Friday, July 18, 2014

New US seismic hazard maps are probably useless


For the past 30 years there was an earthquake battle raging in Canada.  The seismologists (who can't do math) were fighting the engineers (who can't do physics).  The national building code devolves all the seismic stuff into a lateral body force coefficient.  It's sort of equivalent to tilting the building, or applying horizontal gravity.  Engineers love it because it is similar to wind load.

So every time the seismologists bumped up the map, the engineers would lower the coefficient, making everything exactly the same.  Now, the US will probably do the same.

The lack of both math and physics into this mess gives us a big problem.  PGV amplification on soft soils in a rock basin can be up to 100 times.  The acceleration doesn't amplify, since it all has to do with frequencies.  As with Chile, we are going to see a big mess if there is a significant earthquake in North America.  Then we will learn, la, la.  :)

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