Earthquakes start at a point beneath the Earth's surface called the focus or hypocenter.

Here's a breakdown:

* Focus: The exact point where the rupture begins, releasing energy in the form of seismic waves. This is usually located within the Earth's crust or upper mantle.

* Epicenter: The point on the Earth's surface directly above the focus. This is the point where the earthquake's effects are usually strongest.

Earthquakes occur due to the movement of tectonic plates, which are massive pieces of the Earth's outer layer. When these plates collide, slide past each other, or pull apart, they create stress along their boundaries. This stress builds up over time until it exceeds the strength of the rocks, causing them to fracture and release energy in the form of seismic waves.

The location of the focus and epicenter can vary depending on the type of fault and the direction of plate movement.