Y. Mallikarjun

HYDERABAD: Seismologists at the National Geophysical Research Institute (NGRI) here have embarked upon a study to decipher if there is any "global pattern" to the slightly-heightened seismic activity all over the world for the past few years.

"Suddenly we are seeing a spurt in seismic activity globally, although earhquakes are occurring in the expected regions," said R.K.Chadha, seismologist and deputy director, NGRI. "Nobody knows why. We are studying to find out if there are any global patterns," he told The Hindu on Tuesday.

He said that Tuesday's tremblor in the Hindukush region, though of 6.2 magnitude on the Richter scale had not caused devastation because it had a depth of 210 km.

The deeper the event, the wider would be the felt area (as in this morning's earthquake which was felt up to Delhi) and as a result might cause less damage. The Hindukush region was known for earthquakes of up to 300 km depth.

Such events normally occur in subduction zones (one plate going below another plate) like Java-Sumatra where the Indian plate was getting subducted below the Burmese plate.

Dr. Chadda said that shallow tremblors of less than 50 km depth and magnitude 8 or more were found to have caused extensive loss of lives and damage to buildings in the Himalayan belt and cited the examples of October 8, 2005 (Muzaffarabad), Arunachal Pradesh (1950), Bihar-Nepal border (1934), (Kangra-Himachal Pradesh 1905) and Shillong (1897).

However, complex tectonics seems to be taking place in the Hindukush region and that probably was the reason for deeper earthquakes .He said that the region was a sort of junction/knot between Indian, Eurasian and Arabian plates.