Sunday, March 13, 2011

Oregon Tsunami Inundation Maps and Reports

They have had these maps for a while now, but they have been updating them based on new data. Here is one of the main sites for information:

Oregon Tsunami Clearinghouse
This site has all kinds of information. One of the links is to inundation maps:

The Tsunami Map Viewer returns a map of areas with Tsunami Evacuation Zones based on information that you enter.

The part where you enter an address, does not work for me. Below that is a search box labeled "Search By a Coastal Area". It has a drop down menu. Pick an area from the menu, and it will show you a map, with flood areas highlighted in yellow.

There are also options in the upper right corner of the map to show a satellite view or a hybrid map/satellite view. On the left is a nav-bar, you can move the map around and zoom in quite close to see photographic detail. A note in the sidebar explains:

Important Map Notes

The Oregon Department of Geology and Mineral Industries (DOGAMI), in partnership with NOAA, is developing new tsunami evacuation maps and revising current maps for the entire Oregon coast.

The anticipated date of completion of this project is 2013. The interactive map on this website depicts first generation evacuation maps developed between 1995 and 2006 that show evacuation zones in yellow based on the maximum inundation expected for a local Cascadia tsunami.

This maps on this website incorporate new information and technology gained since the 2004 Indian Ocean tsunami that have aided the development of a second generation of evacuation maps. The new maps depict the maximum extent of inundation expected for both distant tsunamis (orange) and a local Cascadia tsunamis (yellow).

Since the Japan earthquake, there have been people in the media claiming that a Cascadia quake would be very similar to the one in Japan. I believe the inundation maps are based on a 9 point richter scale quake on the Cascadia fault zone.

The map below I shows the Cascadia fault zone (It's not an inundation map; I found it on another website. Here, the yellow just marks the fault zone):

There hasn't been a large subduction zone quake in Oregon since 1700, or so geologists tell us. They also say that at that time a 10 foot wall of mud and water washed inland over low lying areas. They base their guess on fossilized remains of Indian settlements that were buried under a layer of mud in that time period (sorry, I didn't save the link). How accurate their estimate is, I couldn't say. A 10ft wave, while serious, isn't the 33 ft waves Japan had just had.

In general, there are not many quakes in Oregon. I've lived here since 2004 and have not even felt one. But they do happen occasionally. Mostly they are small, with a few exceptions.

Because Oregon is not as seismically active as Japan, I don't know how apt the comparison is. But does the lack of earthquakes here make us complacent? Perhaps.

So just how serious is the potential threat?

Earthquakes in Oregon State
[...] There are numerous fault zones in Oregon. A graphical representation is available from the University of Oregon. The information below about earthquake hazards in Oregon is exerpted from an FAQ by the Oregon Department of Geology and Mineral Industries.

Q: Is there an earthquake hazard in Oregon?

A: YES! There have been no “big” earthquakes in Oregon’s brief history, and there is no question that damaging earthquakes have been far less frequent in Oregon than in California or Washington. However, geologic research tells scientists that Oregon will some day experience big earthquakes, and the Scotts Mills earthquake of March 25, 1993, and the Klamath Falls earthquake of September 20, 1993, confirm the research. Because we are poorly prepared, the damage could be great. We are faced with a small chance of a great disaster.

Q: What about “The Big One”?

A: Geologic research in the last few years has shown that Oregon and Washington have probably been shaken by numerous subduction zone earthquakes during the last several thousand years. Subduction zone earthquakes occur when two great crustal plates slide past each other beneath the coast of Oregon and Washington. These earthquakes occur, on average, every 300-600 years, and the most recent was about 300 years ago. The subduction zone earthquakes were probably centered just off the coast of Oregon and Washington and may have been as large as magnitude 8 to magnitude 9. Such earthquakes would cause significant shaking and damage in much of western Oregon. Scientists cannot predict whether the next such event might occur in two years or 200 years.

Q: What parts of western Oregon are most dangerous?

A: Local earthquakes are most common in the Portland metropolitan area, northern Willamette Valley, and Klamath Falls area and may threaten the coast from Coos Bay south to Brookings. We simply do not know about the risk of local earthquakes in most other parts of Western Oregon. All of Oregon west of the Cascades is at risk from subduction-zone earthquakes. The amount of earthquake damage at any place will depend on its distance from the epicenter, local soil conditions, and types of construction.

Q: What about faults?

Two of the largest earthquakes in Oregon occurred in 1910 and 1993. The 1910 earthquake was the largest historical shock within the state’s boundaries at a magnitude of 6.8, but it occurred too far offshore to cause damage, whereas the damaging 1993 earthquake was the largest historical earthquake beneath the land area of Oregon, with a magnitude of 5.9. [...]

There are so many variables. And a great deal of uncertainty. Perhaps the best we can do is to be prepared for the worst, and hope for the best. At any rate, preparation can help minimize the damage and enhance the recovery, whatever the size and scope of an event, whenever it may happen.

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