What Would a Tsunami do to Tacoma? Dnr Map Shows Possible Scenario

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Japan’s tsunami and earthquake drew the world’s attention last month and the interest spread to DNR’s Ear to the Ground blog. Interestingly, one of our most viewed articles last month concerning earthquakes and tsunamis was one we posted in January, weeks before the 9.0 magnitude quake hit in March.

Here, in order, are the top 10 most-viewed postings on Ear to the Ground last month:

DNR’s Division Geology and Earth Resources works with federal agencies to produce maps like this for local emergency planners.

The map, produced by DNR and the National Oceanic and Atmospheric Administration (NOAA), looks at various scenarios that could generate a tsunami in Puget Sound. Portions of the Tacoma tideflats –  port and industrial areas mainly but not many homes – could be under 6 feet of water or more if a 7.3 earthquake hit the Seattle fault. This occurence happens about once in 2,500 years. The last large quake on that fault about 1,000 years ago.

The Tacoma map and others in the series were funded by federal grants through the National Weather Service. Federal funds also help pay for DNR’s mapping of tsunami escape routes in low-lying coastal areas of Washington state. DNR and NOAA have produced tsunami threat maps of SeattlePort Townsend and other areas of the state.

There may be lots more of Puget Sound that supports or can support eelgrass, a critical habitat that salmon, sand lance, herring and other species use at various stages of their lives. Eelgrass is seen as a very important component of this marine system—and more is definitely better.

The new study by scientists in the ‘Nearshore Habitat Program’ at DNR explores the potential for the recovery of eelgrass in greater Puget Sound.

The study estimates the total area in Puget Sound within the eelgrass depth range, based on existing depth (bathymetry) data, and compares that estimate to current estimates of areas that have an abundance of eelgrass. Not all areas in this depth range can support eelgrass—for example, rocky shorelines will not support eelgrass.

However, the study—Area of Eelgrass Depth Bands in Greater Puget Sound—found that the total area within the eelgrass depth range is substantially larger than the recovery target recently adopted by the Puget Sound Partnership, the state’s lead in coordinating the cleanup and restoration of Puget Sound by 2020. 

This suggests that additional areas are available for eelgrass expansion—both through an increase in eelgrass coverage within its current depth range and through expansion of the depth range of eelgrass in response to changes in environmental factors—the most important of which is improved water quality.

3D computer image of depth data at Salmon Bank off San Juan Island.  A large eelgrass depth range area is indicated by the thin white line.

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