Earthquakes are caused by the sudden release of energy in the Earth’s crust, resulting in seismic waves that shake the ground. The primary cause of earthquakes is the movement and interaction of tectonic plates, which make up the Earth’s outer shell. There are three main types of plate boundaries where earthquakes commonly occur:
- Convergent Boundaries: When two tectonic plates collide or move towards each other, it creates a convergent boundary. Depending on the types of plates involved, these boundaries can lead to subduction zones or collision zones. Subduction zones occur when one plate is forced beneath another into the Earth’s mantle, causing intense pressure and friction. Collision zones occur when two continental plates collide, resulting in the formation of mountain ranges. The intense forces at convergent boundaries can cause significant earthquakes.
- Divergent Boundaries: At divergent boundaries, tectonic plates move away from each other. This process occurs mainly along mid-ocean ridges, where new crust is formed as molten material rises from the Earth’s mantle. The separation of plates and the movement of magma can lead to earthquakes, although they are generally less powerful than those at convergent boundaries.
- Transform Boundaries: Transform boundaries occur when two tectonic plates slide past each other horizontally. As the plates grind against each other, friction builds up, preventing smooth movement. When the accumulated stress overcomes the friction, sudden slippage occurs, releasing a significant amount of energy. Transform boundaries, such as the San Andreas Fault in California, are known for producing powerful earthquakes.
It’s important to note that earthquakes can also occur within tectonic plates, away from plate boundaries. These are referred to as intraplate earthquakes. Intraplate earthquakes can be caused by the buildup and release of stress due to geological factors like ancient faults, crustal deformation, or volcanic activity.
The released energy during an earthquake propagates as seismic waves through the Earth, shaking the ground and causing the characteristic tremors. The severity of an earthquake is measured on the Richter scale or the moment magnitude scale, which quantifies the amount of energy released.
While tectonic activity is the primary cause of earthquakes, other factors such as volcanic eruptions, landslides, and human activities (such as underground mining or reservoir-induced seismicity) can also trigger seismic events, although they are relatively less common.