What causes earthquakes?
Plate Tectonics Theory The plate tectonics theory is a starting point for understanding the forces within the Earth that cause earthquakes. Plates are thick slabs of rock that make up the outermost 100 kilometers or so of the Earth.( Figure 8) Geologists use the term tectonics to describe deformation of the Earth’s crust, the forces producing such deformation, and the geologic and structural features that result. Earthquakes occur only in the outer, brittle portions of these plates, where temperatures in the rock are relatively low. Deep in the Earth’s interior, convection of the rocks, caused by temperature variations in the Earth, induces stresses that result in movement of the overlying plates ( Figure 9. ). The rates of plate movements range from about 2 to 12 centimeters per year and can now be measured by precise surveying techniques. The stresses from convection can also deform the brittle portions of overlying plates, thereby Storing tremendous energy within the plates. If the
Earthquakes are caused by the slow deformation of the outer, brittle portions of “tectonic plates”, the earth’s outermost layer of crust and upper mantle. Due to the heating and cooling of the rock below these plates, the resulting convection causes the adjacently overlying plates to move, and, under great stress, deform. The rates of plate movements range from about 2 to 12 centimeters per year. Sometimes, tremendous energy can build up within a single, or between neighbouring plates. If the accumulated stress exceeds the strength of the rocks making up these brittle zones, the rocks can break suddenly, releasing the stored energy as an earthquake.
