usually caused by earthquakesor submarine landslides) struckcoastal areas of the PacificOcean. In the U.S. alone, thesetsunamis killed hundreds ofpeople and caused many tens ofmillions of dollars in damage.Recent events in Papua NewGuinea (1998) and elsewhere arereminders that a catastrophictsunami could strike U.S. coastsat any time. The USGS, workingclosely with NOAA and otherpartners in the National TsunamiHazard Mitigation Program, ishelping to reduce losses fromtsunamis through increased haz-ard assessment and improvedreal-time warning systems.

I

U.S. Department of the InteriorU.S. Geological Survey

USGS Fact Sheet 150-002000

Helping Coastal Communities at Risk from Tsunamis—The Role of U.S. Geological Survey Research

REDUCING THE RISK FROM COASTAL GEOLOGIC HAZARDS

n 1946, 1960, and 1964, majortsunamis (giant sea waves

Aftermath of the 1960Chilean tsunami inHilo, Hawaii, wherethe tsunami caused61 deaths (photocourtesy PacificTsunami Museum).Inset shows damagefrom a local tsunamithat struck OkushiriIsland, Japan, in 1993(photo by DennisSigrist, InternationalTsunami InformationCenter). Floatingdebris, such as seenin these photographs,

Population pressures in the coastal zonesof the Pacific Ocean and the Caribbean areresulting in unprecedented shoreline devel-opment, putting residents, tourists, andproperty at increased risk from giant seawaves, called tsunamis. Tsunamis, often in-correctly referred to as “tidal waves,” can begenerated by distant earthquakes and by lo-cal seismic events, submarine landslides,and volcanic eruptions. For ocean-crossingtsunamis, there is often sufficient time toevacuate distant coastal areas, but moretimely and accurate real-time tsunami fore-casts are needed to avoid costly falsealarms. Local tsunamis generated byquakes on active seismic zones in Alaska,the Pacific Northwest, the Caribbean,California, and Hawaii can arrive atnearby shorelines in minutes. In thesecases, only better scientific understanding,informed disaster planning, and publiceducation will save lives in future tsunamis.

Protecting lives and property from tsuna-mis demands a clear understanding of howtsunamis are generated, the identification oflikely areas at risk, and mitigation effortsbased on public education. The NationalTsunami Hazard Mitigation Program(NTHMP), a partnership of the States ofAlaska, California, Hawaii, Oregon, andWashington and the Federal EmergencyManagement Agency, National Oceanic andAtmospheric Administration (NOAA), andU.S. Geological Survey (USGS), is cur-rently preparing tsunami inundation mapsand implementing mitigation plans forstates bordering the Pacific Ocean. TheNTHMP is also providing tsunami earlywarnings for these states by means of deep-ocean tsunami detectors and new seismicstations on land. The cooperation of Fed-eral and state agencies in the NTHMP isfurthering scientific understanding of tsu-nami hazards and facilitating the develop-ment of plans to prepare coastal commu-nities to better survive future tsunamis.

The mission of the USGS includes under-standing the geologic mechanisms, fre-quency, magnitude, and physical conse-

quences of natural hazards. In recent years,the USGS has upgraded its seismic net-works to provide NOAA’s tsunami warningcenters with detailed earthquake informa-tion to aid in timely notification of the pub-lic. The USGS and NOAA are currentlyproviding real-time seismic and tsunami in-formation to state offices of emergency ser-vices in Alaska, Washington, Oregon, Cali-fornia, and Hawaii.

To ensure that its efforts to reduce the riskfrom tsunamis are focused where they willbe most effective, the USGS convened atwo-day workshop in Seattle, Washington,in January 2000. This workshop was at-tended by scientists and managers from theUSGS, NOAA, state agencies, andacademia. Based on needs identified by theworkshop participants, the following recom-mendations on the role of the USGS in tsu-nami research were made:

Seismic networks—It is importantthat, as advances in technology and sci-ence allow, the USGS continue to enhanceand improve the quality and quantity ofseismic data supplied to tsunami warning

can causesignificantdestructionduringtsunamirunup.

Printed on recycled paper

centers. The USGS should also determinethe need for additional strong-motion seis-mic stations along U.S. coasts. Further, theUSGS should continue to develop softwarethat supports tsunami warnings for localearthquakes, particularly in Hawaii, Alaska,the Pacific Northwest, and the Caribbean.

Earthquake source characterization—In order to provide accurate warnings andhazard assessments, better characterizationsof critical earthquake source parameters areneeded. Modern methods of analyzing seis-mic data developed by the USGS can beused by tsunami warning centers in an over-all effort to improve the accuracy and timeli-ness of tsunami warnings. Further researchis also recommended into using rapid seis-mic inversion algorithms to estimate sea-floor displacement, an indicator of likelytsunami size, which could be automated aspart of local tsunami warning systems.

Hazard assessments—The NTHMP iscoordinating the preparation of tsunami in-undation maps for high-risk coastal commu-nities in Alaska, California, Hawaii, Oregon,and Washington. The USGS can providevaluable guidance in the preparation of thesemaps by analyzing and interpreting depositsfrom historic and prehistoric tsunamis to es-timate inundation limits, flow velocities, andrecurrence intervals.

Coastal bathymetry and topography—Producing reliable and useful inundationmaps for hazard assessment partially de-pends on accurate bathymetry and topogra-phy of coastal regions. The USGS, alongwith NOAA, NASA, and the Army Corps ofEngineers, have proven capability to surveycoastal and nearshore bathymetry and to-pography using modern techniques. It isrecommended that the USGS coordinate

with other Federal agencies to providesuch information for hazard mitigationplanning in high priority areas of the Pa-cific Northwest, Alaska, Hawaii, Califor-nia, and the Caribbean.

Sedimentary deposits as keys to tsu-nami character—Identification and in-terpretation of sedimentary deposits leftbehind by prehistoric tsunamis will im-prove our ability to assess the magnitudeof tsunami risk in areas with an insuffi-cient historical record. The USGS willprovide expertise and leadership in sedi-ment transport modeling to increase un-derstanding of the mechanics of sedimenttransport in tsunamis and of the depositsthey leave behind. Research would occurin field settings by integrating predictivemodeling with laboratory and post-eventstudies.

Post-event rapid response—The vis-ible effects of tsunamis are short-livedand may be lost after a single subsequentstorm or during clean-up efforts employ-ing earth-moving equipment. To deter-mine the effects of tsunami inundation onland, the run-up elevation and distance,flow-speed and direction indicators, andpatterns of sedimentary deposition mustbe mapped and quantified immediatelyfollowing an event. USGS scientistsshould join the International TsunamiSurvey Team, when warranted, to gatherinformation about tsunami deposits andto calibrate sediment transport models.

Tsunamis generated by landslidesand volcanic events—Landslides andvolcano flank failures in coastal and is-land settings have also initiated large tsu-namis. The accumulated knowledge ofUSGS scientists about submarine andcoastal landslides and active volcanicprocesses should be focused on improvingunderstanding of how and where these cata-strophic mass failures may occur. This in-

formation then can be used in regionalhazard assessments by Federal, state, andlocal authorities.

The efforts of USGS and other coopera-tors in the NTHMP are leading to a betterunderstanding of tsunamis and howcoastal populations can be prepared to sur-vive their onslaught. The work of USGSscientists in tsunami research is only partof the ongoing efforts of the USGS to pro-tect people’s lives and property from geo-logic and environmental hazards in thecoastal zones of the United States.

For more information contact:U.S. Geological Survey, MS-999

345 Middlefield RoadMenlo Park, CA 94025

(650) 329-5042http://walrus.wr.usgs.gov/tsunami

http://www.pmel.noaa.gov/tsunamiSee also Surviving a Tsunami—Lessons from Chile, Hawaii,

and Japan (USGS Circular 1187)This Fact Sheet and any updates to it are available on line at

http://geopubs.wr.usgs.gov/fact-sheet/fs150-00/

Eric L. Geist, Guy R. Gelfenbaum, Bruce E. Jaffe, andJane A. Reid

Graphic design bySusan Mayfield and Sara Boore

NATIONAL TSUNAMI HAZARD MITIGATION PROGRAMStates of Alaska, California, Hawaii,

Oregon, and WashingtonNational Oceanic and Atmospheric Administration

Federal Emergency Management AgencyU.S. Geological Survey

Computer simulation of a major nearshore earth-quake along the Cascadia Subduction Zone off thePacific Northwest shows the advancing wave frontsof the resultant tsunami.

Stuck area ruptures,releasing energyin an earthquake

Earthquake starts tsunami

A tsunami caused by an earthquake along asubduction zone happens when the leading edgeof the overriding tectonic plate breaks free andsprings seaward, displacing the sea floor and thewater above it. The arrival time and severity of thetsunami can best be predicted using complexearthquake parameters, such as accurate depthdetermination, focal mechanism, and high-resolution sea-floor displacement patterns.

Waves of the cata-strophic 1998 PapuaNew Guinea tsu-nami were up to 50feet (15 meters) highand, as can be seenby the devastatedforest in this photograph, inundated areas as muchas half a mile (800 meters) inland. This locally gener-ated tsunami, caused by a magnitude 7.1 earthquakejust offshore, killed at least 2,000 people and leftmore than 10,000 others homeless. Inset shows sandand debris left behind by this tsunami. Sand depositsfrom recent and prehistoric tsunamis yield informa-tion about the magnitude, extent, and frequency ofpast tsunamis, which can in turn be used to estimatethe hazard posed to an area by future tsunamis.

ColumbiaRiver