| earthquake (ûrth'kwāk') A sudden movement of the Earth's lithosphere (its crust and upper mantle). Earthquakes are caused by the release of built-up stress within rocks along geologic faults or by the movement of magma in volcanic areas. They are usually followed by aftershocks. See Note at fault. Our Living Language : Fractures in Earth's crust, or lithosphere, where sections of rock have slipped past each other are called faults. Earthquakes are caused by the sudden release of accumulated strain along these faults, releasing energy in the form of low-frequency sound waves called seismic waves. Although thousands of earthquakes occur each year, most are too weak to be detected except by seismographs, instruments that detect and record vibrations and movements in the Earth. The point where the earthquake originates is the seismic focus, and directly above it on Earth's surface is the earthquake's epicenter. Three kinds of waves accompany earthquakes. Primary (P) waves have a push-pull type of vibration. Secondary (S) waves have a side-to-side type of vibration. Both P and S waves travel deep into Earth, reflecting off the surfaces of its various layers. S waves cannot travel through the liquid outer core. Surface (L) waves—named after the nineteenth-century British mathematician A.E.H. Love—travel along Earth's surface, causing most of the damage of an earthquake. The total amount of energy released by an earthquake is measured on the Richter scale. Each increase by 1 corresponds to a tenfold increase in strength. Earthquakes above 7 on the Richter scale are considered severe. The famous earthquake that flattened San Francisco in 1906 had a magnitude of 7.8. |
A tremor of the surface of the Earth, sometimes severe and devastating, which results from shock waves generated by the movement of rock masses deep within the Earth, particularly near boundaries of tectonic plates. (See fault, Richter scale, and seismology.)
Note: Earthquakes are particularly likely where such plates are sliding past each other, as in the San Andreas Fault.
Note: Earthquakes cannot be accurately predicted, although the likelihood of a region's suffering an earthquake can be estimated.
mentioned among the extraordinary phenomena of Palestine (Ps. 18:7; comp. Hab. 3:6; Nah. 1:5; Isa. 5:25). The first earthquake in Palestine of which we have any record happened in the reign of Ahab (1 Kings 19:11, 12). Another took place in the days of Uzziah, King of Judah (Zech. 14:5). The most memorable earthquake taking place in New Testament times happened at the crucifixion of our Lord (Matt. 27:54). An earthquake at Philippi shook the prison in which Paul and Silas were imprisoned (Act 16:26). It is used figuratively as a token of the presence of the Lord (Judg. 5:4; 2 Sam. 22:8; Ps. 77:18; 97:4; 104:32).