Friday, May 17, 2013

Toronto Earthquake a Washout

Looking at all the news I think this earthquake is more like the USGS M4.4 and not an M5.2.  It certainly wasn't as big as the last one!

The local effects of an earthquake are determined by the peak ground velocity (PGV) measured on the spot.  This can be derived from the seismometers we have all over Ontario, but probably won't be done soon, unless I pester people.  You can definitely feel about 0.5 mm/sec.  But damage needs about 500 mm/s.  Soft ground will amplify about 10 times.  A soft-story condo on soft ground will go to 100!

This was not felt on our ground floor on firm ground, so I am guess a general PGV of 0.3 mm/s, since I felt it very lightly on the second floor, which probably amplifies by 2.  Again, I think we are a factor of 2 to 3 below the last panic.

A real earthquake under Hamilton will produce 5 cm/s on rock, and huge amplifications elsewhere.  The odds are the same as other places, so it is best not to ignore it.  We in Ontario are exemplary in totally ignoring earthquake issues.  

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