an aftershock measuring 6.6 on the Richter scale. Since then, the aftershocks have been becoming weaker. Barring a few, all were recorded below 5 and some were even below 4.” After 24 hours of an 7.9 earthquake, during which aftershocks are diminishing in intensity, there cannot be an aftershock of 6.7 on the Richter scale, he explained.
Nath, a Bhatnagar awardee and a professor in the geology and geophysics department, said IIT has 14 stations in Darjeeling and Sikkim to record data of earthquakes. “We have 12 stations in Sikkim and one each in Darjeeling and Siliguri. We will submit the data to the Union Ministry of Earth Sciences where we will state that Saturday’s aftershock was actually a earthquake.”
Even though the Indian Meteorological Department has recorded it as an aftershock, Nath claimed the US Geological Survey (USGS) has recorded it as a “main shock”. The USGS website stated: “An earthquake with magnitude 6.7 occurred near Kathmandu, Nepal at 07:09:08.90 UTC on Apr 26, 2015. This event has been reviewed by a seismologist.”
When contacted, seismologist and Jadavpur University Professor Ranjit Majumdar also termed Sunday’s jolt as a main shock. “It was a fresh earthquake. The strain from the first main shock on April 24 was released, triggering a fresh quake. There may be more such main shocks… A thorough study should be conducted in Bengal, Bihar and Uttar Pradesh,” he said.