In recent news, a significant earthquake of 6.4 magnitude on the Richter Scale shook Assam along with other areas of Northeast India. As per the report from the National Centre for Seismology (NCS), the tremors are linked to the Kopili Fault zone near the Himalayan Frontal Thrust (HFT). NCS, under the Ministry of Earth Sciences, is the Government of India’s governing agency for monitoring earthquakes nationwide.
Understanding the Himalayan Frontal Thrust (HFT)
The HFT, also termed as the Main Frontal Thrust (MFT), is a geological breakage line along the Indian and Eurasian tectonic plates’ boundary.
The Kopili Fault Zone Exploration
Running across a length of 300 km and a width of 50 km, the Kopili fault zone extends from Manipur’s western part to the tri-junction of Bhutan, Arunachal Pradesh, and Assam. The area is significantly seismic, falling under Seismic Hazard zone V related to collision tectonics, which sees the Indian plate subduct beneath the Eurasian Plate.
Subduction refers to a geological process where a crustal plate is forced below the edge of another plate. Given its geographical location between the subduction and collision zones of the Himalayan belt and Sumatran belt, the North East is remarkably prone to earthquakes.
Fault and Its Impact
A fault is essentially a fracture where the blocks of crust on either side have moved relative to each other, parallel to the fracture. When an earthquake occurs, one side’s rock slips in respect to the other. The fault surface can be vertical, horizontal, or at some angle to the earth’s surface.
The Role of Tectonic Plates
A tectonic plate, also known as a lithospheric plate, is a broad, irregularly-shaped slab of solid rock, typically composed of both continental and oceanic lithosphere. Depending on which occupies the larger portion of the plate, a tectonic plate may be a continental or an oceanic plate.
Understanding Earthquakes
Simply put, an earthquake is the earth’s shaking. This natural event occurs due to the release of energy, creating waves that traverse in all directions. Vibrations known as seismic waves are produced by earthquakes, recorded on devices called seismographs.
The starting point of an earthquake beneath the earth’s surface is termed the hypocenter, and the area directly above it on the earth’s surface is named the epicenter.
Types of Earthquake
There are different types of earthquakes, including Fault Zones, Tectonic Earthquakes, Volcanic Earthquakes, and Human Induced Earthquakes.
Seismic Hazard Map of India
Due to the presence of tectonically active young fold mountains – the Himalayas, India is significantly affected by earthquakes. Based on scientific inputs about seismicity, past earthquakes, and the tectonic setup of the region, India has been divided into four seismic zones (II, III, IV, and V).
Previously, earthquake zones were split into five areas according to the severity of the earthquakes. The Bureau of Indian Standards (BIS), responsible for publishing the seismic hazard maps and codes, combined the first two zones to group the country into four seismic zones. These zones from II-V represent areas with minor damage earthquakes to the most seismically active regions, respectively.
Earthquake zone V is the most vulnerable, having experienced some of the country’s most powerful shocks. Earthquakes exceeding 7.0 magnitudes have occurred in these areas, resulting in intensities beyond IX.
