Earthquakes happen due to the sudden release of energy in the Earth’s crust, creating seismic waves. This release of energy usually occurs because of movement along fault lines—cracks in the Earth’s crust where tectonic plates interact.

Causes of Earthquakes:

1. Tectonic Plate Movement (Most Common)
   • The Earth’s crust is divided into large pieces called tectonic plates.
   • These plates move slowly over the Earth’s mantle.
   • When they collide, pull apart, or slide past each other, stress builds up, and when it exceeds the rock’s strength, it causes a sudden rupture—resulting in an earthquake.
2. Volcanic Activity
   • Sometimes, earthquakes occur due to magma movement in volcanoes.
   • These volcanic earthquakes often precede an eruption.
3. Human Activities (Induced Seismicity)
   • Mining, dam construction, and drilling (such as fracking) can cause small earthquakes.
   • Nuclear tests can also trigger seismic activity.
4. Isostatic Rebound
   • When glaciers melt, the Earth’s crust adjusts, leading to earthquakes.
   • This is common in areas where ice sheets once covered the land.

Types of Faults That Cause Earthquakes

• Normal Faults → Due to plates pulling apart (divergent boundary).
• Reverse Faults (Thrust Faults) → Due to plates pushing together (convergent boundary).
• Strike-Slip Faults → When plates slide past each other (transform boundary, e.g., the San Andreas Fault).

Interesting Facts:

• The Ring of Fire (around the Pacific Ocean) is the most earthquake-prone area.
• The Richter Scale and Moment Magnitude Scale (Mw) measure earthquake strength.
• The largest earthquake ever recorded was in Chile (1960) with a magnitude of 9.5.