Large earthquakes imminent in the Himalayas

A new study has reconfirmed the possibility that large earthquakes could be imminent in the Himalayas. While high levels of strain are getting constantly accumulated along the Main Himalayan Thrust region, only a fraction of it is getting released through small earthquakes of magnitudes less than five on the Richter scale.

The study is based on the data collected from 70 continuous and three episodic GPS stations in different parts of the country over a period of two decades from 1996 to 2015. Out of the 73 GPS stations, 43 were located all along the seismically active northern (Himalayas) and eastern (Indo-Burmese and Andaman Arc) boundaries of the Indian tectonic plate. 

In a study published recently in the journal Scientific Reports, researchers say, “Inverse modelling of India-fixed GPS rates of Himalayan sites (three to 20 mm per year) from Ladakh in the west to Arunachal Pradesh in the east give the varying slip of 16-20 mm per year along the MHT at a depth of 15 to 20 km with a width of about 70-100 km from the Frontal Himalayan Thrust (FHT) i.e. the foothills of Himalayas.” 

“This indicates high strain accumulation along the MHT, a fraction of it being released by earthquakes of a magnitude of less than 5.0. Thus, the elastic strain accumulated over a long period of time would be released by a slip along the locked MHT causing large Himalayan earthquakes in the future,” researchers say.                            

The study is also significant as it has come up with a new angular velocity for the Indian plate. It has found that the plate had three percent higher angular velocity than all previous estimates. This indicates more rapid variations in the rate and direction of the movement along the boundaries of the plate. The finding would be of great use to researchers globally as it is expected to help determine the crustal motion within the Indian plate and its boundaries more accurately up to millimetre precision. 

Speaking to India Science Wire, senior principal scientist at CSIR’s Bengaluru-based Fourth Paradigm Institute (CSIR-4PI) and the leader of the team, Dr Sridevi Jade says the study is data intensive and unique as it is for the first time that the angular velocity of the Indian tectonic plate is estimated using as many as 30 continuous GPS sites within the plate which include, for the first time, sites from both the western and eastern regions. 

The study has ruled out any segmentation of the Indian plate. “No doubt, there have been earthquakes within the Indian plate, notable being the 2001 Bhuj and 1993 Latur earthquakes. But, they were due to localised regional deformations along active faults in these regions. Strain rates estimated for the different parts of the plate interior clearly indicate that there is low or no deformation at all in the plate interior and the plate motion is best described with a single angular velocity,” Dr Jade says. 

The team has suggested a detailed investigation of the area around Thiruvananthapuram and Pune after they found that these two isolated GPS stations are moving at a rate of 3 mm per year. Calling for the setting up of dense networks of GPS stations in the two regions, the researchers noted that the movement maybe due to some localised active deformation. “There is a need to delineate the regional deformations in the two regions,” says Dr Jade. 

Thiruvananthapuram and its neighbourhood that comes within what is called Achankovil Shear Zone which covers a 130-km-long swathe of land cutting across Kerala and Tamil Nadu, while Pune falls in the Panvel Flexure zone on the western continental margin of the Indian plate. 

The research team included T.S. Shrungeshwara of CSIR-4PI; Dr Kireet Kumar of G.B. Pant National Institute of Himalayan Environment and Sustainable Development, Almora; Dr Pallabee Chaudhury and Dr Rakesh K. Dumka of Institute of Seismological Research, Gandhinagar; and Dr Harish Bhu of M.L. Sukhadia University, Udaipur. The study was funded by CSIR under its Advanced Research in Engineering & Earth Sciences (ARiEES) project and the Ministry of Earth Sciences. (India Science News)