Tsunami deposit exposed in estuary bank
Dead tree from subsidence cause by the great 1700 quake.
There is so much to learn from the most recent earthquake in Japan. Certainly nuclear fission reactor design and operators are having a learning experience. Not one that could be called remotely pleasant and alas for some very dangerous with signs that the reactor containment may be partially compromised at last update. The policy implications for this will be interesting to follow and global.
In my own mind I have been developing comparisons between Washington State and northern Japan in terms of how does this seismic event relates to western Washington's tectonic situation. It is worth making some comparisons regarding the event in
Washington and are fairly similar. Both Japan Japan and Washington are located on a convergent plate boundary with ocean floor plate subducting under Japan and the same in . The major tectonic structure is essentially a major thrust fault with the ocean floor sliding under Washington Japan and . These types of plate boundaries produce the biggest earthquakes. How are they different? The ocean plate subducting under Washington Washington is much younger than the ocean plate subducting under . This might make a bit of difference as to where earthquakes take place and how deep earthquakes will be but only in a general way. There are likely some secondary effects and seismic events within the subducting ocean plate and overriding continental plate due to this age of crust difference, but again those are details for seismic geologists and the story of a big subduction quake is the same. Japan
Perhaps the biggest question for Washington State is the possibility of a major subduction quake located off shore or the possibility that the quake might take place beneath the land area along the coast. Distance to epicenters matter greatly. This last event in Japan was 80 kilometers off shore. It was a huge quake but at least some distance separated the quake from cities and homes. I have not read of any coastal subsidence or uplift along the coast of Japan from this event and am very interested if that took place. On Washington State's outer coast large quakes causing substantial coastal subsidence is evident all along the coast. Location and depth of quake epicenters matters greatly and this question is one of great interest for seismic folks.
The ocean plate subducting under Washington State is subducting at an angle such that lateral forces on the upper crust come into play. This is the case in parts of Japan as well, but in other areas the collision is more direct. In areas where the collision is at an angle there are strike slip faults, normal faults and blind thrust faults inland from the subduction fault and that is the case in Washington and in certain areas of Japan. At a localized level these faults are just as dangerous or depending on proximity substantially more dangerous. A major off set along the faults cutting across Bainbrige Island will give nearby land a jolt much greater than the subduction zone quake.
The bottom line is that there is plenty of evidence that Washington State will have similar types of large earthquakes that have impacted Japan and in fact these types of quakes should be expected and planned for in Washington State.
The tsunami impact in Japan is simply shocking. We know that tsunamis associated with great quakes have impacted the Washington coast. It is abundantly clear that large swaths of coastal lowland areas particularly on the outer coast are very vulnerable. This information is not new. First Nations peoples on the outer coast had many stories of a great wave. The last large quake in Washington State took place in 1700. Furthermore the images from Indonesia and Chile have previously reinforced the understanding of the risk facing Washington State as well as Oregon and British Columbia. But with the images from Japan, a country that has known tsunamis for centuries and even measured and recorded and planned for tsunamis, Washington State should learn some lessons.
Some steps for tsunami planning have begun. For example some state money was set aside for construction of tsunami shelters on the Long Beach Peninsula due to lack of natural safe locations being near by. Maps showing potential tsunami inundation have been developed based modeling the big quake. A careful look at what happened in Japan suggests that for areas without nearby safe high ground much more should be done. Warning systems have been built and signs pointing the way for escape have been installed. I am not sure of the status of the shelters on Long Beach, but it is abundantly clear that they are needed and there are likely other locations where these facilities will be needed as well.
In one very important regard, Washington State has a distinct advantage over Japan. At this point in time a lot less people live in potential tsunami hazard areas in Washington State than in Japan. Substantial changes will be required in land use planning and infrastructure investment to prevent substantial increases in population within tsunami areas.
From a land use planning perspective, all coastal counties and counties within the inland water areas should recognize tsunami areas as geologic hazard areas within existing critical areas ordinances that are required under the Washington State Growth Management Act. Clear guidance for recognizing this hazard and requirements for areas within this hazard should be developed by the State and the State needs to require that regulations for these areas are adopted and enforced at the local city and county level. Recognition of various circumstances will need to be considered. For example, towns have developed within the hazard area already. Oysterville and other small communities on the far outer coast will do very poorly when the tsunami arrives shortly after the great quake. Even small cities such as Aberdeen and Hoquium should have carefully thought through regulations and plans that require recognition and planning for a very destructive tsunami event that will happen.
A somewhat similar approach has been followed by counties in Washington State regarding volcanic hazards. However, because of a lack of specific state requirements some communities have developed geologic hazard regulations that are silent on the volcanic risk or have code language that will allow far too much development to extend into locations that will be destroyed. I an not advocating banning all development, but consideration of development scale and types should be considered and a rationale should be developed as to what will be allowed and what won't be allowed. I will give one example. Whatcom County has a volcanic hazard area and certain types of development are banned within those areas and policies for planning have been developed that recognize that these areas are at risk and development in these areas should be limited.
While arguments can be made about recurrence intervals of large scale volcanic or tsunami events not warranting any additional precautions or regulations, those arguments should be made only after watching a few videos of the tsunamis that swept inland along the Japanese coast last week.
A final policy issue is where infrastructure investment takes place. Clear state policies as well as local and federal policies should discourage investments that encourage development in dangerous tsunami hazard areas unless there are specific compelling reasons for the development with few alternatives such as shipping facilities.
People get ready. We do not want to leave people bewildered and confused on a dark winter night like the First Nations coastal communities in 1700.