Have earthquakes really increased in India due to activation of Almora Fault? Experts weigh in

There has been an increase in the number of earthquakes in January to November, 2023 compared to the last three years, Union Minister of Earth Sciences Kiren Rijiju told the Lok Sabha on December 6, 2023. However, experts have questioned the government’s information on the causes of the increase in earthquakes. 

The minister’s submission to the Parliament read:

Data indicates increase in earthquake activity in the year 2023 and it was mainly attributed to the activation of the Almora fault in Western Nepal. 

The activation led to major earthquakes on January 24, 2023 (magnitude 5.8), October 3, 2023 (magnitude 6.2) and November 3, 2023 (magnitude 6.4), Rijiju said. These mainshocks, accompanied by subsequent aftershocks, have led to an increased frequency of earthquakes in the year 2023. However, the background seismicity remained unchanged during this period, he added.

Occasional moderate earthquakes and fluctuations in seismic activity are common in northern India and Nepal, the minister’s submission added. “Nepal and the neighbouring northern part of India, situated near the active faults of the Himalayan region, are highly seismically active areas prone to frequent earthquakes due to collision tectonics, where the Indian plate subducts beneath the Eurasian Plate,” it read.

Most media outlets carried the reply under the title “Almora fault becoming active”. However, experts disagree with the view. Down to Earth (DTE) talked to three different geologists, who unanimously rejected the idea of ​​the Almora Fault was active. Tectonic collisions are the only reason for earthquakes in the Himalayan region, they said. 

DTE spoke to Vineet Gehlot, senior scientist at the National Geophysical Research Institute and former director of the National Center for Seismology. Severe earthquakes don’t happen every year and when they do, many small earthquakes follow it, which are called aftershocks, he said. In 2023, two major earthquakes occurred — first in January and second in November. As a result, the number of earthquakes this year has increased. 

Gehlot said he has read the government submission. “The government has also stated the same thing. When the number of aftershock earthquakes is removed, the number of earthquakes that occur each year is not nearly the same. Unless there is a major earthquake, the numbers do not change much,” he said. 

However, bringing up the Almora fault activation seems to be a communication issue, according to Gehlot. There are significant differences between science communication, public communication, and political communication, he said. Science communication is founded on facts, but the public may interpret it differently and politicians may give it a different spin, he pointed out. 

Whenever an earthquake occurs, it is named. For example, the earthquake that occurred in Nepal was named the Gorkha earthquake, after the Gorkha district in Nepal. A Gorkha Fault also lies in the region, which is completely inactive. The earthquake occurred in the Main Himalayan Thrust under the Gorkha district, but was named the Gorkha earthquake, Gehlot stated.

A thrust fault is a break in the Earth’s crust. There are two thrusts in Kumaon, Uttarakhand: One is the South Almora Thrust and the other is the North Almora Thrust. This Almora Fault extends to western Nepal and is likely called by the same name in the neighbouring country as well. But the question is whether this earthquake happened on the Almora Fault, the expert pointed out.  

Geologists studying the tectonics of the Himalayas know that all the earthquakes that occur in the Himalayas, are due to a fault 15 to 20 kilometres below the mountain range called the Main Himalayan Thrust, Gehlot said. 

Both of the major earthquakes in 2023 occurred on the Main Himalayan Thrust. Its likely they were incorrectly attributed to the Almora Fault as it has been mapped. While it is not scientifically correct, the common people can accept the attribution. If scientific terminology is used, this earthquake occurred on the Main Himalayan Thrust, the geologist stated. 

In such a case, the government must clarify its response in Parliament. “Clarity is needed at two instances in the government’s response. Although nothing in the report is incorrect, it is difficult to communicate science to the general public, and many people misinterpret it,” Gehlot said.

On being asked if the Almora Fault was active, the geologist replied in negative. “Activation of a fault is a major event. None of the faults in the Himalayas — Main Boundary Thrust, North Almora Thrust or South Almora Thrust — are active. This must be clarified because it sends the wrong message to the public. People may believe that if a fault becomes active, a large earthquake will occur, but this is not the case. 

The Almora Thrust is not deep and does not reach the mantle, according to geologist MPS Bisht, former director of the Uttarakhand Space Application Centre (USEC). “While it is a thrust, it is also referred to as a fault by some. However, the possibility of an earthquake is negligible,” he said.

Describing the structure of the planet, Bisht said the top layer of Earth is called a crust, which is made of layered rocks. The next layer is the mantle, which is made of rocks in semi-molten form. The pressure in the mantle is very high and a lot of activities happen in the layer, which causes movements in the upper crust. 

The activities sometimes reach a boundary and where they end, they collide with the edge of another plate. 

According to Bisht, all of the energy in the mantle has been released in the Himalayan belt to date, with their epicentre remaining near the Main Boundary Thrust. “In such a case, if the government has mentioned the North or South Almora Thrust, I strongly disagree. To the best of my knowledge, there has never been an earthquake or energy release point on these thrusts,” he said.

The South and North Almora thrusts are not active, agreed SP Sati, geologist and associate professor of the Department of Basic Science, Veer Chandra Singh Garhwali Uttarakhand University of Horticulture and Forestry. “The Srinagar earthquake, which occurred many years ago, was said to have occurred on the Almora thrust, but scientists later clarified that it was not the case,” he said.