According to experts, earthquake swarming refers to a sequence of multiple earthquakes that can occur over days, weeks or months.
Around ten days ago and within two weeks of the devastating earthquake in Hindu Kush mountain range of Afghanistan, the Andaman and Nicobar Islands experienced a series of 14 earthquakes in a span of 24 hours between November 8 and November 9. The magnitude of the 14 quakes ranged from a maximum of 6 on Richter scale to the lowest of 4.7. Although the earthquakes did not cause damage in the sparsely populated Islands, scientists have categorised the multiple shocks as an 'earthquake swarm', tracing the cause back to the 2004 Indian Ocean earthquake that triggered a devastating tsunami.
According to experts, earthquake swarming refers to a sequence of multiple earthquakes that can occur over days, weeks or months. In this sequence, the magnitude of tremors typically grow in an ascending order and the one with the highest magnitude usually occurs in the middle of the sequence. The earthquakes experienced in Nicobar Islands too witnessed a similar sequence where the first quake was of 5.2 magnitude on the Richter scale and the seventh quake of 6 magnitude was the most intense.
"Earthquake swarms can be attributed either to an adjustment in the tectonic plates, which in is this case might have happened due to the collision between the major plates such as Indian Plate, Burma Plate and Sunda Plate. Swarms can also occur due to subsea volcanic eruptions. But it is not yet confirmed what caused the earthquakes earlier this month," said Vineet Kumar Gahalaut, director, National Centre for Seismology.
Historical data indicates that earthquake swarming is not rare. The last swarm of earthquakes in this region was experienced in September 2014 north of Nicobar Islands. In fact, following the massive earthquake in December 2004, a series of earthquakes were recorded beneath the Andaman Sea north-east of Nicobar Islands beginning January 2005.
Some experts were of the opinion that the earthquake swarm are aftershocks due to adjustments in faults caused by the 2004 quake. "Andaman and Nicobar Island region fall in the subduction zone -- vulnerable region -- and aftershocks are routinely felt. Since the rupture caused by the 2004 quake is about 1,200 km long it will take a few more years to adjusting between the tectonic plates," said KM Rao, scientist, Institute of Seismological Research, Gujarat.
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