Model Answer
0 min readIntroduction
An earthquake is a sudden, violent shaking of the ground caused by the passage of seismic waves through Earth's rocks. These events are among the most destructive natural phenomena, resulting in significant loss of life and property damage. While often perceived as random, earthquakes are largely a consequence of Earth’s dynamic geological processes. Understanding the causes of earthquakes and their concentration in specific zones is crucial for hazard mitigation and preparedness. The majority of earthquakes occur along tectonic plate boundaries, a direct result of the forces at play within the Earth’s lithosphere.
Causes of Earthquakes
Earthquakes are primarily caused by the release of energy in the Earth’s lithosphere, creating seismic waves. These causes can be broadly categorized as:
1. Natural Causes
- Tectonic Plate Movement: This is the most significant cause. The Earth’s lithosphere is divided into several tectonic plates that are constantly moving. Interactions at plate boundaries – convergent, divergent, and transform – generate stress. When this stress exceeds the strength of the rocks, they rupture, causing earthquakes. Example: The 2011 Tohoku earthquake and tsunami in Japan were caused by subduction at the Pacific and North American plate boundary.
- Volcanic Activity: Volcanic eruptions can trigger earthquakes, though these are generally less powerful than those caused by tectonic movement. The movement of magma beneath the surface can cause stress and fracturing of rocks.
- Faulting: Existing faults (fractures in the Earth’s crust) can experience renewed movement, leading to earthquakes.
- Landslides & Rockfalls: Large landslides or rockfalls can generate small-magnitude earthquakes.
2. Human-Induced Causes (Induced Seismicity)
- Reservoir-Induced Seismicity (RIS): The weight of water in large reservoirs can increase pore pressure in underlying rocks, lubricating faults and triggering earthquakes. Example: The Koyna Dam earthquake in Maharashtra (1967) is a classic example of RIS.
- Deep-Well Injection: Injecting fluids (e.g., wastewater from oil and gas operations) deep underground can alter pore pressure and induce seismicity.
- Mining Activities: Collapse of mine workings or blasting can cause localized earthquakes.
- Nuclear Explosions: Underground nuclear tests can generate seismic waves that are detectable as earthquakes.
Why Seismic Belts are Confined to Plate Boundaries
Approximately 90% of the world’s earthquakes occur along plate boundaries. This is because the majority of the Earth’s internal stress is concentrated at these zones. The three main types of plate boundaries and their associated seismic activity are:
| Plate Boundary Type | Characteristics | Earthquake Characteristics |
|---|---|---|
| Convergent Boundaries | Plates collide; one may subduct under the other. | Deep-focus, high-magnitude earthquakes. Example: The ‘Ring of Fire’ around the Pacific Ocean. |
| Divergent Boundaries | Plates move apart; magma rises to create new crust. | Shallow-focus, low-to-moderate magnitude earthquakes. Example: Mid-Atlantic Ridge. |
| Transform Boundaries | Plates slide past each other horizontally. | Shallow-focus, moderate-to-high magnitude earthquakes. Example: San Andreas Fault in California. |
The friction and stress build-up along these boundaries, coupled with the sudden release of energy during fault rupture, are the primary drivers of seismic activity. Areas away from plate boundaries, within the plates themselves (intraplate earthquakes), are less common and often linked to ancient fault lines or induced seismicity.
Conclusion
Earthquakes are a complex geological phenomenon driven by both natural and anthropogenic factors. The concentration of seismic activity along plate boundaries is a direct consequence of plate tectonic theory and the immense stresses generated by the interaction of these plates. Understanding these causes and patterns is vital for developing effective earthquake prediction, early warning systems, and mitigation strategies to minimize the devastating impacts of these natural disasters. Continued research and monitoring are crucial for enhancing our preparedness and resilience.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.