The three main types of earthquakes are transform, convergent and divergent. Transform fault earthquakes are sometimes called strike-slip earthquakes because they occur when tectonic plates slide against one another. Convergent earthquakes occur when land masses are thrust toward each other, while divergent earthquakes occur when plates are moving apart.
The cause or source zone is sometimes used as a way to categorize earthquakes. When earthquakes are categorized by cause, types include tectonic earthquakes, volcanic earthquakes and explosive earthquakes. Explosive earthquakes are often man-made, and the two terms may be used interchangeably. When source zone is used to categorize earthquakes, the primary earthquake types are shallow-fault, deep zone and crustal earthquakes.