What is an Earthquake and what causes them to happen?

 Earthquakes are caused by the movement of tectonic plates. The Earth's crust is made up of several large plates that float on the molten rock of the mantle. When two plates grind against each other, tremendous pressure can build up. Eventually, that pressure is released in the form of an earthquake. The point where the plates meet is called a fault line, and the movement of the plates along the fault line is what causes the ground to shake during an earthquake.

In addition to plate tectonics, earthquakes can also be caused by human activity such as the injection of fluids into the ground, the extraction of oil and gas, or the building of large dams. These activities can change the stress and pressure on the Earth's crust, leading to the movement of faults and the generation of earthquakes.

Another type of earthquake is volcano-tectonic earthquake. Those are caused by the movement of magma, fluids and gases in the subsurface of a volcano. They are typically associated with volcanic activity and can be a precursor to an eruption.

Earthquakes can also be caused by underground nuclear explosions, or even meteorite impacts. However, these types of earthquakes are extremely rare.

In summary, the main cause of earthquakes is the movement of tectonic plates, but other causes include human activity, volcanic activity, nuclear explosions, and meteorite impacts.