Seismic activity increasing in Northeast

On an average, the Northeast was rocked by an earthquake every 10 days in 2009 as statistics pointed to increasing seismic activity in the region.

Records with the Central Seismological Observatory in Shillong said 34 'quakes of light and moderate intensity were felt in the region including one of magnitude 6.2 (on September 21), the biggest in the last 20 years.

The region had witnessed 26 earthquakes each in 2008 and 2007, while it was 23 in 2006. However, in 2005, the number of earthquakes was 38.

“The reason behind the increase is that tsunami had occurred towards the end of December, 2004. The smaller earthquakes felt in the region were under the influence of the Sumatra-Andaman earthquake and many were recorded in the first part of the year,” explains N C Khaund of the Shillong-based Observatory.

He said a big earthquake was generally followed by a number of smaller earthquakes called after-shocks. But that year  part, the previous years had recorded lesser number of quakes, 16 in 2004, 14 in 2003 and 15 in 2003.

Seismologist Saurabh Barua of the North-East Institute of Science and Technology, however, said, “There is nothing to worry. Increase in the frequency of quakes is in fact a good signal as it only means the energy is being released gradually
and not kept held inside the earth.”  However, he cautioned that the region, lying in a high seismic risk belt, was vulnerable to big quakes and there is no co-relation between the increase in seismic activity and probability of a bigger quake.

“One cannot predict an earthquake,” Barua told PTI, underscoring the need for proper engineering practices and an adequate mitigation strategy.

The US-based GeoHazards International, in a report, had warned that a magnitude 8.3 earthquake striking Shillong might kill 60 times as many people as were killed during a similar size quake that hit in 1897.

The Shillong quake had killed 1,542 people.

The reason, it says, is the replacement of single-story bamboo homes with multistory, poorly constructed concrete-frame  structures, often on steep slopes, has made the population much more vulnerable.

"The damage due to this earthquake was near total destruction including immense flooding and fractures. The majority of brick-stone buildings in Shillong, Guwahati, Goalpara, Dhubri and Tura were destroyed and 1,542 people died. The loss was estimated around $30 million," Barua said.

He said between 1897 and 2001, the population has increased by 232%, while the simultaneous urbanisation rate was 603.

“Even if we assume that 50% of urbanisation is constrained by proper seismic designing, the probable severity of the destruction remains to be much higher than the earlier scenario,” he said.