At spreading zones , molten rock rises, pushing two plates apart and adding new material at their edges. Most spreading zones are found in oceans. Spreading zones usually have earthquakes at shallow depths. Subduction zones are found where one plate overrides, or slips over , another, pushing it downward into the mantle where it melts. Deep-ocean trenches, shallow to deep earthquakes, and mountain ranges containing active volcanoes, characterize subduction zones.
Earthquakes can also occur within plates.
Although less than 10 percent of all earthquakes occur within plate interiors. As plates continue to move and plate boundaries change over long periods of time, weakened boundary regions become part of the interiors of the plates. These zones of weakness within the continents can cause earthquakes in response to stresses that originate at the edges of the plate or in the deeper crust. The point beneath the Earth's surface where the rocks actually break and move is called the focus of the earthquake. The focus is the underground point of origin of an earthquake.