Earthquakes, damage and its mitigation

Earthquake Occurrence

A worldwide network of sensitive seismographs that have operated this century has now mapped in a reliable way the pattern of all significant seismic activity of the Earth. An explanation for the uneven distribution is given by the theory of plate tectonics. First, most earthquakes occur along the edges of the interacting tectonic plates (interplate earthquakes) but a few, including some of large magnitude (such as the 1811–12 New Madrid earthquakes in the United States) occur within the plate (intraplate earthquakes). In some seismically active areas, such as along the margins of South America, Alaska and Japan (Benioff zones), plate convergence results in crustal rocks plunging down (subducting) deep into the Earth. These convergent plate boundaries contribute more than 90 per cent of the Earth's release of seismic energy for shallow earthquakes, as well as most of the energy for intermediate and deep-focus earthquakes (down to 680 km depth). Most of the...