noun
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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.
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See Note at fault
Closer Look
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.
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Earthquakes are particularly likely where such plates are sliding past each other, as in the San Andreas Fault.
Earthquakes cannot be accurately predicted, although the likelihood of a region's suffering an earthquake can be estimated.
Other Word Forms
- preearthquake adjective
Etymology
Origin of earthquake
1300–50; Middle English erthequake ( earth, quake ), replacing Old English eorthdyne ( din 1 )
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
"I thought it was an earthquake. I was sitting down and I fell on the floor, along with the other passengers," one man told Ansa news agency.
From BBC
The team also deployed seismic instruments that detected a series of glacier earthquakes during the period of rapid retreat.
From Science Daily
Around 880 tonnes of hazardous material remain inside the power station, the site of one of the world's worst nuclear accidents after a tsunami was triggered by a 9.0-magnitude earthquake.
From Barron's
Microsoft's Jakarta facilities, spread out to mitigate risks from earthquakes and floods, are part of a $1.7 billion investment with a potential "hyperscale" capacity that would need hundreds of megawatts of electricity.
From Barron's
Under certain conditions, these forces might contribute to the start of large earthquakes.
From Science Daily
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
