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Geography

Earthquakes – Notes for Exams

Earthquakes are sudden vibrations of the Earth’s surface caused by tectonic plate movements, volcanic activity, or human actions. They originate at a focus point and are measured by scales like Richter and Moment Magnitude. Major earthquake zones include the Pacific Ring of Fire. Preparedness and understanding earthquake effects are vital for safety.

What is an Earthquake?

  • An earthquake is a sudden shaking or vibration of the Earth’s surface caused by movement along faults or volcanic activity.
  • The energy released during an earthquake travels in the form of seismic waves.

Causes of Earthquakes

  1. Tectonic Plate Movements – Most earthquakes occur due to plate movements along fault lines.
  2. Volcanic Activity – Some earthquakes are caused by volcanic eruptions.
  3. Human ActivitiesMining, reservoir-induced seismicity (dams), and nuclear explosions can trigger earthquakes.

Parts of an Earthquake

  1. Focus (Hypocenter) – The point inside the Earth where the earthquake originates.
  2. Epicenter – The point on the surface directly above the focus.
  3. Seismic Waves – Energy waves that travel through the Earth, causing shaking.

Types of Seismic Waves

Wave TypeCharacteristicsSpeed
P-Waves (Primary Waves)Fastest, travel through solids & liquidsFastest
S-Waves (Secondary Waves)Only travel through solids, slower than P-wavesSlower
Surface WavesMost destructive, cause ground shakingSlowest

Measuring Earthquakes

  • Richter Scale – Measures magnitude (energy released) (1-10 scale).
  • Moment Magnitude Scale (Mw) – More accurate for large earthquakes.
  • Mercalli Scale – Measures intensity (damage caused) (I-XII scale).

Major Earthquake Zones of the World

  1. Pacific Ring of Fire – Most earthquake-prone zone (Japan, Indonesia, Chile).
  2. Himalayan Belt – India, Nepal, Pakistan experience frequent earthquakes.
  3. Mid-Atlantic Ridge – Submarine earthquakes in the Atlantic Ocean.

Major Earthquakes in History

EarthquakeYearMagnitudeCountry/RegionImpact
1906 San Francisco19067.8USAMassive destruction, fires
1960 Valdivia Earthquake19609.5ChileStrongest recorded earthquake
2004 Indian Ocean Tsunami20049.1IndonesiaDeadly tsunami
2011 Japan Earthquake20119.0JapanFukushima nuclear disaster
2015 Nepal Earthquake20157.8NepalHeavy destruction in Kathmandu

Earthquakes in India

  • India lies in Seismic Zones II to V, with Zone V being the most dangerous.
  • Major earthquake-prone regions:
    Himalayas (Uttarakhand, Himachal Pradesh, Sikkim, Assam, Arunachal Pradesh).
    Gujarat (Bhuj Earthquake 2001).
    Delhi NCR & Indo-Gangetic Plain.

Effects of Earthquakes

Ground Shaking – Causes building collapse.
Tsunamis – Underwater earthquakes generate massive waves.
Landslides – Mountainous areas experience rockfalls.
Liquefaction – Water-saturated soil loses strength, causing buildings to sink.


Earthquake Preparedness

Follow “Drop, Cover, and Hold” during an earthquake.
Use earthquake-resistant buildings in high-risk zones.
Early warning systems can save lives.
Evacuation plans & emergency kits are essential.


MCQs on Earthquakes

1. What is the point inside the Earth where an earthquake starts?

a) Epicenter
b) Hypocenter
c) Fault
d) Crust

Answer: b) Hypocenter


2. Which seismic wave travels fastest?

a) P-Wave
b) S-Wave
c) Surface Wave
d) Rayleigh Wave

Answer: a) P-Wave


3. The Richter scale measures what?

a) Damage caused
b) Earthquake intensity
c) Energy released
d) Depth of the earthquake

Answer: c) Energy released


4. Which region is most prone to earthquakes?

a) Amazon Rainforest
b) Pacific Ring of Fire
c) Sahara Desert
d) Siberia

Answer: b) Pacific Ring of Fire


5. What causes most earthquakes?

a) Tectonic plate movements
b) Wind storms
c) Volcanoes
d) Human activities

Answer: a) Tectonic plate movements


Short Answer Questions

1. What is an earthquake?

An earthquake is a sudden shaking of the Earth’s surface due to movement along faults or volcanic activity.


2. Name the types of seismic waves.

  1. P-Waves – Fastest, travel through solids & liquids.
  2. S-Waves – Slower, only travel through solids.
  3. Surface Waves – Most destructive.

3. What are the effects of earthquakes?

Earthquakes cause ground shaking, tsunamis, landslides, and liquefaction.


4. Which earthquake was the strongest ever recorded?

The 1960 Valdivia Earthquake (Chile) had a magnitude of 9.5, the highest recorded.


5. What safety measures should be taken during an earthquake?

  • Drop, Cover, and Hold technique.
  • Earthquake-resistant buildings in high-risk areas.
  • Evacuation plans & emergency kits.

Conclusion

Earthquakes are natural disasters that can cause widespread destruction. Understanding seismic zones, preparedness, and response is crucial for mitigating damage and saving lives.

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