Earthquakes
earthquake |ˈərθˌkwāk| noun a sudden and violent shaking of the ground, sometimes causing great destruction, as a result of movements within the earth's crust or volcanic action.

Oregon Quake Prep Seminar Sep 22, 2010
The purpose of this training was to Train the Outreach Coordinator while providing a consistent message, statewide, through George Priest’s Cascadia Subduction Zone Earthquake presentation.

A new catch phrase was coined – Earthquake Ready, as the highest state of readiness.

George Priest emphasized a high probability of this earthquake occurring within one’s lifetime and very certainly occurring during one’s grandchildren’s lifetime.

The earthquake can best be visualized as a zipper unzipping. An earthquake with magnitude 8.2 would involve the southern portion of the CSZ – unzipping a length of about 300 miles during a 3-5 minute period. An earthquake with magnitude 9.2 would involve the entire 600 mile length of the CSZ during a 6-10 minute period.

The “Shake Intensity” felt at any specific location would be virtually the same for the 8.2 and 9.2 scenarios even with 30 times more energy being released during the 9.2 scenario. The difference being the length of time during which buildings and infrastructure would be subjected to the intense shaking.

The average frequency of occurrence for these gargantuan CSZ earthquakes, along the Southern Oregon Coast (Brookings), calculates to once every 220 years. For Newport, it calculates to once every 350 years. At the north end of the CSZ (Vancouver, BC), the frequency of occurrence calculates to once every 500 years.

The last rupture of the CSZ having occurred in January 1700, means Oregon is overdue for a major earthquake. Governmental officials are seeking to raise citizen awareness and have scheduled major exercises, the first of which involves Lane County (Drop, Cover and Hold), on January 26, 2011. A Statewide exercise is planned for 2012. These exercises are being patterned after California’s exercises which are currently in progress.

George Priest suggested the recent Chilean earthquake, magnitude 8.8, was what he is expecting for Oregon. He advised that the Chilean landmass jump to the west, of 25’ while dropping 5’ of elevation, was not expected for the Oregon Coast. Approximately 60 miles of continental shelf sediments separate the “locked zone” from our shoreline. George believes these sediments will absorb most of the horizontal and vertical displacement. The geological setting is different for Chili, where the coastline is almost directly over the “locked zone”. The expectation, for the Florence area, is a horizontal displacement of 6-10’ with a vertical drop of 1-2’.

The “dunal sand” sediments, in the Florence area, tend to amplify the “shake intensity” by 25%. This can be visualized as your child or grandchild turning up the volume by 25% from the already high volume that you were about to request be lowered.

George and others discussed the isolation, in small pockets, that coastal residents can expect as the norm. Landslides, bridge failures and blockage by fallen trees and power lines are projected to prevent travel by road. There was further discussion that a mandatory mass evacuation may be ordered from the Federal/State Level, after 2-3 weeks. Mobilizing the “Fishing Fleet” seemed to be the preferred method for evacuating coastal communities through the ports.

The “Lake Slosh Effect” was mentioned by George as currently being modeled to determine the level of inundation residents, living near inland lakes, could expect. One can visualize this by putting about an inch of water in a shallow pan. When one starts to move the pan, the water sloshes up one side then the other – demonstrating an inundation event which will be occurring immediately, during the intense shaking event.

When asked how long the Ocean Tsunami waves would last, George Priest answered, “They should last for 8-10 hours with the strongest occurring in the first 4-5 hours.

It is clear; the State’s emphasis has shifted to preparing its citizens to survive the earthquake, recognizing that a great deal of progress has been made in preparing the coastal communities to survive the associated Tsunami.