In reply to our earlier post about a Cascadia Subduction Zone (CSZ) event, many of you had questions about the impact of a CSZ event on Columbia Generating Station (CGS), the nuclear power plant at the Hanford site, and in Walla Walla County.
We reviewed the anticipated estimated impacts to eastern Washington using the Washington State Seismic Hazards Catalog on the DNR website. While the study stops just short of the Tri-Cities, the catalog does indicate that the shaking intensity would be a 5 on the Modified Mercalli Intensity (MMI) scale. However, CGS is located on the edge of 5 MMI (Moderate) and 4 MMI (Light). The best comparison that we could find shows that a MMI IV is comparable to a Magnitude 4.0 – 5.0 on the Richter scale. A MMI V is comparable to a Magnitude 5.0 on the Richter Scale. Either way, the impacts to CGS would be well within the design basis that the power plant was designed to withstand.
As for Walla Walla County, as shown on the Cascadia M9 Scenario Map we can expect to feel a CSZ event. The further you are to the east of the westcoast, the less it would be felt. Therefore, we’d experience a lesser magnitude event than would be experienced at the Hanford Site since we are slightly further east than Hanford. The worst case CSZ scenario is a quake lasting five minutes or longer. Regardless of the magnitude felt here, five minutes of shaking is a long time. We cannot rule out failure of brick facades, chimneys and the like. And consideration must be given for the amount of infrastructure damage the west side of the state will experence. Preparing is always a good idea, no matter what scenario you are preparing for.
Learn more about building a kit at: https://www.ready.gov/kit
View the Washington State Seismic Hazards Catalog at: https://fortress.wa.gov/…/prot…/seismicscenarios/index.html…
Learn about the differences between Mercalli Scale and Richter Scale at: http://www.diffen.com/diffe…/Mercalli_Scale_vs_Richter_Scale
According to the CSZ M9 scenario map, the shaking in Benton and Yakima counties would also be at the MMI V level, slightly more than what Walla Walla would feel. This level is described as “Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned.”