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Earthquakes: Key Concepts and Current Events

Earthquakes are critical geophysical phenomena that are fundamental to the UPSC CSE syllabus, encompassing disaster management and geography, including plate tectonics and seismic zones. They emphasize preparedness, mitigation strategies, and India’s seismic vulnerability.

Recent Events

• An earthquake with a magnitude of approximately 7 struck Tibet on January 7, resulting in around 100 fatalities and damage to about 1,000 houses.
• The epicenter was located 75 kilometers northeast of Mount Everest, near Nepal, yet there was no major damage reported in Nepal.
• This event was the most powerful in the area since the devastating April 2015 Nepal earthquake that caused approximately 10,000 deaths.

Causes and Mechanics of Earthquakes

• Earthquakes occur due to intense ground shaking caused by movements beneath the Earth's surface when two blocks of the Earth suddenly slip past one another, releasing stored 'elastic strain' energy as seismic waves.
• The Earth's crust is divided into tectonic plates, whose boundaries consist of faults. As these plates move, they may stick at the edges, and when they finally slip, an earthquake occurs.
• The location below the Earth's surface where an earthquake starts is called the hypocenter, while the point directly above it on the surface is the epicenter.

Prediction of Earthquakes

Currently, accurate prediction of earthquakes is not possible. It requires a precursory signal from within the Earth indicating a forthcoming major quake, which has yet to be detected by existing technology.

Seismic Activity in the Himalayan Zone

• The Himalayas were formed by the collision of the Eurasian and Indian tectonic plates, which continue to converge at a rate of 40-50 mm/year.
• The region has experienced at least five earthquakes of magnitude greater than 7 in the Hindu Kush since 1950, due to complex tectonic interactions.

Most Earthquake-Prone Countries

• Countries like China and Indonesia are highly prone to earthquakes, with Indonesia experiencing the most seismic events (2,212 earthquakes of magnitude 4 or more).
• According to NOAA, China has faced 186 major earthquakes between 1990 and 2024, followed by Indonesia with 166, and Iran with 109.

India's Seismic Vulnerability

• Ranked as the seventh most earthquake-prone country globally, India has experienced 58 significant earthquakes.
• Approximately 59% of India’s land area is susceptible to moderate or severe seismic events.

Theory of Plate Tectonics

The Earth's surface is divided into major and minor tectonic plates that move a few centimeters annually, leading to earthquakes through collisions and separations.

Types of Seismic Waves

• Body Waves: Travel through the Earth's interior and include Primary ('P') waves, which are compressional and can travel through solids, liquids, and gases, and Secondary ('S') waves, which are shear waves and do not travel through liquids or gases.
• Surface Waves: Confined near the Earth's surface, including Love waves (shear waves) and Rayleigh waves, which resemble ocean wave motions.

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