Earthquakes and faults

The causes of earthquakes have interested man since antiquity. As was mentioned in section 1.1, various ideas have been proposed from the time of the ancient Greek natural philosophers to our days. During the 19th century systematic field studies after earthquakes were started and the first attempts to relate them to tectonic processes were made by Mallet (Naples, Italy, 1857), Koto (Neo, Japan, 1891), and Oldham (Assan, India, 1897) among others. With the increase in number of field observations and in precision of localization of epicenters, the correlation between earthquakes and faults became clearer. Authors such as Suess, Koto, Montessus de Ballore, and Sieberg assigned the cause of earthquakes to stresses accumulated in the Earth's crust by tectonic processes and their release by its fracture. The first mechanical model was presented by Reid (1911) in order to explain the origin of the San Francisco earthquake of 1906. His theory, known as elastic rebound, proposes that earthquakes take place by fracturing of the Earth's crust with the total or partial release of the elastic strain accumulated in a region owing to tectonic stress. According to plate tectonics, which was developed in 1960, tectonic stresses are ultimately related to the relative motion of lithospheric plates.

An earthquake can be considered to be produced by rupturing of part of the Earth's crust with a relative displacement of its two sides and the release of the accumulated elastic strain that had been produced by tectonic processes.