USGS Earthquake Hazards Program-FAQ - Frequently Asked Questions

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background="/web/20051120192226im_/http://earthquake.usgs.gov/images/quakebg.gif" alt="background image"> <tr> <td valign="top"> <center> Frequently Asked Questions <hr/> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/">FAQ Home</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/current.html">Current EQs</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/myths.html">Myths</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/plates.html">EQs,Faults,etc</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/meas.html">Measuring EQs</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/seismo.html">Seismographs</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/effects.html">EQ Effects</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/hazard.html">Hazards</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/myths.html">Prediction</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/hist.html">Historic EQs</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/nuclear.html">Nuclear Explosion</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/regional.html">Regional</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/prepare.html">Preparedness</a> <a href="/web/20051120192226/http://earthquake.usgs.gov/faq/resources.html">Other Resources</a>   </center> </td> </tr> </table> </td>  <td width="100%" bgcolor="#FFFFFF" valign="top">  <table width="100%" border="0" cellspacing="0" cellpadding="7"> <tr valign="top"> <td class="bodytext"> <center> Regionally-specific Earthquake Information <a name="1" id="1"></a> <table border="0" width="100%"> <tr> <td bgcolor="#ffffff"> These various links are devoted to specific regions: <blockquote> <a href="https://web.archive.org/web/20051120192226/http://neic.usgs.gov/neis/states/states.html">By State</a> - NEIC </blockquote> FAQs & Earthquake Information: <blockquote> Alaska <a href="https://web.archive.org/web/20051120192226/http://www.aeic.alaska.edu/">Alaska Earthquake Information Center</a> <a href="https://web.archive.org/web/20051120192226/http://wcatwc.gov/">NOAA West Coast & Alaska Tsunami Warning Center</a> Washington/Oregon <a href="https://web.archive.org/web/20051120192226/http://www.pnsn.org/INFO_GENERAL/faq.html">Pacific Northwest Seismic Network</a> - Univ. of Washington <a href="https://web.archive.org/web/20051120192226/http://sarvis.dogami.state.or.us/earthquakes/earthquakehome.htm">Oregon Dept of Geology & Mineral Industries </a> California <a href="calif.html">California FAQ</a> <a href="https://web.archive.org/web/20051120192226/http://quake.wr.usgs.gov/">USGS - Northern California</a> <a href="https://web.archive.org/web/20051120192226/http://pasadena.wr.usgs.gov/">USGS - Southern California</a> <a href="https://web.archive.org/web/20051120192226/http://gmw.consrv.ca.gov/shmp/">California Geological Survey</a> <a href="https://web.archive.org/web/20051120192226/http://www.seismo.berkeley.edu/seismo/faq/faq.html">UC Berkeley</a> <a href="https://web.archive.org/web/20051120192226/http://www-ida.ucsd.edu/ANZA/home.html">ANZA Network</a> - U.C. San Diego <a href="https://web.archive.org/web/20051120192226/http://www.data.scec.org/">Southern California Earthquake Data Center</a> <a href="https://web.archive.org/web/20051120192226/http://quake.geo.berkeley.edu/">Northern California Earthquake Data Center</a> Montana <a href="https://web.archive.org/web/20051120192226/http://mbmgsun.mtech.edu/quakesm.htm">Montana Bureau of Mines & Geology</a> Nevada <a href="https://web.archive.org/web/20051120192226/http://www.seismo.unr.edu/Perminfo/question_answer.html">Nevada Seismological Laboratory</a> Utah <a href="https://web.archive.org/web/20051120192226/http://www.seis.utah.edu/HTML/UtahsEarthquakeThreat2.html">Univ. of Utah Seismograph Stations </a> <a href="https://web.archive.org/web/20051120192226/http://www.seis.utah.edu/edservices/EES/EES.html">Univ. of Utah Earthquake Education Services</a> Central US/New Madrid <a href="https://web.archive.org/web/20051120192226/http://neic.usgs.gov/">USGS National Earthquake Information Center</a> <a href="https://web.archive.org/web/20051120192226/http://www.ceri.memphis.edu/">Center for Earthquake Research and Information</a> (CERI) - Univ. of Memphis <a href="https://web.archive.org/web/20051120192226/http://www.eas.slu.edu/Earthquake_Center/">St. Louis University Earthquake Center</a> <a href="https://web.archive.org/web/20051120192226/http://neic.usgs.gov/neis/general/faults_east.html">Where Are the Fault Lines in the U.S. East of the Rocky Mountains?</a> <a href="https://web.archive.org/web/20051120192226/http://neic.usgs.gov/neis/general/faq.html"> </a> <a name="2" id="2"></a>East Coast/New England <table border="0" width="100%"> <tr> <td bgcolor="#FFCC00"> Q: Why should people in the eastern US be concerned about earthquakes?   </td> </tr> <tr> <td bgcolor="#ffffff"> A: a) Severe earthquakes have occurred in the East: <blockquote> In November of 1755, an earthquake with an estimated magnitude of 6.0 and a maximum intensity of VIII occurred 200 miles off the coast of Cape Ann, Massachusetts. Boston was heavily damaged. The strongest earthquakes recorded in the continental US were not in the West; they were centered in eastern Missouri near the border with Kentucky and Tennessee. In the winter of 1811-1812, a series of three earthquakes of magnitudes 8.4 to 8.7 and maximum intensities of XI occurred near New Madrid, Missouri. These shocks were so strong that observers reported that the land distorted into visible rolling waves. They changed the course of the Mississippi River; they made church bells ring in Boston and Washington, D.C. Because the surrounding area was mostly undeveloped at the time, few deaths were reported and these events stirred relatively little attention then. In August of 1886, a strong earthquake occurred in Charleston, South Carolina. Magnitude is estimated at 6.6 and maximum intensity was X. Most of the city of Charleston was damaged or destroyed. Earthquakes in the East are not confined to these areas; they have been recorded in every State east of the Mississippi. Damaging earthquakes have occurred historically in nearly every eastern State. </blockquote> b) Earthquakes of the same magnitude affect larger areas in the East than in the West: <blockquote> The size of the geographic area affected by ground shaking depends on the magnitude of the earthquake and the rate at which the amplitudes of body and surface seismic waves decrease as distance from the causative fault increases. Comparison of the areas affected by the same Modified Mercalli intensity of ground shaking in the 1906 San Francisco, California, the 1971 San Fernando, California, the 1811-12 New Madrid, Missouri, and the 1886 Charleston, South Carolina, earthquakes shows that a given intensity of ground shaking extends over a much larger area in the Eastern United States. Ground shaking affects a larger area because amplitudes of seismic waves decrease more slowly in the east than in the west as distance from the causative fault increases. <img src="/web/20051120192226im_/http://earthquake.usgs.gov/faq/images/east.gif" width="538" height="347" alt="geographic area effected by shaking"/> Comparison of isoseismal contours for a great earthquake, the 1906 San Francisco; a moderate earthquake, the 1971 San Fernando; and two large earthquakes, the 1811-12 New Madrid and 1886 Charleston. The contour lines connect sites having the same value of Modified Mercalli intensity, a numerical index of the effects of an earthquake on man, the Earth's surface, and on buildings. Each area shown in red corresponds to an intensity of VII or greater and denotes the zone of most severe ground shaking and damage. The area shaded blue corresponds to an intensity of VI; in this area, the ground shaking is felt by all, many are frightened and run outdoors, but damage is slight. The effects of ground shaking extend over a much larger area in the Eastern United States. Taken from: Hays, W.W., ed., 1981, Facing Geologic and Hydrologic Hazards -- Earth Science Considerations: U.S. Geological Survey Professional Paper 1240B, 108 p. </blockquote> c) Eastern state's building codes: <blockquote> Modern building codes in Eastern states are not as strict as those in California and much of the West: Not only that, but older buildings, which predate modern building codes completely, are more prevalent in the East than in the West. </blockquote> d) Causes of earthquakes in the East are not well-understood: <blockquote> Hundreds of millions of years ago, the East coast was this continent's active plate tectonic boundary, as the West coast is today. If the East is not now in an active plate margin, why do we have earthquakes here and why do we have them in the center of the continent? One possible explanation is that ancient faults or rifts are stressed. If this is true, what is the cause of the stress? In many areas of the East where earthquakes have occurred historically, specific faults causing the quakes have not been mapped or even identified. Another problem we encounter when evaluating earthquake risk is that we only have earthquake records for the last couple of hundred years. Establishing geologic patterns over human time scales is difficult at best. </blockquote> For further information: <a href="https://web.archive.org/web/20051120192226/http://neic.usgs.gov/neis/general/faults_east.html">Where Are the Fault Lines in the U.S. East of the Rocky Mountains?</a> </td> </tr> </table> See also: <a href="https://web.archive.org/web/20051120192226/http://www.ldeo.columbia.edu/LCSN/">Lamont-Doherty Cooperative Seismic Network</a> <a href="https://web.archive.org/web/20051120192226/http://www.bc.edu/bc_org/avp/cas/wesobs/">Westin Observatory</a> at Boston College <a href="https://web.archive.org/web/20051120192226/http://nceer.eng.buffalo.edu/faqs/">MCEER</a> - New York <a href="https://web.archive.org/web/20051120192226/http://vtso.geol.vt.edu/outreach/vtso/">Virginia Tech Seismological Observatory</a> <a href="https://web.archive.org/web/20051120192226/http://www.mgs.md.gov/esic/brochures/earthquake.html">Earthquakes & Maryland</a> - Maryland Geological Survey Puerto Rico <a href="https://web.archive.org/web/20051120192226/http://rmsismo.upr.clu.edu/">Puerto Rico Seismic Network</a>, University of Puerto Rico Other Regions See links listed for each region at <a href="https://web.archive.org/web/20051120192226/http://earthquake.usgs.gov/recenteqsww/">World Current Seismicity Maps</a> or try <a href="https://web.archive.org/web/20051120192226/http://www.geophys.washington.edu/seismosurfing.html">Seismosurfing</a> </blockquote> </td> </tr> </table> <a href="index.html">Back to Earthquake FAQ Main page</a> </center>  </td> </tr> </table> </td> </tr>  </table>  <table width="100%" bgcolor="#000000" border="0" cellspacing="0" cellpadding="0"> <tr> <td><img src="/web/20051120192226im_/http://earthquake.usgs.gov/images/shim.gif" width="1" height="1" alt="spacer"/></td> </tr> </table> <table width="100%" border="0" cellspacing="0" cellpadding="5" bgcolor="#FFFFFF"> <tr valign="top"> <td> <a href="https://web.archive.org/web/20051120192226/http://www.doi.gov/">U.S. Department of the Interior, </a><a href="https://web.archive.org/web/20051120192226/http://www.usgs.gov/">U.S. Geological Survey</a> This page is brought to you by the Earthquake Hazards Program URL: http://earthquake.usgs.govfaq/ Maintained by: Web Team Last modification: Tuesday, 12-Oct-2004 11:16  Contact Us:<a href="/web/20051120192226/http://earthquake.usgs.gov/cgi-bin/sitemail1.cgi?docname=Web_Team">  Web_Team</a> USGS <a href="https://web.archive.org/web/20051120192226/http://www.usgs.gov/privacy.html">Privacy Statement</a> | | <a href="https://web.archive.org/web/20051120192226/http://www.usgs.gov/disclaimer.html">Disclaimer</a> | | <a href="https://web.archive.org/web/20051120192226/http://www.usgs.gov/foia/">FOIA</a> | | <a href="https://web.archive.org/web/20051120192226/http://www.usgs.gov/accessibility.html"> Accessibility</a> </td> <td> <div align="right"><a href="https://web.archive.org/web/20051120192226/http://firstgov.gov/"><img src="/web/20051120192226im_/http://earthquake.usgs.gov/images/first_gov.gif" width="160" height="47" alt="First Government graphic" border="0"/></a></div> </td> </tr> </table> </body> </html>

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USGS Earthquake Hazards Program-FAQ - Frequently Asked Questions