Earthquake occurs when the tectonic plates situated inside the Earth's crust start colliding with each other.

How Earthquakes Occur
Earthquakes are caused by the sudden release of energy in the Earth's crust that creates seismic waves. This release of energy can be triggered by a variety of natural processes.

Tectonic Plate Movements
- The primary cause of earthquakes is the movement of tectonic plates. These massive slabs of rock float on the semi-fluid mantle beneath them and are constantly shifting.
- When two plates grind against each other, they can become locked due to friction. As stress builds up, eventually, the rocks break, releasing stored energy in the form of seismic waves.

Fault Lines
- Fault lines are cracks in the Earth's crust where tectonic plates meet. When the stress along these fault lines becomes too great, the rocks on either side of the fault slip, causing an earthquake.
- The point on the fault line where the earthquake originates is called the focus, while the point directly above it on the Earth's surface is called the epicenter.

Types of Faults
- There are three main types of faults: normal faults, reverse faults, and strike-slip faults. Each type of fault can produce different types of seismic waves and result in different types of earthquakes.

Seismic Waves
- When an earthquake occurs, it generates different types of seismic waves, including P-waves, S-waves, and surface waves.
- These waves radiate out from the focus of the earthquake, shaking the ground and causing the destruction we associate with earthquakes.
In conclusion, earthquakes are a natural phenomenon caused by the movement of tectonic plates and the release of energy along fault lines in the Earth's crust. Understanding the causes and effects of earthquakes is crucial for predicting and preparing for these potentially devastating events.