An earthquake occurs when there is a sudden release of energy in the Earth's crust, causing the ground to shake. This happens due to the movement of tectonic plates, which are massive slabs of rock that make up the Earth's surface.
- Tectonic Plate Movement:
- The Earth's crust is divided into large plates that float on the semi-fluid mantle beneath.
- These plates are constantly moving, but they often get stuck at their edges due to friction.
- When the stress on the edge overcomes the friction, the plates slip, releasing stored energy.
- Faults and Energy Release:
- Faults are fractures in the Earth's crust where movement occurs.
- When plates move along these faults, energy is released as seismic waves, causing the ground to shake.
- Common types of faults include strike-slip, normal, and reverse faults, depending on the direction of movement.
- Focus and Epicenter:
- The point inside the Earth where the earthquake originates is called the focus (or hypocenter).
- The point directly above the focus on the Earth's surface is the epicenter, where the shaking is usually strongest.
- Seismic Waves:
- The energy released travels as seismic waves, which are categorized as:
- Primary (P) waves: Fast-moving, compressional waves that travel through solids and liquids.
- Secondary (S) waves: Slower, shear waves that travel only through solids.
- Surface waves: Travel along the Earth's surface, causing most of the damage during an earthquake.
- The energy released travels as seismic waves, which are categorized as:
- Causes of Earthquakes:
- Natural Causes:
- Tectonic plate movement (most common).
- Volcanic activity, where magma movement causes tremors.
- Landslides or collapsing caves (less common).
- Human-Induced Causes:
- Mining, fracking, or reservoir-induced seismicity (e.g., from filling large dams).
- Nuclear explosions or large-scale construction activities.
- Natural Causes:
- Measuring Earthquakes:
- Earthquakes are measured using:
- Magnitude: The energy released, measured on the Richter scale or moment magnitude scale (e.g., 3.0 = minor, 7.0+ = major).
- Intensity: The impact on people and structures, measured by scales like the Modified Mercalli Intensity Scale.
- Earthquakes are measured using:
Earthquakes are more frequent along plate boundaries, such as:
- The Pacific Ring of Fire (around the Pacific Ocean).
- The Himalayan belt (collision of Indian and Eurasian plates).
- Mid-ocean ridges and transform faults.
Effects of Earthquakes:
- Ground shaking, which can damage buildings, bridges, and infrastructure.
- Surface rupture, where the ground splits along a fault.
- Secondary effects like tsunamis, landslides, or liquefaction (when soil behaves like a liquid).
