Earthquake: Causes, Types, Effects, Distribution, and Management – A Comprehensive Study

Introduction to Earthquakes

An earthquake is defined as a sudden shaking or vibration of the Earth’s surface brought on by the lithosphere’s accumulated stress. The ground shakes as a result of the seismic waves produced by this stress release radiating outward. Earthquakes can range in intensity from small, human-inaudible tremors to massive, destructive events.

Definition

An earthquake is the term used to describe the earth’s vibration caused by the quick release of energy from the crust or upper mantle.

Key Terms

Focus (Hypocenter): The focus, also known as the hypocenter, is the location on Earth where the earthquake begins.

Epicenter: The location directly above the focus on Earth’s surface is known as the epicentre.

Seismic Waves: Seismic waves are energy waves produced when rock within the Earth suddenly fractures.

Causes of Earthquakes

1. Tectonic Movements (Most Common Cause)

• There are large and small tectonic plates that make up the Earth’s crust.• Convection currents in the mantle cause plates to shift, forming plate boundaries where the majority of earthquakes take place.

• Types of Plate Boundaries:

o Convergent (collision and subduction zones): the Japan Trench and the Himalayas are two examples.

o Divergent (spreading boundaries): Mid-Atlantic Ridge, for instance.

o Transformation (Sliding Boundaries): San Andreas Fault, USA, as an example.

2. Volcanic Activity

Earthquakes may be caused by magma movement beneath volcanic regions. Mount St. Helens in the United States and Krakatoa in Indonesia are two examples.

3. Faulting and Folding

Earthquakes are caused by abrupt displacement along fault lines. The North Anatolian Fault in Turkey is one example.

4. Induced Seismicity (Human Activities)

Large reservoirs and dams put more strain on the underlying rocks, and deep drilling and mining explosions also produce tremors.  Koyna Dam in Maharashtra is a prime example of reservoir-induced seismicity (RIS) in India.

Types of Earthquakes

1. Tectonic Earthquakes

More than 90% of earthquakes worldwide are caused by movement along plate boundaries. • For instance, the 2015 Nepal Earthquake (magnitude 7.8).

2. Volcanic Earthquakes

Linked to volcanic eruptions; for instance, the 2010 Eyjafjallajökull eruption in Iceland.

3. Collapse Earthquakes

Local and low intensity; caused by cave-ins in karst landscapes or underground mines.

4. Explosion Earthquakes

• Initiated by chemical or nuclear explosions.
  • The nuclear tests conducted by North Korea are one example.

5. Reservoir-Induced Seismicity

• Large reservoirs’ water pressure stresses faults.
  • Koyna Earthquake, 1967 (magnitude 6.3) is one example.

Seismic Waves – Types and Characteristics

1. Body Waves

Travel through the Earth’s interior.

• Primary Waves (P-Waves)

• The quickest, passing through gases, liquids, and solids.
• Compressional waves, also known as push-pull motion.

• Secondary Waves (S-Waves)

o Slower and limited to solids.
o Shear waves (motion from side to side).

2. Surface Waves

Cause the most harm as you move across the surface of the Earth.

• Love Waves: Shear motion in a horizontal direction.
  • Rayleigh Waves: Circular, rolling motion akin to water waves.

Measurement and Scales

1. Magnitude – Energy Released

• Richter Scale (obsolete for large quakes).
• Moment Magnitude Scale (Mw) – Currently used globally.
• Example: Tōhoku Earthquake, Japan (2011) – 9.1 Mw.

2. Intensity – Damage Caused

• Modified Mercalli Scale (MMI) – I to XII (Qualitative).

Global Distribution of Earthquakes

1. Circum-Pacific Belt (“Ring of Fire”)

• Accounts for ~81% of global earthquakes.
• Covers Japan, Indonesia, Chile, Mexico, New Zealand, etc.

2. Alpide Belt

• Extends from Mediterranean region to the Himalayas.
• Accounts for ~17% of global earthquakes.

3. Mid-Atlantic Ridge

• Seismic activity along divergent boundary.

Earthquake-Prone Zones in India

Seismic Zoning in India

Key Facts

• 59% of Indian landmass is vulnerable to earthquakes.
• Historically destructive earthquakes:
  • 1897 Shillong Earthquake (8.1 Mw)
  • 1934 Bihar-Nepal Earthquake (8.0 Mw)
  • 2001 Bhuj Earthquake (7.7 Mw)

Effects of Earthquakes

1. Primary Effects

• Ground shaking.
• Surface rupture.

2. Secondary Effects

• Tsunamis: Submarine earthquakes (Japan, 2011 – 9.1 Mw).
• Landslides: Nepal, 2015.
• Soil Liquefaction: Ground behaves like liquid – Niigata, Japan (1964).

3. Long-Term Impacts

• Loss of infrastructure.
• Economic slowdown.
• Population displacement.
• Increased vulnerability to diseases.

Earthquake Preparedness and Management

1. Structural Mitigation

• Earthquake-resistant building codes.
• Retrofitting older buildings.
• Use of shock absorbers and base isolation techniques.

2. Non-Structural Mitigation

• Seismic hazard mapping.
• Early warning systems (Japan’s advanced EWS).
• Public awareness campaigns (school and community programs).

3. Disaster Response and Recovery

• National and State Disaster Response Forces (NDRF, SDRF).
• Post-disaster damage assessment.
• Relief distribution and rehabilitation.

Recent Earthquake Trends – Facts & Figures

Indian Scenario

• Recent Earthquakes in India (2010-2024):
  • 2011 Sikkim Earthquake – 6.9 Mw
  • 2015 Nepal Earthquake (Impact on India) – 7.8 Mw
  • 2023 Jammu & Kashmir Tremor – 5.8 Mw

Recent Earthquake Trends – Facts & Figures (2025)

Global Earthquake Statistics (January 1 – March 6, 2025)

• Total Recorded Earthquakes: Approximately 2,549 events of magnitude 4.0 and above.
• Significant Earthquakes (Magnitude ≥ 6.0): 11 events.
• Largest Recorded Earthquake: Magnitude 7.6 near the Swan Islands, offshore of Honduras, on February 8, 2025. This event caused structural damages and power outages in parts of Honduras and Belize.

Notable Earthquakes in 2025

1. Tibet Autonomous Region, China – February 3, 2025
   • Magnitude: 7.1
   • Depth: 10 km
   • Impact: Resulted in 126 to 400 fatalities.

1. North Hollywood, Los Angeles, USA – March 2, 2025
   • Magnitude: 3.9
   • Depth: Shallow focus
   • Impact: Felt widely across Los Angeles, including areas like Pasadena and Long Beach. Occurred shortly after the 2025 Academy Awards, with tremors captured during a Vanity Fair afterparty livestream. No significant damage or injuries reported.

1. Queensland, Australia – March 1, 2025
   • Magnitude: 4.4
   • Depth: 10 km
   • Impact: Felt across regions including Townsville, Cairns, Mackay, and the Sunshine Coast. Described by residents as resembling a “bomb” explosion. Led to power outages affecting over 4,200 residents, with electricity restored within 20 minutes. No significant structural damages reported.

1. Davao del Sur, Philippines – March 4, 2025
   • Magnitude: 5.0
   • Depth: 16.6 km
   • Impact: Ten students hospitalized due to injuries. Power outages reported in various areas of Davao del Sur.

1. Ayeyarwady Region, Myanmar – March 4, 2025
   • Magnitude: 5.1
   • Depth: 10 km
   • Impact: Several houses, a monastery, and a pagoda collapsed. Additional religious buildings sustained damage in the epicentral area.

Comparative Analysis (2015–2025)

*Data for 2025 is up to March 6.

Conclusion

One of the most destructive and unpredictable natural disasters, earthquakes have the power to alter landscapes, upend economies, and put lives in danger. Effective disaster preparedness and mitigation strategies require an understanding of their causes, mechanisms, and global distribution. Earthquakes do not respect national boundaries and can occur in both tectonically active and relatively stable regions, as demonstrated by the recent seismic events of 2025, which included the 7.6 magnitude earthquake near Honduras and the tremors in Myanmar, the Philippines, and Los Angeles.

Human settlements are more vulnerable to seismic events due to the growing population density in seismically active areas, as well as the rapid development of infrastructure and urbanisation. This emphasises how crucial it is to incorporate public awareness campaigns, early warning systems, resilient infrastructure, and advanced building codes into national disaster management frameworks.

Our knowledge of seismic processes is being improved by scientific developments like enhanced seismographic networks, satellite monitoring, and machine learning-based prediction models. However, because earthquakes are inherently unpredictable, the first line of defence against these devastating occurrences will always be strong preparation and community resilience.

In the end, lowering earthquake risks and safeguarding lives and livelihoods in the years to come depend on developing a culture of disaster preparedness, enhancing international collaboration in seismic research, and encouraging sustainable development in seismically vulnerable areas.