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Why are earthquakes so frequent and often lately? What is the science behind the shaking?

In a recurring sequence of seismic events, northern India experienced intense tremors emanating from a powerful 5.6 magnitude earthquake in Nepal; this marked the second occasion in just three days that seismic rumbles have coursed through the northern regions of India due to a substantial quake in Nepal. The most recent two earthquakes struck Nepal on November 3, 2023, at 4:14 PM and November 6, 2023, at 4:33 PM and one earthquake struck the national capital Delhi on November 11, 2023, at 3:36 PM. These recurring seismic occurrences in the region have spurred questions regarding the causes behind this increased frequency, especially during November.

The Impact of Recent Earthquakes in Nepal

  • November 3, 2023: Initial Strike in Karnali Province

On November 3 at 18:02 UTC, Nepal experienced a 5.6 magnitude earthquake with an epicenter in Jajarkot of Karnali province, reaching a depth of 17.9 km. The tremors, felt across North India, resulted in 140 reported deaths and 140 injuries, according to the National Disaster Risk Reduction and Management Authority (NDRRMA) (ECHO, 04 Nov 2023).

  • November 6, 2023: Aftershock Raises Casualty Count

Days later, on November 6, another strong earthquake of 5.6 magnitude struck Nepal, leading to an increased impact. The Government’s Initial Rapid Assessment (IRA) revealed that the initial earthquake on November 3, with a magnitude of 6.4, caused widespread damage in the Jajarkot and Rukum Districts of Karnali Province. The total death toll reached 153, with 338 injuries. Over 4,000 homes were damaged, and around 1.3 million people were exposed, with approximately 0.25 million in need of humanitarian assistance within 72 hours (UNCT Nepal, 6 Nov 2023).

  • Ongoing Impact and Displacement

After the subsequent 6.4 magnitude earthquake, the situation continued to worsen. As of November 6, the NDRRMA reported a total of 157 fatalities, including 82 children, and 349 injuries. Jajarkot and Rukum West districts were heavily affected, witnessing over 10,000 people displaced. The damage assessment indicated that 17,740 houses were fully damaged, and 17,127 were partially damaged, painting a grim picture of the ongoing humanitarian crisis (Source: Save the Children).

Why are Earthquakes So Frequent? What Happens in November?

The surge in the frequency of powerful earthquakes, particularly in northern India, raises pertinent questions about the underlying geological factors that drive this phenomenon. It is essential to understand that earthquakes are a natural outcome of the Earth’s constantly shifting and evolving crust. The Earth’s outer layer, known as the crust, is a complex puzzle of tectonic plates continuously in motion. These plates interact in various ways – converging, diverging, colliding, or sliding past each other, resulting in the accumulation of stress and strain within the Earth’s crust. When this stress becomes too great, it is released, rupturing the crust and causing an earthquake.

The Role of Plate Boundaries

Most earthquakes manifest at plate boundaries, where tectonic plates engage with each other. These plate boundaries can be categorized into three primary types, each with its distinct characteristics:

  1. Convergent Boundaries: At convergent boundaries, two tectonic plates move toward each other and collide. The collision can lead to one plate being subducted or forced beneath the other, which, in turn, causes seismic activity.
  2. Divergent Boundaries: Divergent boundaries witness two plates moving away from each other. This movement fosters the creation of new crust and, concurrently, triggers earthquakes.
  3. Transform Boundaries: Transform boundaries are characterized by two plates sliding horizontally past each other. The ensuing friction and heat generated at these boundaries can incite earthquakes.

In addition to plate boundaries, earthquakes can also transpire within tectonic plates, albeit less frequently. These intraplate earthquakes are typically attributed to geological faults and fractures in the Earth’s crust.

Geographic Variability of Earthquakes

The frequency of earthquakes is unevenly distributed across the globe, with some regions being more susceptible to seismic activity than others. The Ring of Fire, encircling the Pacific Ocean, is a high seismic activity zone, hosting many of the world’s most significant volcanic eruptions and earthquakes.

Human Activities and Their Impact

Recent years have seen a concerning trend with the growing occurrence of human-induced earthquakes. Various human activities have been implicated as contributing factors:

  1. Fracking for Oil and Gas: Hydraulic fracturing, commonly called fracking, entails injecting high-pressure fluids into the Earth to extract natural gas and oil. This process can induce seismic events, especially in regions unaccustomed to such geological stress.
  2. Dam-Building: The construction of large dams can alter the stress on the Earth’s crust, occasionally leading to localized earthquakes.
  3. Groundwater Extraction: The depletion of underground water reservoirs can cause land subsidence, intensifying stress on the Earth’s crust and culminating in earthquakes.

The Earth’s Cooling and Volcanic Activity

Scientists have suggested that the Earth’s cooling may contribute to increased seismic activity. Cooling of the Earth’s interior results in the contraction of the crust, which, in turn, disrupts volcanic activity and, occasionally, incites earthquakes. This factor, though less comprehensively understood than tectonic plate movements, remains an active area of research.

The Indian Perspective: The Subduction of the Indian Plate

From an Indian vantage point, the region’s susceptibility to earthquakes is notably influenced by the gradual subduction of the Indian tectonic plate beneath the Eurasian plate. This ongoing convergence, progressing at a rate of 47mm per year, culminates in an energy accumulation, rendering the region more susceptible to high-magnitude earthquakes.

The November Connection: Seasonal Variation?

An intriguing facet that merits attention is the seasonality of earthquakes, particularly in Nepal. The proximity of the November 3 earthquake to subsequent seismic activity in early November prompts the question: Could there be a connection to November? Scientists are actively investigating this phenomenon, exploring whether these November earthquakes are a mere coincidence or if specific geological or atmospheric conditions contribute to this recurring trend.

Delhi-NCR: A Region Prone to Tremors

The frequency of earthquakes in the Delhi-National Capital Region (NCR) has long puzzled observers. This region experiences strong tremors every few months, and the recurrence of seismic activity in the Himalayan region exacerbates this phenomenon. The frequent seismic activity in Delhi-NCR can be attributed to its geographic location in a seismically active region.

The Seismic Zones in India

India is divided into seismic zones based on the level of earthquake risk, with Zone V being the most active and high-risk zone and Zone II representing the least active. The Delhi-NCR region is in Zone IV, categorized as “high risk.” While earthquakes of magnitude 4 to 4.5 are common in this region, the geographic location of Delhi, nestled in the Himalayan foothills, makes it prone to seismic activity.

Fault Lines in Delhi-NCR

The Delhi-NCR region harbours several fault lines, contributing to its seismic activity. Some of these fault lines include the Delhi-Haridwar Ridge, Mahendragarh-Dehradun Subsurface Fault, Moradabad Fault, Sohna Fault, Great Boundary Fault, Delhi-Sargodha Ridge, Yamuna River Lineament, Ganga River Lineament, and Jahazpur Thrust.

The Delhi-Aravalli Fold Belt

The Delhi-Aravalli range, known as the Aravalli-Delhi Fold Belt, was formed through tectonic activity. While these geological processes have largely subsided, the region may still experience minor earthquakes.

The surge in seismic activity, particularly during November, underscores the dynamic and ever-changing nature of our planet. While frequent tremors may occur, they are generally not a cause for immediate concern. It is imperative, however, to remain vigilant in regions prone to severe earthquakes, such as the Himalayan belt, and continue investing in earthquake-resistant infrastructure and early warning systems to mitigate the impact of these natural disasters. The Earth’s restlessness reminds us of our need for preparedness in the face of seismic uncertainty.

 

Read More: China’s Deflation Dilemma: A Setback in Economic Recovery

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