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.  :)

Thursday, July 17, 2014

Europe is fine with Russia, lots of business as usual

They have accepted his apology for the latest aircraft shooting.

(Sorry, I made up the picture)

Alaska armpit M6.0

It's a shear earthquake, but the fault doesn't really line up.  There could be a lot of error since all the instruments are off in the main part of Alaska.  Anyway, once we have the M7.5 my prediction will be complete, although marked as late.  :)

Tuesday, July 15, 2014

Oklahoma gets hammered

Unusually strong ground motion for tension (normal) earthquake.

This was an M3.9 that knocked things off shelves.

Android screenshots are a bitch.

Monday, July 14, 2014

Oklahoma earthquakes: 7 in 1 blow!

I remember that fable where the guy killed 7 flies in one swat, and went on to say 7 giants in one blow.  In the same way the news is full of 7 earthquakes in one day.  The best one was the M4.3 along the shear zone.  It was an oblique shear with a thrust component.

That thrust aspect added some more juice to the ground motion, so that it was an Intensity IV, which is probably scary.

The ground motion map (there are absolutely no accelerometers here) is a classic thrust-shear combination.  The long aspect to the NE is the shear, with a little directivity to the north.  The higher intensity in the centre is the thrust.