Earthquake tremors are caused by the disturbance deep down inside the uppermost layer of the earth called the ________.

- Most earthquakes occur along the edge of the oceanic and continental plates. The earth's crust (the outer layer of the planet) is made up of several pieces called plates.

- The plates under the oceans are called oceanic plates and the rest are continental plates. Earthquakes usually occur where two plates are running into each other or sliding past each other.