Wednesday, January 22, 2014

Vancouver amplification doesn't mean much


Wow, I never saw an earthquake paper get so much press!  Must be a slow month.  This issue really is esoteric in the extreme.  Although all the press is getting it mucked up, we are talking about a rock basin.  Any soft stuff on top is icing on the cake.  :)

The rock basin is hard cheese on a granite slab.  No jello.  Now, there are magnificent sediment deposits around there, but that's another issue.

The rock basin thing doesn't rise above the uncertainty fuzz of where the next earthquake will be when it hits.  We have the Big One way out in ocean, but my favourite is an M7 right under the city, a la Kobe.  This will literally throw the soft sediments.  All the big towers are most likely on a firm foundation, there are no raft foundations here, like in Boston (I hope).

So, if you want a potential damage map of the area, just look at the geotechnical records and guess what is under each building.  An old brick building on soft soil?  - Big Fail.  A 70's concrete building on a soft-soil raft foundation?  - Big Fail.  Bank Tower on rock?  - Laughing.

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