First: Lyle alerted me to Callan's post on the AGU page regarding coastal subsidence along the west coast of Japan from the earthquake mountainbeltway/new-gps-vectors/. The critical part is that the Japan quake matches reasonably well with the evidence Brian Atwater has found on Washington State's outer coast.
Second: I looked up one local critical areas code for our outer coast, Grays Harbor County. Tsunami is not in the definitions section and there is no mention of tsunamis in the geologic hazard section. There also is no mention of alluvial fan hazards. Nor is there mention of coastal subsidence or any other seismic hazard beyond reference to the designing building to meet the uniform building code. Grays Harbor does have flood regulations that take into account high water from the ocean utilizing FEMA flood maps, but the tsunami hazard dwarfs the 500 year flood levels and the FEMA flood maps make no mention of tsunamis.
Google Earth view of Grays Harbor County on Washington State's outer coast
Grays Harbor County is predominantly heavily forested low mountains and hills. Most of the populations lives on the coast, along the shores of Grays Harbor, the drowned lower valley of the Chehalis River, and along the Chehalis River valley. Evidence of past tsunamis can be observed at many coastal estuaries along the shoreline including the spectacular ghost forest along the Copalis River in the northern part of the county SEE HERE.
Most of the developed areas in Grays Harbor County developed well before there was any understanding of the seismic risk on the Washington State coast. Settlement by Europeans and Americans began in the early 1800s with settlement taking place along the inner shorelines of the bays. If local First Nations peoples said anything about giant waves, the stories may have been difficult to believe. As geologists began to understand plate tectonics and seismic events along convergent plate boundaries, the lack of earthquakes on the Washington coast became an interesting riddle. Brian Atwater postulated that there should be evidence of past quakes along the Washington coast and went to Grays Harbor County and found the evidence in the 1980s. Subsequent studies along the coasts of British Columbia and Oregon have built on our understanding of the seismic risk.
While Grays Harbor has yet to recognize tsunamis in the development regulations, the county emergency planners have been working hard to plan for the coming earthquake and tsunami event. The communities in Grays Harbor are well signed with tsunami evacuation route signs, tsunami warning sirens are more prominent than cell phone towers and there are routine community events. People in Grays Harbor are well aware of the risk.
In addition to evacuation routes, Grays Harbor County as well as areas to the south in Pacific County have begun thinking about tsunami platforms as some areas will be difficult to evacuate within the short time between the big quake and the tsunami arrival. Elevated areas within the dunes on the sand spits may provide enough height along with a deeply bedded platform to protect people. And the platforms may provide great views for birders and other tourists.
Tsnuami Platform. Photo courtesy ITC
Grays Harbor County has made great progress in emergency planning. People living there know what to expect and are as well prepared as anyone. But in terms of land-use planning within the county codes, tsunami hazards are note yet recognized. The Tsunami Hazard Map of the Southern Washington Coast (Walsh and others, 2000) http://www.dnr.wa.gov/Publications/ger_gm49_tsunami_hazard_southern_coast.zip closes with the following "This means that, while modeling can be a useful tool to guide evacuation planning, it is not sufficient resolution to be useful for land-use planning." Walsh and others note that horizontal errors of up to 165 feet and vertical areas on the order of 7 to 20 feet may be present in the model.
This problem with dead on accurate maps for planning purposes ought not to prevent some level of development planning. Look at the evacuation maps carefully and it should be noted that fire stations and police stations are located with the tsunami hazard area. Our federal, state and local governments invest large sums of money in public buildings. Land-use planning should at a minimum include the tsunami hazard risk for locating key government facilities as well as hospitals. And there is no reason not consider other types of development as well. Should nursing homes or child care facilities be developed with tsunami hazard zones? Circumstances will vary from community to community in how these difficult decisions should be made and how the risks posed will be dealt with. There is much to be learned from the Sendai, Japan earthquake and not only emergency planners but land-use planners should be looking closely at what worked and did not work in Japan. And we will never have dead on accurate maps of tsunamis, but we should have a pretty reasonable idea where the tsunami danger zones are based on the maps we have so far.
Great Britain Prime Minister David Cameron said of the quake in Japan "a terrible reminder of the the power of nature”. Too frequently events like this are viewed in that manner. From the perspective of living on the Cascadia subduction zone western Washington residents should be thinking this about the Japan quake “a terrible reminder of the cost of not planning well for an obvious risk.” From the dragging out the replacement of the Seattle viaduct to huge government subsidized development projects proposed within known tsunami hazard zones, Washington State and communities within Washington State are ignoring an obvious hazard at potential great cost in property, investment and lives.
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