Hypocenter(redirected from Earthquake foci)
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the focal point of an earthquake. The depth at which a hypocenter lies can vary from 0 to 700 km. The source of underground shock is movements along tectonic faults, which vary in length up to hundreds of kilometers. In this sense, the hypocenter means the point from which the fault began to rip open. In the upper parts of the earth’s crust (up to 20 km) the hypocenter occurs as a result of brittle deformations in a rock series. Deeper hypocenters arise where plastic deformations prevail.