Uttarakhand earthquake: What could have triggered 4.9-magnitude tremors?

A preliminary magnitude 4.9 earthquake struck Uttarakhand late on Tuesday, with tremors felt across parts of north India. Scientists say the region's complex Himalayan fault network is under scrutiny, but the trigger cannot be confirmed until the NCS completes its analysis.

In Short

• Preliminary 4.4 earthquake struck near Chamoli at 10:23 pm Tuesday night
• Tremors were felt across Uttarakhand, Himachal Pradesh, Punjab, Haryana and Delhi-NCR
• Epicentre was estimated about 22 km from Khadun Laga Gawali

An earthquake of preliminary magnitude 4.9 was reported in Uttarakhand on Tuesday night, with tremors felt across parts of Uttarakhand, Himachal Pradesh, Punjab, Haryana and Delhi-NCR.

According to the National Centre for Seismology, the quake occurred at 10:23 pm, with the estimated epicentre about 22 km from Khadun Laga Gawali in Chamoli district. The depth was 13 km below the surface.

Khadun Laga Gawali is located in the Gairsain area of Chamoli.

The NCS is India's nodal agency for monitoring earthquakes through a nationwide network of more than 170 seismic stations.

THE FAULT SYSTEM BEHIND UTTARAKHAND’S EARTHQUAKES

The location is particularly important because the Garhwal-Kumaon Himalaya sits in one of India’s most active seismic regions.

One of the most important tectonic structures here is the Main Central Thrust (MCT), a major geological boundary separating the Lesser Himalaya from the Higher Himalaya.

Researchers have found that many past earthquakes in Uttarakhand occurred close to the MCT.

But researchers will need some time to attribute Tuesday night’s earthquake to the MCT specifically once its precise depth, epicentre and focal mechanism are analysed.

The broader Himalayan system is driven by the continuing collision of the Indian and Eurasian tectonic plates.

The Main Himalayan Thrust (MHT) is the deeper fault system accommodating much of this convergence. Studies of the Garhwal-Kumaon region show that earthquakes frequently occur at shallow-to-intermediate depths associated with this complex fault network.

The region also contains several other major structures, including the Main Boundary Thrust, Himalayan Frontal Thrust, Moradabad Fault and Great Boundary Fault.

These structures segment the Uttarakhand Himalaya and influence how earthquake stress is distributed.

Uttarakhand has experienced damaging earthquakes in the past, including the 1991 Uttarkashi earthquake and the 1999 Chamoli earthquake.

For now, the 4.9 event should be treated as a moderate earthquake, and reports of tremors across northern India do not by themselves indicate that a larger earthquake is imminent.

Scientists will need the final NCS parameters before identifying which fault actually slipped.

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