Earthquake
Article by: Christopher H. Scholz, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York.
Kaye M. Shedlock, Geological Hazards Section, U.S. Geological Survey, U.S. Department of the Interior, Denver, Colorado
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A sudden movement of the Earth caused by the abrupt
release of accumulated strain along a fault in the interior.
The released energy passes through the Earth as seismic waves
(low-frequency sound waves), which cause the shaking.
Seismic waves continue to travel through the Earth after the
fault motion has stopped. Recordings of earthquakes, called
seismograms, illustrate that such motion is recorded all over
the Earth for hours, and even days, after an earthquake. Earth-
quakes are one of the most destructive natural phenomena and
occur with very little warning (Fig. 1). As a result, earthquake
early warning, or seismic alert, systems are being implemented
in earthquake-prone cities and regions.
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Content
• Characteristics
• Cause
• Stick-slip friction and
elastic rebound
• Classification
• Sequences
• Size
• Effects
• Prediction
• Deep earthquakes
Fig. 1: Destruction and debris following the magnitude 9 Japan, 2011 (Fukushima)
earthquake and tsunami. (Credit: MC1 Matthew M. Bradley/US Navy)
Key Concepts
• Among the most destructive of Earth's natural phenomena, earthquakes are sudden
ground movements caused by the abrupt release of strain along a fault in Earth's
interior, resulting in the propagation of seismic waves.
• The vast majority of earthquakes occur on or near lithospheric plate boundaries,
which are in continuous motion.
• Earthquakes often occur in well-defined sequences in time, but can range
enormously in size.
• Earthquake size is measured by seismic moment. An older measure of earthquake
size is magnitude, which is proportional to the logarithm of moment.
• The intensity of an earthquake is a measure of the severity of shaking and its
attendant damage at a point on Earth's surface, and usually decreases with
distance from the epicenter.
• While precise forecasting of earthquakes has remained unachievable, rough
forecasts can be issued based on seismic gaps and probability estimates.
