Thursday, September 29, 2011

The Seattle amplifying basin


Yeah John Vidale!  John doesn't participate in our g+ seismic silliness because he is quoted in practically every news article on earthquakes and has to stay serious.  :(

Anyway, double basins are fun as shown with the Mexico earthquake.  You can have your soft sediments on top, which amplify PGV by a factor of ten.  This is enough to destroy most cities.  But a deep basin can jump things up by another factor of 10!  Thus, you get hit with a double whammy of a factor of 100!

This is what will crumble Seattle when the 'Big One' hits, just like Mexico.  I can't see Vancouver in this situation.  A subduction earthquake can't put out more than 10 cm/s, like Japan, unless you are right on top of it, like Chile.  I estimate this is what hit the coast of Mexico during that quake.  The region around Mexico City only measured about 1 cm/s on firm ground.  The basin knocked it up to 10 cm/s and the soil to 100 cm/s.  Seattle will be much worse, but after 100 cm/s you can't measure anything! and it really doesn't matter.

Over 100 cm/s, eyewitness reports tell of visible standing waves that march across the basin like tornadoes, destroying everything.  Things get thrown into the air.  etc, etc.

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