The Science of Earthquakes

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** The Science of Earthquakes **

Originally written by Lisa Wald for “The Green Frog News”

-What is an earthquake?-

labeled fault

An /earthquake/ is what happens when two blocks of the earth suddenly slip
past one another. The surface where they slip is called the /fault/ or/
fault plane/. The location below the earth’s surface where the earthquake
starts is called the /hypocenter/, and the location directly above it on
the surface of the earth is called the /epicenter/.

Sometimes an earthquake has /foreshocks/. These are smaller earthquakes
that happen in the same place as the larger earthquake that follows.
Scientists can’t tell that an earthquake is a foreshock until the larger
earthquake happens. The largest, main earthquake is called the /mainshock/.
Mainshocks always have /aftershocks/ that follow. These are smaller
earthquakes that occur afterwards in the same place as the mainshock.
Depending on the size of the mainshock, aftershocks can continue for weeks,
months, and even years after the mainshock!

-What causes earthquakes and where do they happen?-

Earth cross-section

The earth has four major layers: the /inner core, outer core, mantle/ and
/crust/. (figure 2) The crust and the top of the mantle make up a thin skin
on the surface of our planet. But this skin is not all in one piece – it
is made up of many pieces like a puzzle covering the surface of the earth.
(figure 3) Not only that, but these puzzle pieces keep slowly moving


how are earthquakes formed

Earthquake - Wikipedia, the free encyclopedia


** Earthquake **

From Wikipedia, the free encyclopedia
Jump to: navigation, search
For other uses, see Earthquake (disambiguation).
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Global earthquake epicenters, 1963–1998
Global plate tectonic movement

Part of a series on
· · Foreshock
· Aftershock

· · Blind thrust
· Doublet

· · Interplate
· Intraplate

· · Megathrust
· Remotely triggered

· · Slow
· Submarine
· Supershear

· · Tsunami
· Earthquake swarm

· · Fault movement
· Volcanism

· Induced seismicity

· · Epicenter
· Hypocenter

· · Shadow zone
· Seismic wave

· · P-wave
· S-wave

· · Seismic scales
· Seismometer

· Earthquake duration magnitude

· Coordinating Committee for
Earthquake Prediction
· Earthquake-sensitive person

Other topics
· Shear wave splitting
· Adams–Williamson equation
· Flinn-Engdahl regions
· Earthquake engineering
· · Seismite
· Seismology

· v
· t
· e

An *earthquake* (also known as a *quake*, *tremor* or *temblor*) is the
result of a sudden release of energy in the Earth's crust that creates
seismic waves. The *seismicity*, *seismism* or *seismic activity* of an
area refers to the frequency, type and size of earthquakes experienced over
a period of time.

Earthquakes are measured using observations from seismometers. The moment
magnitude is the most common scale on which earthquakes larger than
approximately 5 are reported for the entire globe. The more numerous
earthquakes smaller than magnitude 5 reported by national seismological
observatories are measured mostly on the local magnitude scale, also
referred to as the Richter scale. These two scales are numerically similar
over their range of validity. Magnitude 3 or lower earthquakes are mostly
almost imperceptible or weak and magnitude 7 and over potentially cause
serious damage over larger areas, depending on their depth. The largest


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