What Causes Earthquakes

In plate tectonics and the study of earthquakes, the first question that most people ask is what causes earthquakes.

We have already discussed tectonic plates movements and different plate boundaries. We also mentioned that convergent boundaries, divergent boundaries and transform boundaries can create fault zones and earthquakes are caused by faulting. San Andreas Fault in Southern California is a classic example of a fault zone where earthquakes often occur. Motion of tectonic plates can set off earthquakes in areas that contain faults.

Theories of what causes earthquakes

In the past, people know about earthquakes but they did not know what caused earthquakes. In 1890s, after the Great Japanese Earthquake of 1891 called the Mino-Owari earthquake, Japanese geologist Bunjiro Koto proposed that earthquakes were caused by faults, providing convincing evidence that earthquakes were triggered by the fracturing of the earth's crust. Bunjiro Koto was the first to link the relationship between earthquakes and faulting. Bunjiro Koto was later known in Japan as the Father of Geology and Petrology in Japan.

In the US, after the Great San Francisco earthquake of 1906, Professor of Geology at Johns Hopkins University Henry Fielding Reid proposed the elastic rebound theory. Elastic rebound theory further stresses the relationship between earthquakes and faulting and is now commonly used in plate tectonics. For ore details of Professor Henry Reid's Elastic Rebound Theory, see Reid, H.F., The Mechanics of the Earthquake, The California Earthquake of April 18, 1906, Report of the State Investigation Commission, Vol.2, Carnegie Institution of Washington, Washington, D.C. 1910 (see especially pages 16-28).