Definition:
Earthquake refers to sudden shaking of earth's crust caused by the release of energy in form of seismic waves.
Characteristics of earthquake:
1. Sudden shaking and vibrations due to seismic waves
2. Earthquakes last for few seconds to minutes. After shocks can be observed for prolonged period
Types of seismic waves -
1. Body waves or deep waves
i. P waves : Arrive first from focus, longitudinal waves (particle motion parallel to direction of wave propagation), travel faster than S waves, travel across solid, liquid and gas
ii. S waves : Arrive after P waves, transverse waves (particle motion perpendicular to wave propagation), travel only through solid
2. Surface waves
i. Rayleigh wave: Moves in an elliptical, rolling motion, both vertically and horizontally, in the direction of wave propagation
ii. Love wave: Moves purely horizontal and transverse, meaning the ground moves perpendicular to the direction of wave travel.
Causes of earthquake:
A. NATURAL
1. Techtonic plate movement -
a. Convergent boudary - one plate subduct beneath another plate causing volcanic and seismic activity e.g. 2011 Tohuku earthquake (9.0 magnitude)
b. Divergent boundary - plates move apart causing shallow earthquake
c. Transform boundary - Friction along side boudaries cause earthquake e.g. San Andreas fault
2. Volcanic activity - tremors of laval eruption shake up the crust e.g. around St. Helena volcanic eruption led to earthquakes in surrounding area
3. Magma movement - The magma influx and movement cases earthquake swarms (Reykjanes Peninsula)
4. Fault slippage - stress accumulation at faults cause sudden shaking e.g. Turkiye 2023 earthquake
B. HUMAN RELATED
1. Mining
2. Mine blasts
3. Dam failures
Measure of Earthquake -
1. Ritcher scale (1 to 9 units) measures magnitude of Earthquake
2. Mercaulli scale (0 to 10) measures intensity of earthquake
Impacts :
1. Structural Damage:
Buildings, bridges, and infrastructure collapses -
Example: The 2010 Haiti Earthquake (Mw 7.0) destroyed over 250,000 homes and killed over 200,000 people due to substandard buildings.
2. Loss of Life and Injury:
Falling debris, collapsing structures, and secondary effects like fires cause fatalities and injuries.
Example: The 2005 Kashmir Earthquake (Mw 7.6) in Pakistan killed over 80,000 people.
3. Tsunamis:
Underwater quakes can displace water, triggering tsunamis.
Example: The 2004 Indian Ocean Earthquake (Mw 9.1) caused a tsunami that killed over 230,000 people across 14 countries.
4. Landslides and Avalanches:
Shaking can destabilize slopes, causing landslides.
Example: The 2015 Nepal Earthquake (Mw 7.8) triggered landslides in the Himalayas, blocking roads and hindering rescue efforts.
5. Economic Impact:
Damage to infrastructure and disruption of businesses lead to significant economic losses.
Example: The 2011 Tohoku Earthquake caused $360 billion in damages, the costliest natural disaster in history.
Aftershocks:
Smaller quakes following the main event can cause further damage.
Example: Aftershocks of the 2010 Chile Earthquake
Best practices to tackle earthquake -
1. Building earthquake resistance houses e.g. Baiga houses in Rajasthan
2. Emergency planning
3. Mock drills for safety measures (drop and hide)
4. Insurance cover
Locations of Earthquake:
Case Study -
Japan located on two plate boundaries, experience earthquakes on regular basis. Developed systemic, coordinated multipronged strategy to tackle earthquake.
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