Tsunami Hazards in Cascadia : by Timothy J. Walsh Washington Department of Natural ResourcesDivision of Geology and Earth Resources Partners in Emergency Preparedness April 27, 2011
•On April 1, 1946, amagnitude 8.0 (Mw)earthquake with thesource in theAleutian Islands tothe south of UnimakIsland generated atsunami thatdestroyed this five-story lighthouse,located 9.8 m abovesea level.
•Only thefoundation andpart of theconcrete sea wallremained. All fiveoccupants werekilled. The wavesdeposited debrisas high as 35 mabove the sea.Although littledamage occurredin Alaska, exceptat Scotch Cap, thetsunami was oneof the mostdestructive ever tooccur in theHawaiian Islands.Photo credit: U.S.
The school children noted that the water had receded
Across what hadbeen the playingfields is themonument to thevictims
•At least 24 people were killed here, many of whom were childrenplaying by the waterfront. The tragedy of the 1946 tsunamiprompted the U.S. Coast and Geodetic Survey to establish theTsunami Warning System
Abridged fromSeismicity of theUnited States,1568-1989(Revised), byCarl W. Stoverand Jerry L.Coffman, U.S.GeologicalSurveyProfessionalPaper 1527,United StatesGovernmentPrinting Office,Washington:1993. Prince William Sound, Alaska 1964 March 28 03:36:14 UTC (March 27 local) Magnitude 9.2
Valdez sits on the edge of an outwash delta 150 km from the epicenter. Duringthe shaking, the unstable, saturated material failed. A slice of the delta, 1,220m long and 183 m wide, slid into the sea, carrying the docks and part of thetown with it. The slide generated a wave which slammed the waterfront 2 to 3minutes after the onset of the quake. The wave demolished the rest of thewaterfront, destroyed the fishing fleet, and reached 2 blocks into town, killing 30people
Tsunami damage from the Highway 109 bridge over 1964 Alaska earthquake Copalis River The wave here was about 10-12 feet. Highway 109 bridgeHouse torn apart over Joe Creekat Pacific Beach
This earthquake also generated a Pacific Ocean-wide tsunami that killed 110people, 8 here in Crescent City, CA. Note fire in background. This event led tothe opening of a second tsunami warning center in Palmer, Alaska.
1993OkushiriIslandA view of tsunami and related fire damage on southeast OkushiriIsland in the community of Aonae. Photo orientation is lookingnortheast. Numerous fires broke out following the tsunami, addingto the property loss and misery. More than 120 people were killedin Japan (Okushiri and Hokkaido Islands) by the tsunami.
On the west side of Okushiri Island many locations experienced a maximum runup ofover 20 m. This small valley leading to the ocean experienced a spectacular runup of 31m. Note the debris in the foreground, including a broken steel reinforced concrete utilitypole. Discolored and dead plants and grasses are evident on the hillside. This well-studied earthquake and tsunami led to significant advances in modeling tsunamis.
Placer River Silt Earthquake-induced ground crackDrowned forest in Girdwood, Alaska, killed in 1964 A.D. 1700 Ground surface 1,100 year old ground surface from Brian AtwaterDrowned forest along the Copalis River,Washington, killed in A.D. 1700
Right, subsided marshalong the Niawiakum River, Tsunami sandssouthwest Washington.Below, note pitfalls ofworking in tidal marshes. A.D. 1700 ground surface
The realization that Cascadia was active was instrumental to the creation ofthe National Tsunami Hazard Mitigation Program, which develops tsunamiinundation maps for vulnerable coastlines. These are based on a combinationof numerical modeling, and , where possible, paleoseismology.
The modelcalculatesthe watersurfaceelevationand velocityat each gridpoint
Tsunami parade at Hiro. Storm surge trace REMEMBER THE PASTTsunami monument from Nobuo Shuto
A TRAGEDY OF FOREIGN TOURIST WHO COULD NOT UNDERSTAND WARNING Her last position from Nobuo Shuto
Washington has a limited historical record, so we rely onmodeling to establish tsunami hazard zones
A tsunami generated by a Cascadiasubduction zone earthquake willarrive in less than 45 minutes. Forthese events, as was the case inBanda Aceh, the earthquake must bethe warning. Citizens must knowwhere to evacuate from and where toevacuate to, and must do so quicklyand on foot.Note the long peninsulas or spits oflow-lying ground. Ocean Shorespeninsula is 7 miles long and LongBeach peninsula is 20 miles long withlittle or no high ground over thosedistances. For these areas, tsunamidefenses are appropriate.
After TWO BUILDINGS IN AONAE, 1993 DuringBefore （北海道新聞社） from Nobuo Shuto
THE TWO BUILDINGS THAT REMAINED. Tsunami traceThis building stopped a house and boats.
Those two buildingsand other Japanesetsunami defensestructures formedthe basis of a studyof buildings thatsurviveddevastatingtsunamis wheneverything else inthe area wasdestroyed.
DEFENCE STRUCTURESSEA WALLSTSUNAMI BREAKWATERSTSUNAMI GATEHIGHTENING OF RIVER DIKES from Nobuo Shuto
At Minami-Sanriku town,an apartmentbuilding wassituated rightnext to thecoast anddesignated asan evacuationbuilding asshown byevacuationsigns, but therewere tracesthat tsunamialso hadreached the 4thfloor.
This three-storybuilding (below) wasthe disastermanagement centerof the town whichwas also designedto function as atsunami evacuationbuilding. At the timeof tsunami, aboutthirty municipalofficials evacuatedto the rooftop butonly ten of themsurvived. A youngfemale official whokept deliveringevacuation messageto the villagers untilthe last moment hasnot been found yet.
We formed a partnershipwith FEMA and theApplied TechnologyCouncil to providebuilding code styleguidance for buildingfacilities to withstand amagnitude 9 earthquakeand be suitable forvertical evacuation.Planning for the right sizeearthquake is critical.
Project Safe Haven: Tsunami Vertical EvacuationLong Beach Peninsula/Pacific County
Safe Haven Options (from FEMA 646):Towers –• Limited Space• Blocks Views• Few Options for ShelterBuildings –• Expensive • Better get it right the first time!• Very Large, Likely to Block Views• May require Private Development • Incentives for Height?Berms –• Least Expensive Option• Can be Multi-Purpose• May be Placed to Limit View Blocking
Vertical Evacuation Safe Haven Project • Community-based, ‘bottom-up’ approach • All options (buildings, towers, berms, etc.) are on the table for consideration Common Themes: • School Safety • Seniors and special needs populations • More conservative travel times