Earthquake



Earthquake 2841
Photo by: Christophe Fouquin

An earthquake is an unpredictable event in which masses of rock shift below Earth's surface, releasing enormous amounts of energy and sending out shock waves that sometimes cause the ground to shake dramatically. Not all earthquakes are enormous, but they can become one of Earth's most destructive forces.

Causes of earthquakes

Earth's crust is composed of many huge, rocky plates known as tectonic plates. These plates constantly move slowly across the surface of Earth, bumping into each other, overrunning each other, and pulling away from each other. When the strain produced by these movements increases beyond a certain level, the pent-up energy ruptures the crust and creates a fracture known as a fault. The released pressure also causes the ground-shaking vibrations associated with an earthquake.

The motion of earthquakes: Seismic waves

The vibrations transmitting the shock of an earthquake are called seismic waves (pronounced SIZE-mik). These waves travel outward in all directions, like ripples from a stone dropped in a pond. The area where energy is first released to cause an earthquake is called the focus. The focus lies underground at a shallow, intermediate, or deep depth—down to about 430 miles (700 kilometers). The epicenter is the point on Earth's surface directly above the focus.

Seismic waves travel both through Earth and along its surface. Waves traveling through Earth are called body waves. The two main types are P waves (primary) and S waves (secondary). P waves stretch and compress the rock in their path through Earth. The fastest waves, they move at about 4 miles (6.4 kilometers) per second. S waves move the rock in their path up and down and side to side. They move at about 2 miles (3.2 kilometers) per second.

Words to Know

Epicenter: The location where the seismic waves of an earthquake first appear on the surface, usually almost directly above the focus.

Fault: A crack running through rock that is the result of tectonic forces.

Focus: The underground location of the seismic event that causes an earthquake.

Modified Mercalli scale: A scale used to compare earthquakes based on the effects they cause.

Richter scale: A scale used to compare earthquakes based on the energy released by the earthquake.

Seismic waves: Classified as body waves or surface waves, vibrations in rock and soil that transfer the force of the earthquake from the focus into the surrounding area.

Seismic waves traveling along Earth's surface are called surface waves or L waves (long). The two main types, Rayleigh waves and Love waves, are named after two prominent seismologists (scientists who study earthquakes). Although surface waves move slower than body waves—less than 2 miles (3.2 kilometers) per second—they cause greater damage. Rayleigh waves cause the ground surface in their path to ripple with little waves. Love waves move in a zigzag along the ground. Both Rayleigh and Love waves set off avalanches, landslides, and other earthquake damage.

Measuring earthquakes

An earthquake's power can be measured in two ways: by intensity (strength) and magnitude (ground covered). While intensity of an earthquake is usually described through people's perceptions and the amount of property destroyed, magnitude is measured by using seismographs or devices that detect ground movement.

Intensity can be measured using the modified Mercalli scale. First developed by Italian seismologist Guiseppe Mercalli (1850–1914) in 1902, the scale compares the surface effects of earthquakes to each other. It is divided into 12 levels, from level 1 meaning "felt by few" to level 12 meaning "total damage."

Tsunami

A tsunami is a giant wave created by an underwater earthquake, volcano, or landslide. As part of the seabed (ocean floor) rises or drops, water is displaced or moved, producing a great wave. A tsunami (Japanese for "harbor wave") crosses the deep ocean at speeds up to 500 miles (800 kilometers) per hour, but it is only detectable on the surface as a low swell (a wave with no crest). As the giant wave approaches the shallows near shore, it slows down and rises up dramatically, often as much as 200 feet (60 meters). It then strikes the shore with unstoppable force. A wall of water forms when a large tsunami enters straight into a shallow bay or estuary, and can move upriver for many miles.

Magnitude is measured using the Richter scale, developed by American seismologist Charles F. Richter (1900–1985) in 1935. The Richter scale compares the energy released by an earthquake to the energy released by other earthquakes. Each whole number increase in value on the

A portion of the Hanshin Expressway is twisted down on its side in Nishinomiya after a powerful earthquake rocked the western Japanese city on January 17, 1995. The highway runs from Osaka to Kobe, a port city. Thousands were injured and 1,300 killed. (Reproduced by permission of AP/Wide World Photos.)
A portion of the Hanshin Expressway is twisted down on its side in Nishinomiya after a powerful earthquake rocked the western Japanese city on January 17, 1995. The highway runs from Osaka to Kobe, a port city. Thousands were injured and 1,300 killed. (Reproduced by permission of
AP/Wide World Photos
.)

scale indicates a 10-fold increase in the energy released and a 30-fold increase in ground motion. Therefore, an earthquake of 6 on the Richter scale is 10 times more powerful than an earthquake with a value of 5, which is 10 times more powerful than an earthquake with a value of 4. An earthquake that measures 8 or above on the Richter scale causes total damage.

Earthquake occurrence and prediction

Earth experiences more than one million earthquakes a year. The vast majority of these measure 3.4 or below on the Richter scale and cannot be felt by people. The planet never ceases to vibrate with the motion of its tectonic forces. Full of heat and kinetic energy (the energy of an object due to its motion), Earth has been resounding with the violence of earthquakes for more than four billion years. In recorded human history, great earthquakes have been responsible for some of the most horrendous natural disasters. In the past 800 years, 17 earthquakes have each caused 50,000 or more deaths.

At the beginning of the twenty-first century, an estimated 100 million Americans live on or near an active earthquake fault. Hundreds of millions more lived on or near such faults around the world. Knowing

A National Guardsman walks past all that remains of an apartment house after an earthquake. (Reproduced by permission of Corbis-Bettmann.)
A National Guardsman walks past all that remains of an apartment house after an earthquake. (Reproduced by permission of
Corbis-Bettmann
.)

the exact time and place an earthquake will occur still lies beyond the ability of scientists. However, in order to interpret seismic activity and possibly to prevent needless deaths, seismologists constantly monitor the stresses within Earth's crust. Ultrasensitive instruments placed across faults at the surface measure the slow, almost imperceptible movement of plates. Other instruments measure phenomena that seem to precede earthquakes. These include changes in tide and ground-water levels, fluctuations in the magnetic properties of rocks, and the swelling or tilting of the ground. Peculiar animal behavior has also been reported before many earthquakes, and scientific research into this phenomenon has been conducted.

[ See also Fault ; Plate tectonics ]



Also read article about Earthquake from Wikipedia

User Contributions:

1
chris ryder
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Jan 8, 2007 @ 9:09 am
thanks for the info. when i get on again i will keep lookin at this web site cause u have some good information that i can use on my project.
2
ashfaq
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Jul 16, 2007 @ 3:03 am
i m really interested about this topics. Personally i m a geologist on coal sector but i have a keen interest on eathquake
3
Safeer gul
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Mar 19, 2008 @ 10:22 pm
How to locate a fault line if it is not physically vissible on the ground due to filling of the earth at a place.
4
sushmitha
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Jul 23, 2008 @ 12:12 pm
definitions about earthquakes and tsunami are good.words to know is useful...
5
Gurumurthy
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Sep 10, 2008 @ 12:00 am
Thank you for giving such an intesting article, i realy enjoyed by this.it is so informative, good, interesting.
thanx
6
Emily Ewina
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Sep 28, 2008 @ 4:04 am
Thankyou so much for the use of this fantastic website. I will definatly be using it again and again to help me in my projects. It is clear easy to understand and well presented. I will also be passing the address on to my tutor for Geology as i now he will find it very usful for other students. Thankyou for your great resorces.
7
Shivani
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Oct 10, 2008 @ 6:06 am
This website is very nice. Thank you so much for giving us such an information.
8
Ramya
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Oct 29, 2008 @ 11:23 pm
It is a very nice website . It is very helpful for my projects . Thank you so much .
9
pop
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Dec 2, 2008 @ 11:11 am
HI! Great Website I Think It Is Great! I Will Come Back To Your Website Later!
10
Melissa Morgan
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Feb 15, 2009 @ 7:19 pm
thanks this information helps out alot im studing eathquakes in school.
11
sassy
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Apr 23, 2009 @ 7:07 am
job well done its good to know that some people are actually interested in the unexpected.am a student in year 10 and so am glad to see that we have something in common.
12
Kreslynne Banner
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Apr 28, 2009 @ 3:15 pm
this website was really helpful to me, whenever i need more info i will come here to get it.
13
Emily
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Apr 29, 2009 @ 7:07 am
this is a good site for finding out what causes earthquakes
14
shubhangi
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May 8, 2009 @ 4:04 am
thanks alot of u.i used this info to make my project.when i need some info i will open this website
15
isabella
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May 12, 2009 @ 9:21 pm
wow! i didn't know that earthquakes could be so harmful!
16
Justin Black
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Jul 20, 2009 @ 7:19 pm
I didnt know, what earth quakes were, after reading this sight i now know that earthquakes are caused by tsunamis. I love geology.
17
twebaze michael
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Jul 31, 2009 @ 9:09 am
thanx,my students are blessed with this information, hope they'll pass theier exams well...
18
femtex
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Sep 4, 2009 @ 4:04 am
i m really interested about this topics.because this information helps out alot of people studing surveying and geo-informatics in higher learning.
19
brianna
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Sep 9, 2009 @ 5:17 pm
Wow I realy love the way you guys put this together next time i get on i will
look at more pictures of your earthquakes and write a summary about it.
20
deanna m. williams
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Sep 10, 2009 @ 7:19 pm
hey deanna,here i love the way i can see earthquakes on here.and learn how earthquakes made on this page
21
Mohamed
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Oct 5, 2009 @ 4:16 pm
If i were to be in the middle of a earth quake i would be really scared.I will also kind of stay calm because if you were to be really scared you would throw up and i would not want too throw up.
I would also faint if you were to go crazy screaming an earthquake is coming an earthquake is coming.Stay calm and you will be fine.You would have to stay home for a few days or weeks because of the big crack in the middle of the streets or in the middle of the building.No one knows when a earthquake is going to happen.You would be a genius if you were to know when a earthquake is going to happen.If you were to scream an earthquake is coming and it really came you would have a good mind.
22
jelly
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Oct 6, 2009 @ 4:04 am
Thanks for the information that you generouslly provide to us .I can use the information to do my homework and my research .Thank you
23
reneeka
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Oct 12, 2009 @ 2:14 pm
in class we are learnin this things so continue to put stuff on this site
24
maimela
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Oct 18, 2009 @ 1:13 pm
Now i have an idea of what is happening beneath our earth.please update it regularly as it is something which increases our knowledge.
25
iANKIT
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Oct 20, 2009 @ 6:06 am
IT IS A VERY NICE WEBSITE FOR EARTH QUAKE. THATS PROVIDED A KNOWLEGE OF EARTH QUAKE THANK YOU SO MUCH
26
onel
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Jan 19, 2010 @ 6:06 am
I am interested on that topic and it helps me a lot to enhance my knowledge. Thank you and keep on providing and updating some interesting topics.
27
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Feb 12, 2010 @ 4:04 am
it is nice to know that earthquake is a big disaster in global realms. nice website i get some knowledge and information about it. more power and god bless.
28
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Jun 22, 2010 @ 4:04 am
very good report i liked it so much it is very good to read
29
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Jul 29, 2010 @ 4:16 pm
Can you explain to me the energy transfers and transformations involved in L-waves as they travel along the earth's crust.

Thanks

Kwadwo
30
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Jan 29, 2011 @ 11:23 pm
I HAD A PROJECT ON WHICH WE HAD TO EXPLAIN ABOUT THE PROBLEMS OF EARTHQUAKE AND HELP THEM
31
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Feb 10, 2011 @ 1:13 pm
This is a good website that has a lot of info. Thanx
32
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Feb 15, 2011 @ 5:17 pm
i am very glad that you put such a useful facts about earthquake.It help me alot .thank you.
33
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Mar 12, 2011 @ 3:15 pm
I am so glad about all this infos but i actually want to say that we must be very careful to avoid this wicked earthquake by avoiding man made explosion etc.
34
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Mar 14, 2011 @ 2:02 am
how the japan quake affect the geophysical, hydospheric and atmospheric landscape of the planet earth.?
35
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Apr 27, 2011 @ 4:16 pm
This site is the most informative that I'v ever been on.I will make sure to come here again.
36
soraya
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May 17, 2011 @ 6:18 pm
This website is so amazing. It has EVERYTHING i need to study for my test. I recomend it to anyone with eyes.
37
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Jun 5, 2011 @ 8:08 am
I got very much knowlege from this article thk u very much
38
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Nov 26, 2011 @ 2:02 am
This website is so helpful to us, now i have a answer for my project, i will always visit this website for more information about earthquake.
39
V Li
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Dec 7, 2012 @ 6:18 pm
This website has saved me from a lot of trouble with homework about science! I didn't even know that earthquakes could be this harmful until I read this article! Thank you!
40
Booboo
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Dec 10, 2012 @ 1:13 pm
Its mooshy its squishy, it smells like a toohsy, what is it, what is it? Its diaria!
41
nautica
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Feb 3, 2015 @ 11:11 am
I used all this information for my project in science and I got an a+
42
Mdees
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Apr 2, 2015 @ 4:16 pm
Used info for my research for science My grade was an 98

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