What are earthquakes?

• Earthquakes occur mainly at plate boundariesplate boundaries.

http://vulcan.wr.usgs.gov/Imgs/Gif/PlateTectonics/Maps/map_quakes_volcanoes_plates.gif

Pressure

• Pressure builds up as plates move.

• Eventually rocks break at a faultfault.

• Energy is released as seismic seismic waveswaves. (3 kinds)

Types of Forces and Faults

Normal Faults

Tension – pulling rocks apart

Reverse Faults

Compression– pushing rocks together

Strike-Slip Faults

• Caused by shearing

Describing the location

Earthquakes occur underground. The spot underground where the rock breaks

is the focusfocus. The spot on the surface directly above that is

the epicenterepicenter.

http://www.harcourtschool.com/scienceglossary/images/gr4/epicenter4.jpg

Types of Waves

Primary WavesPrimary Waves (first) – longitudinal waves that travel the fastest- originate at the focus

These are the first sign of an earthquake

http://astro.uchicago.edu/cara/outreach/se/ysi/1999/intro2.html

Secondary Waves

Transverse Waves that start out at the focus

http://astro.uchicago.edu/cara/outreach/se/ysi/1999/intro2.html

Surface Waves

Originate at the epicenter (on the surface)

Cause the most destruction

http://www.gly.fsu.edu/~salters/GLY1000/Chapter4/Slide18.jpg

How far away?

• The lag time between the primary and secondary waves is used to determine how far away the earthquake occurred

Measuring an Earthquake

SeismometersSeismometers – instruments used to sense and record earthquake data

http://www.thetech.org/exhibits/online/quakes/seismo/

Measuring an Earthquake

SeismographsSeismographs – recordings of seismic waves produced by seismometers

http://www.thetech.org/exhibits/online/quakes/seismo/

http://www.inel.gov/env-energyscience/seismic/network.shtml

Amplitude

• The height of a wave

Locating the epicenter

3 Seismograph stations are required to triangulate the location

http://www.tecedu.com/about/images/us-map.gif

Richter ScaleMeasures the magnitude of earthquakes

using the distance from the epicenter and the amplitude of the largest wave.

http://www.wanadoo.jo/medias/img/SGE.GXY52.050904182653.photo00.default-245x208.jpg

Determining Richter scale

Richter ScaleEach number increase on the Richter

scale indicates an increase of

10x’s in amplitude

32 x’s more energy

http://www.wanadoo.jo/medias/img/SGE.GXY52.050904182653.photo00.default-245x208.jpg

Historic Earthquakes

Alaska 1964, 9.2

http://epod.usra.edu/archive/images/augustanack3.jpghttp://earth.geol.ksu.edu/sgao/g100/plots/1031_earthquake_trig.jpg

http://www.tfhrc.gov/pubrds/03nov/images/mccarthy2.jpg

http://www.tfhrc.gov/pubrds/03nov/05.htmhttp://www.disasterrelief.org/Disasters/010326alaskaquake1964/Images/rail.gif

Modified Mercalli Scale

Measures intensity or damage caused by an earthquake

I -XII

http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf

Moment magnitude scale

Used to record energy released by an earthquake and takes into account the size of the fault rupture.

Tsunamis

• are large fast moving waves that are produced by moving crust under the ocean

Recent Tsunami’s

What are earthquakes?

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