Vulnerability of the Indian Himalayas and Nepal to Earthquakes

Late on Friday night, a seismic event with a magnitude of 6.4 originating in Nepal sent tremors through several areas in Bihar, as reported by officials. The death toll rose to 128. Preliminary information indicates that the seismic activity was felt in locations including Patna, Katihar, Motihari, and several districts along the Indo-Nepal border.

According to the National Centre for Seismology, the earthquake's epicenter was situated in Nepal, approximately 227 km to the north of Ayodhya and 331 km to the west-northwest of Kathmandu. The earthquake's effects extended to parts of northern India, including the National Capital Region. Notably, this marks the third occurrence of significant seismic activity in Nepal within a single month.

As per the experts, Nepal and the Himalayan region of India experience earthquakes daily, but the intensity used to be very low. News like Nepal comes only when the intensity of the Earthquake is too high on the Ritcher scale. Here we will talk about the terms related to earthquakes and how vulnerable Indian Himalayan rage is towards earthquakes.

What is an Earthquake?

An earthquake is the result of surface vibrations caused by internal disruptions within the Earth, which can be attributed to either natural or human activities.

The Earth's uppermost layer, approximately 100 km thick, is referred to as the lithosphere. It is fragmented into multiple plates that are in constant motion in diverse directions. Plate tectonics offers an explanation for various natural phenomena, including the formation of mountains, oceans, earthquakes, volcanoes, and changes in elevations from uplands to lowlands. This movement and deformation of plates define the field of plate tectonics.

Type of Earthquakes

• Minor earthquakes (Magnitude less than 3.0): Generally not felt by people and rarely cause any damage.
• Light earthquakes (Magnitude 3.0 to 3.9): Often felt but rarely cause significant damage.
• Moderate earthquakes (Magnitude 4.0 to 4.9): Noticeable shaking of indoor items, and rattling noises, but generally don't cause structural damage.
• Strong earthquakes (Magnitude 5.0 to 5.9): Can cause significant damage to buildings and structures.
• Major earthquakes (Magnitude 6.0 to 6.9): Can cause severe damage in populated areas.
• Great earthquakes (Magnitude 7.0 and higher): Can cause widespread and devastating damage over large areas.

What is Epicentre?

The area beneath the Earth's surface where an earthquake originates is referred to as the "focus," and the point on the Earth's surface directly above the focus is termed the "epicenter." The focus can be situated at different depths, including shallow (0-70 km), intermediate (70-300 km), and deep (300-700 km).

The Bureau of Indian Standards (BIS) has categorized India into four seismic zones based on its historical seismic activity. These zones, labeled II, III, IV, and V, represent varying degrees of seismic activity. Zone V is the most seismically active region, while Zone II experiences the least seismic activity.

What is the Richter scale?

The Richter scale, also known as the local magnitude scale (ML), is a logarithmic scale used to measure the magnitude of earthquakes. It was developed in 1935 by Charles F. Richter in collaboration with Beno Gutenberg. The Richter scale quantifies the energy released by an earthquake at its source, which is often referred to as its "magnitude."

The scale assigns a single number to an earthquake event, with higher numbers indicating a stronger earthquake. Each whole number increase on the Richter scale represents a tenfold increase in the amplitude of seismic waves and approximately 31.6 times more energy release. For example, an earthquake with a magnitude of 5.0 releases about 31.6 times more energy than one with a magnitude of 4.0.

It's important to note that while the Richter scale is well-known, seismologists and earthquake monitoring agencies now often use the moment magnitude scale (Mw), which is considered more accurate for measuring the size of larger earthquakes. However, the Richter scale is still widely used in popular media and discussions about earthquake magnitudes.

Moving Indian Plate

The Indian plate steadily advances northward at a pace of approximately 6.5 cm per year, entering into collision with the southward-moving Tibetan plate. This collision is the driving force behind the formation of the Himalayan mountain range.

This ongoing movement and the interaction of these plates, along with the presence of radioactive minerals, result in the accumulation of energy beneath the Earth's surface. This stored energy is subsequently discharged through areas of geological weakness, giving rise to seismic events, commonly known as earthquakes. The frequency of these earthquakes is an indication that the entire reservoir of energy has not been entirely released.

Nepal is an earthquake-prone zone primarily because of its unique geographical location and tectonic plate interactions. Several geological factors contribute to the region's seismic activity, they are:

• Himalayan Collision Zone: Nepal is situated in the Himalayan region, which was formed as a result of the ongoing collision between the Indian Plate and the Eurasian Plate. The Indian Plate is slowly but continuously moving northward, colliding with the Eurasian Plate. This tectonic collision results in immense pressure, causing stress to build up in the Earth's crust.

• Subduction Zone: To the south of Nepal, the Indian Plate is diving beneath the Eurasian Plate, creating a subduction zone. This process is known as subduction, and it further adds to the tectonic stress and increases the likelihood of earthquakes.

• Main Boundary Thrust: The Main Himalayan Thrust (MHT) fault is a major fault line that runs beneath the Himalayan region, including Nepal. It is the primary fault responsible for generating powerful earthquakes in the region. When the accumulated stress along the fault is released, it causes the Earth's crust to move abruptly, resulting in seismic events.

• Aftershocks and Fault Systems: Following a significant earthquake, there are often aftershocks as the Earth's crust continues to adjust. Nepal is crisscrossed by various fault systems, and the movement along these faults can trigger aftershocks and even additional earthquakes.

• Rugged Terrain: Nepal's rugged and mountainous terrain further complicates the seismic activity. The steep slopes and fragile rock structures in the Himalayas can lead to landslides and secondary hazards following an earthquake.

• Plate Boundary Complexities: The tectonic interactions in this region are complex due to the presence of multiple fault lines and the convergence of various tectonic plates. This complexity increases the likelihood of seismic events.

• Historical Seismic Activity: Nepal has a history of powerful earthquakes, with records of significant seismic events dating back centuries. This history of earthquakes in the region is indicative of the ongoing tectonic activity.

Due to these geological factors, Nepal remains highly susceptible to earthquakes and experiences periodic seismic events. The 2015 earthquake, with a magnitude of 7.8, was a stark reminder of the region's vulnerability to such natural disasters. Both residents and visitors to the area need to be prepared for seismic activity and follow safety guidelines to minimize the impact of earthquakes.

What does the Expert says?

Professor Dhruvsen Singh, Head Department of Geology, University of Lucknow and Director, Institute of Hydrocarbon Energy and Georesources, said that the earthquake is caused by tectonic activities and the Himalayas are full of tectonically induced features such as fold, faults, and thrust. The major thrusts separate one part of the Himalayas from the other. The Main Central thrust separates the Higher Himalaya from the middle Himalaya, the Main Boundary thrust separates the Middle Himalaya from the Shiwaliks ( Outer Himalaya) and the Himalayan Frontal thrust separates Shivalik from the Ganga Plain. It has been observed that these thrusts have been activated in recent times causing earthquakes. So all those parts of India which are located in the Himalaya and northern part of Ganga Plain are more prone to earthquakes.