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  • GEORGIAGEORGIA EARTHQUAKE EARTHQUAKE

    AWARENESS GUIDEAWARENESS GUIDE

    For Local Emergency Management For Local Emergency Management For Local Emergency Management Agency Directors Agency Directors Agency Directors

    April 2011

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  • This publication is a project of the Georgia Emergency Management Agency (GEMA)/Homeland Security in cooperation with the Georgia Institute of Technology-School of Earth & Atmospheric Science, the Federal Emergency Management Agency (FEMA) National Earthquake Hazards Reduction Program (NEHRP) and the Ready Georgia Campaign. A downloadable guide is available at:

    www.gema.ga.gov www.ready.ga.gov

    http://geophysics.eas.gatech.edu For additional information, please contact GEMA or Georgia Institute of Technology, School of Earth & Atmospheric Sciences.

    Agency Website Address Phone Number

    Georgia Emergency Management Agency/Homeland Security Ready Georgia Campaign

    www.gema.ga.gov www.ready.ga.gov

    P.O. Box 18055 Atlanta, Georgia 30316

    1-800-TRY-GEMA

    Georgia Institute of Technology-School of Earth & Atmospheric Sciences

    http://www.eas.gatech.edu/schoo

    311 Ferst Drive Atlanta, GA 30332-0340

    404-894-3893

    April 2011

  • TableofContentsGeorgia and Earthquakes PAGE 1

    Earthquake Basics Overview PAGE 3

    U.S. Seismicity PAGE 8

    Largest U.S. Earthquakes PAGE 9

    Georgia Earthquake History PAGE 10

    Georgia Earthquake Risk PAGE 12

    Planning for Earthquakes PAGE 16

    FIGURES

    Figure 1.0: Georgia Counties at the Greatest Risk for Earthquakes

    Figure 2.0: Types of Faults

    Figure 3.0: Modified-Mercalli Intensity Map

    Figure 4.0: U.S. Earthquakes Facts & Statistics

    Figure 5.0: U.S. Earthquakes Causing Damage 1750-1996

    Figure 6.0: USGS Seismic Hazard Map

    Figure 7.0: The National Seismic Hazard Map

    ADDITIONAL RESOURCES

    Information Sources

    Glossary of Terms Descriptive Comparisons of Earthquake Magnitude with Observed Effects Modified-Mercalli Intensity Scale of 1931

  • GEORGIA EARTHQUAKE AWARENESS GUIDE GEORGIA EARTHQUAKE AWARENESS GUIDE 111

    1

    GEORGIA AND EARTHQUAKESGEORGIA AND EARTHQUAKES

    According to Georgia Techs School of Earth and Atmospheric Sciences, 15 percent of the worlds earthquakes are scattered over areas like Georgia that lack clearly defined active faults. These earthquakes usually start with a jolt, build rapidly in amplitude within a couple of seconds, and then decay.

    The total felt duration of the typical small Georgia earthquake is usually less than 10 seconds, and it sounds like a muffled dynamite explosion. Although earthquakes in Georgia are comparatively rare, scattered earthquakes have caused significant damage and can be an important consideration for homeowners (Source: www.ready.ga.gov).

    Figure 1.0: Georgia Counties at the Greatest Risk for Earthquakes

    Area Counties

    Northwest Georgia Counties Bartow, Catoosa, Chattooga, Dade, Fannin, Floyd, Gilmer, Gordon, Murray, Pickens, Rabun, Towns, Union, Walker, Whitfield

    South Carolina Border Counties Burke, Chatham, Columbia, Effingham, El-bert, Lincoln, Richmond, Screven

    Source: Georgia Tech School of Earth & Atmospheric Sciences, A.V. Newman, C.N. Gam-mans, 2010.

    Central and West Central Georgia Counties

    Twiggs, Bibb, Jones, Baldwin, Hancock, Greene, Putnam, Butts, Jasper, Newton, Morgan, Walton, Harris, Mucscogee

  • GEORGIA EARTHQUAKE AWARENESS GUIDE GEORGIA EARTHQUAKE AWARENESS GUIDE 222

    2

  • GEORGIA EARTHQUAKE AWARENESS GUIDE GEORGIA EARTHQUAKE AWARENESS GUIDE 333

    3

    EARTHQUAKE BASICS OVERVIEWEARTHQUAKE BASICS OVERVIEW An earthquake is a sudden shaking of the earth caused by the breaking and shifting of rock beneath the earth's surface. Earthquakes can cause buildings and bridges to collapse, telephone and power lines to fall, and cause fires, explosions and landslides. Earthquakes can also cause tsunamis, which can impact coastal areas far away from where earthquake shaking can be felt.

    Earthquake Effects

    Earthquakes often have significant social and economic impacts on communities, including:

    Disruption of business supply chains;

    Rise in insurance costs for certain types of buildings susceptible to earthquake damage;

    Cancellation of insurance policy after an earthquake;

    Loss of housing options (especially for low-income residents);

    Changes to neighborhoods, as residents often must relocate.

    Causes of Earthquakes

    An earthquake is caused by a sudden slip on a fault, which results in a release of energy that travels away from the fault surface as seismic waves. Seismic waves are elastic shocks that travel through the earth. Faults slip to release stress that is created as tectonic plates move around the surface of the earth.

  • GEORGIA EARTHQUAKE AWARENESS GUIDE GEORGIA EARTHQUAKE AWARENESS GUIDE 444

    4

    Faults

    A fault is a weak zone in the earth's crust where two sections can shift.

    Normal fault movement occurs when the two sides move away from one another as the crust fails in extension.

    Thrust or reverse fault movement occurs when the two sides are pushed together due to compression.

    Strike-slip or lateral fault movement occurs when the pieces move horizontally past one another.

    Figure 2.0: Types of Faults

    Source: http://www.dnr.sc.gov/geology/earthquake.html

    Seismic Waves

    Earthquakes release energy that radiates away from the fault in the form of seismic waves.

    The two main types of seismic waves are:

    Body waves

    Surface waves

  • GEORGIA EARTHQUAKE AWARENESS GUIDE GEORGIA EARTHQUAKE AWARENESS GUIDE 555

    5

    Body Waves

    Travel through the Earth

    Are felt first after an earthquake

    Can be divided into:

    o Compressional Waves (also called primary or P waves) are the fastest seismic waves traveling as fast as 30 times the speed of sound in air.

    o Shear Waves (or secondary waves) are the second main arrival, traveling at about 60% the speed of P waves.

    Surface Waves

    Travel along the Earth's surface

    Travel slower than either type of body wave

    Are larger then body waves for most earthquakes

    Cause most of the damage to buildings

    Measuring Earthquakes

    Seismographs record and measure vibrations produced by earthquakes as a wavy line called a seismogram. Modern seismographs record earthquakes digitally, rather than on paper allowing for greater research and storage capabilities.

    Using the data recorded as seismograms by many recording stations, the following can be determined:

    Time the earthquake started

    Epicenter of the quake (where it started)

    Focal depth

    Amount of energy released (related to the magnitude)

    Fault area

  • GEORGIA EARTHQUAKE AWARENESS GUIDE GEORGIA EARTHQUAKE AWARENESS GUIDE

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