E-Paper
Tremors in Andaman & Nicobar: 25 seismic events recorded in 2 days — Analysis
There were 25 seismic events of magnitude range between 3.8 and 5 reported in the region in the past two days
In the wake of a dozen seismic events reported in the Andaman and Nicobar Region on Monday and Tuesday, a depth distribution analysis of the earthquakes has suggested that the events were mostly concentrated at mid-crustal level and along back-arc, the National Center for Seismology (NCS) said.
There were 25 seismic events of magnitude range between 3.8 and 5 reported in the region in the past two days, and the NCS analysis found the epicentre locations of these earthquakes between the West Andaman Fault and Andaman Spreading Ridge.
“The continuous occurrences of earthquakes in the magnitude range varying between M:3.8 and M:5.0 suggest the release of accumulated seismic strain due to the perturbation of the stress level in the areas of the subducting Indian plate and its surroundings,” the analysis said.
The back-arc basin in the Andaman Sea region has experienced several (seismic) swarms as well aftershocks activity in the past five decades, with varying depth and magnitude. “The present earthquake activity is not unusual and witnessed such activity in the past,” the analysis said. Three major phases of swarm activities during 1983-1984, 1993 and 2005, and major aftershocks activity of 2009-2010 has been reported.
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The 1983-1984 event consisted of about 50 seismic events (3.5-5.5 M). During December 1983 to March 1984, the swarms clustered along the eastern side of the Alcock Rise on the NE-SW oriented Andaman Spreading Ridge. The 1993 swarm included only about 35 seismic events (3.5-5 M), which were clustered at the southwest segment of the central Andaman Spreading Ridge. During January 26, 2005 to February 2, 2005, the most intensive aggregate earthquake swarm called Nicobar cluster consisted of about 400 events of 3.9-5.9 M occurred in the Andaman Sea, the back-arc region of Sumatra- Andaman subduction zone, between the Car-Nicobar and Great Nicobar Islands.
“There were also some major aftershocks activities during the period from June-November 2005, August 2009 to June 2010 at Andaman Trench and Andaman spreading Ridge, indicating the continuous release of seismic strain in the region from time to time,” the report said.
The Andaman & Nicobar represents a complex topography comprising of a volcanic arc system, back-arc spreading ridge, several sea-mounts and faults. The region has been placed in Zone-V, the highest level of seismic hazard potential, according to the seismic zonation map of India by Bureau of Indian Standards published in 2016.
“These are major seismic events that are recorded from time to time because the Andaman & Nicobar region is in the highest seismic hazard zone. They are not unusual. Earthquakes cannot be predicted so we cannot say immediately if there will be more such events,” said a senior official of NCS.
