Seven aftershocks hit NE after massive Myanmar earthquake; experts warn of more

Guwahati, March 29: At least seven aftershocks were felt within five hours of the massive 7.7 magnitude quake that rattled Myanmar and shook the neighbouring areas including the Northeast, and seismologists fear many more such tremors could follow the mainshock. No damage has been reported from the Northeast so far.

“A 7.7 Richter scale quake is a large quake in terms of seismology. It is not surprising as it is a highly seismic zone. Many aftershocks are likely to follow,” seismologist Prof JR Kayal said.

The Sagain fault region has experienced similar large earthquakes, with six other magnitude 7 and larger earthquakes occurring since 1900 within 250-km radius of Friday’s earthquake.

The most recent of these was a magnitude 7.0 earth-quake in January 1990, which caused 32 buildings to fall. A magnitude 7.9 earthquake occurred south of Friday’s earthquake in February 1912. A magnitude 7.7 earthquake in 1988 caused fatalities and was felt in Assam as well.

Friday’s quake occurred as the result of “strike-slip” faulting between the Indian and Eurasian plates.

“There had been some 16-17 large quakes in last 100 years in the region. For example, the 1988 quake occurred at a depth of 110 km and was felt in Manipur and Mizoram, but it did not cause much damage. But today's quake occurred at a shallow depth, so it was devastating,” Kayal said.

He said that a study was required to ascertain if Friday's quake was linked to the ‘swarm’ of quakes in Mizoram reported five years ago. "There are 8-10 quakes of magnitude 5-6 within a few months in Mizoram, which is rare. We need to study if there is some link," Kayal added.

Friday's earthquake was triggered by the causative Sagaing fault 1,200 km east of the Indo-Burma subduction zone. The rupture direction is towards Bangkok, Thailand causing severe damage to structures in the region due to liquefactions and matching of earthquake shaking frequency with the spectral frequency of the structures.

An aftershock of M 7.0 occurred within 12 minutes about 90 Km SW of the mainshock. Seismologist Saurav Baruah said there could be frequent aftershocks in the next one month, and tremors will continue for about a year or so. Barua also said the quake in Sagain fault could “stress trigger” tremors in the Indo-Myanmar subduction zone. The characteristics of such quakes are, however, different and are a result of thrust mechanism, Baruah said, urging people in the region to be alert. A 3.7 quake occurred in Manipur at 6.47 pm on Friday.

“Northeast India also felt this trans-boundary earthquake and aftershocks. The region has a history of M 7 and above quakes like 1956 (M 7.2) and in 1912 (M 7.5),” the National Centre for Seismology said in a report.

At least four earthquakes of more than 4.0 magnitude were recorded in the Indo-Myanmar region on March 5.

The Indo-Burma (Myanmar) Arc subduction zone witnessed two great earthquakes (Mw 8.0 and above in 1897 and 1950) and a total of 25 large earthquakes (Mw more than 7.0) in the past since 1869. The tectonic feature is a continental-scale arc that runs for about 1,300 km and includes parts of Northeast India, Bangladesh, and Myanmar. A magnitude 4.0 quake epicentre in East Garo Hills was also felt in parts of the region at around 1.03 pm, but it was not linked to the Myanmar quake.

- By Rituraj Borthakur