08-Jan-2025

Earthquake in Tibet

Geography

Why in News ? 

  • A powerful earthquake struck the foothills of the Himalayas near one of Tibet's most sacred cities on January 7, 2025, claiming at least 126 lives and destroying hundreds of houses. 

What are Earthquakes? 

  • Earthquakes are the shaking of the earth caused by the release of energy in the Earth's crust, generating seismic waves. 
  • Seismic waves are recorded using instruments called seismographs. 
  • The starting point of an earthquake below the surface is the hypocenter, and the point directly above it on the surface is the epicenter. 

 Types and Causes of Earthquakes 

1. Fault Zone Earthquakes 

  1. Caused by movement along faults, which are breaks in the Earth's crust. 
  2. Friction between rock layers locks them until stress forces them to slide, releasing energy. 

Earthquakes in the faults 

2. Tectonic Earthquakes 

  1. The most common type. 
  2. Caused by the movement of tectonic plates (lithospheric plates) along convergent, divergent, or transform boundaries. 

3. Volcanic Earthquakes 

a. Occur in volcanic regions due to magma movement or stress changes in surrounding rocks. 

4. Human-Induced Earthquakes 

a. Result from activities like mining, reservoir construction, or explosions.

Earthquakes based on the depth of focus 

The earthquakes are divided into three zones: shallow, intermediate, and deep based on their depth which range between 0 – 700 km. 

  • Shallow earthquakes have a focus 0 – 70 km deep. 
  • Intermediate earthquakes have a focus 70 – 300 km deep. 
  • Deep earthquakes have a focus 300 – 700 km deep. (e.g., in the Wadati-Benioff zone, associated with subduction zones). 

Earthquake Distribution 

1. Circum-Pacific Belt ("Ring of Fire") 

a. Around the Pacific Ocean, with 81% of the world’s largest earthquakes. 

2. Alpide Belt 

a. Extends from Java to the Mediterranean, accounting for 17% of large earthquakes. 

3. Mid-Atlantic Ridge 

a. Along underwater divergent plate boundaries. 

Distribution of Earthquake 

Measuring Earthquakes 

  • Richter Scale: Measures the magnitude (energy released), ranging from 0-10. 
  • Mercalli Scale: Measures the intensity (visible damage), ranging from 1-12. 
  • Recorded using seismometers as zig-zag patterns. 

 Did You Know? 

Seismic Waves 

Seismic waves are vibrations caused by the release of energy during an earthquake. These waves travel through and along the Earth's surface, carrying the energy released from the earthquake's focus. There are two main types of seismic waves: body waves and surface waves. 

Body waves travel through the Earth's interior and are of two types, 

  1. P-Waves (Primary Waves): These are the fastest waves and the first to be detected by seismographs. P-waves can move through solids, liquids, and gases, compressing and expanding the material in their path, much like sound waves. 
  2. S-Waves (Secondary Waves): These are slower than P-waves and arrive later. They can only travel through solids and move in a shearing motion, causing greater ground displacement than P-waves. 
  • Surface waves, on the other hand, travel along the Earth's surface and are slower than body waves. However, they are the most destructive type of seismic wave as they cause significant ground movement and structural damage. Surface waves typically occur after body waves reach the surface and can produce rolling or shaking motions. 

Main Types of Seismic Waves