The final presentation for Saturday was by John Schelling of the Washington State Emergency Management Division and Tim Walsh of the Washington Division of Geology and Earth Resources of the Department of Natural Resources, and was titled "A Review of the Honshu 9.0 Earthquake and Tsunami, and Potential for a Similar Event in the Pacific Northwest", although they were simply calling it "Can It Happen Hare?"
I won't go deeply into the historical precedents, or rehash the recent Tohoku earthquake on Honshu, or the recent Chile or Indonesian quakes. For now, here are some points I can pull from my notes; I'll look up references and refine/add to this later.
- The Tohoku earthquake was the fourth largest in recorded history.
- The "rupture" was 500 kilometers long, the entire length of the subduction zone.
- The tsunami reached the fourth and fifth floors of buildings.
The entire coast of Japan is dotted with monuments saying "Don't build below here"; where these warnings were heeded, destruction was minimal.
- The area hit was approximately the size of Washington's Olympic Peninsula.
- The ground shifted approximately 10 feet to the east, and dropped ("subsided") three feet.
- The magnitude--wrong word?--of a tsunami depends on how much water is displaced. Seems obvious, in retrospect...
- If the ocean floor subsides, then the tsunami will be preceded by the water "rushing out to sea." This is known in the industry as a "clue." See Hilo, 1946.
- An earthquake will be followed by multiple tsunamis; the major damage is often by later waves. (Either later waves are bigger, or things calm down and folks go to clean up or look for "stuff".
- The Cascadian Subduction Zone is approximately 500 km long, just like the one that caused the Tohoku quake. (Which explains our interest.)
- A tsunami in Washington State from the Cascadian Subduction Zone is expected to arrive in approximately 25-30 minutes, have 30 foot wave heights, and a 6 foot ground subsidance.
***I had heard that National Geographic television had a very good special on the subject of the Tohoku earthquake; when I got home fro the Salt Mines today I turned on the TV and, after switching to my usual Satellite Radio channel--40s Swing and Big Band--I scrolled through the guide to see what else was on, and saw that I was just in time to catch NatGeo's Witness: Disaster in Japan.
Very little narrative or explanation, all video shot on-site, much of that with camcorders or cell phones. The web site (link above) has pics and video, as well as other info.
Schedule shows that it will run again Sunday April 24, at 0800.
Highly recommended. Available on iTunes, if you are so inclined.
***Not to be outdone, the Discovery Channel is premiering MegaQuake: Hour That Shook Japan on April 24th at 10 PM ET/PT.
Experience Japan's earthquake and tsunami through new footage and first person accounts. Understand the mega-physics inside this latest Ring of Fire cataclysm that rocked the Earth on its axis. Scientists explore whether the Pacific NW U.S. could be next.