Quaking, Shaking, Earth All about Earthquakes Main Source: //.

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Quaking, Shaking, Earth All about Earthquakes Main Source: http://www.thesciencequeen.net/7Units.htm

Transcript of Quaking, Shaking, Earth All about Earthquakes Main Source: //.

Quaking, Shaking, Earth

All about EarthquakesMain Source: http://www.thesciencequeen.net/7Units.htm

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What is an earthquake?

• Simply put:– An earthquake is the shaking of the earth.

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Many buildings in Charleston,

South Carolina, were damaged or destroyed by

the large earthquake that

occurred August 31,

1886.

Picture from the United States Geological Service www.usgs.gov

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San Francisco, California, Earthquake April 18, 1906. East side of Howard Street near Seventeenth Street. All houses shifted toward the left. The tall house dropped from its south foundation wall and leaned against its neighbor. 1906.

Picture from USGS.GOV

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San Fernando, California, Earthquake February 1971. Collapsed overpass connecting Foothill Boulevard and the Golden State Freeway. Feb 10, 1971.

Photo by R.E. Wallace, USGS.

www.usgs.gov

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What causes an earthquake?

• Earthquakes are the Earth's natural means of releasing stress.

• Due to the constant motion of the Earth’ plates, this put stress on the edges of the plates.

• To relieve this stress, the rocks tend to bend, compress, or stretch.

An aerial view of the San Andreas fault in the Carrizo Plain, Central California. Picture from www.usgs.gov

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Locatin' the Shakin'

• Focus: the place on the Earth’s crust where the pressure was released.

• Epicenter: the spot on the Earth’s surface directly above the focus.

http://geomaps.wr.usgs.gov/parks/deform/

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Faults

• If the force is great enough, the rocks will break.

• An earthquake is the vibrations produced by the breaking of rock.

• Most earthquakes occur near plate boundaries.

The Hanshin expressway in Kobe, Japan collapsed due to an earthquake in 1995.Picture from http://www.ce.washington.edu/~liquefaction/html/quakes/kobe/kobe.html

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Normal Fault

• Drops rock on one side of the fault down relative to the other side.

http://earthquake.usgs.gov/regional/imw/images/figure1.php

Wasatch Fault - Utah

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Reverse Fault

• Reverse faults result from compression forces that squeeze rock.

• If rock breaks from forces pushing from opposite directions, rock above a reverse fault surface is forced up and over the rock below the fault surface.

Near Klamath Falls, Oregon

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http://pages.uoregon.edu/millerm/KlamT.jpeg

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Strike-slip Fault

• At a strike-slip fault, rocks on either side of the fault are moving past each other without much upward or downward movement.

• The San Andreas Fault is the boundary between two of Earth’s plates that are moving sideways past each other.

San Andreas Fault, California

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The Pacific Plate lies to the west of the San Andreas Fault and the North American Plate lies to the east. Scientists have determined that the Pacific Plate moves northwest at the rate of about two inches every year relative to the North American Plate. The western half of California lies on the Pacific Plate while the eastern half of California lies on the North American Plate. Besides the short term effects of being an earthquake ‘hot zone’, western California will, in about one million years, be part of Alaska (assuming Alaska stays put), as the Pacific Plate continues its northwesterly trek.

https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcTyQlHA1d9NDVUSO_qxad6t2yJ3LanXsVzZF0tfUArgNQ-9j0-U

https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcTtVYa8xuT5pBjFVLP_sYSa_GrFZqFQO9LTpEaDht6N3CUvjP7hZA

http://www.platetectonics.com/book/page_15.asp

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How does energy created by an earthquake move through the

Earth?• Seismic waves

are energy waves that travel outward from the source of the earthquake.

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Surfin the Waves

• When earthquakes occur, three different types of seismic waves are produced.

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P Waves• Primary waves (P-

waves) cause particles in rocks to move back and forth in the same direction that the wave is traveling.

• P-Waves are the fastest waves and are felt first, usually as a bang or a thump.

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S Waves

• Secondary waves (S-waves) move through Earth by causing particles in rocks to move at right angles to the direction of wave travel.

• These waves are slower than P-Waves.

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L Waves

• Surface waves cause most of the destruction resulting from earthquakes.

• Surface waves (L-Waves) or land waves move rock particles in a backward, rolling motion and a side-to-side, swaying motion.

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How are seismic waves measured?

• Seismic waves from earthquakes are measured with an instrument known as a seismograph.

• Seismographs register the waves and record the time that each arrived.

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Measuring Earthquake Magnitude

•Magnitude is a measure of the energy that is released during an earthquake.

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Richter Scale

• The Richter magnitude scale is used to describe the strength of an earthquake and is based on the height of the lines on the seismogram.

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Richter Scale

• For each increase of 1.0 on the Richter scale, the height of the line on a seismogram is ten times greater.

• However, about 32 times as much energy is released for every increase of 1.0 on the scale.

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Earthquake Severity

• Richter Earthquake Magnitudes Effects• Less than 3.5 Generally not felt, but recorded. • 3.5-5.4 Often felt, but rarely causes damage. • Under 6.0 At most slight damage to well-designed

buildings. Can cause major damage to poorly constructed buildings over small regions.

• 6.1-6.9 Can be destructive in areas up to about 100 kilometers across where people live.

• 7.0-7.9 Major earthquake. Can cause serious damage over larger areas.

• 8 or greater Great earthquake. Can cause serious damage in areas several hundred kilometers across.

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Magnitude ChangeGround Motion

Change (Displacement)

Energy Change

1.0 10.0 times about 32 times

0.5 3.2 times about 5.5 times

0.3 2.0 times about 3 times

0.1 1.3 times about 1.4 times

This table shows that a magnitude 7.2 earthquake produces 10 times more ground motion than a magnitude 6.2 earthquake, but it releases about 32 times more energy. The energy release best indicates the destructive power of an earthquake.

Magnitude vs. Ground Motion and Energy

http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php

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Magnitude Average Annually

8 and higher 1 ¹

7 - 7.9 15 ¹

6 - 6.9 134 ²

5 - 5.9 1319 ²

4 - 4.913,000

(estimated)

3 - 3.9130,000

(estimated)

2 - 2.91,300,000

(estimated)

¹ Based on observations since 1900. These numbers have been recently updated, based on data from the Centennial catalog (from 1900 to 1999) and the PDE (since 2000). ² Based on observations since 1990.

http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php

Frequency of Earthquakes

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Recent Large Magnitude Earthquakes

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