Thursday, September 23, 2010

Tabulated New Zealand Earthquake Strong Ground Motions


This is absolutely fantastic!  It shows the PGV and site class.  1 is solid rock, 4 is swamp.  This is a table of all the available accelerometers.  Nothing near the epicenter on firm ground, the nearest is at 84 km and gives 4 cm/s.  Something on swamp near the quake gives 40cm/s!  The nearest rock is 500 km away.

It's sad we won't learn too much about this quake.  For that you need accelerometers on rock quite close.  Then you can see how the rupture went, and if there was anything unusual, which I suspect.

For students, the main advice here is to be sure of your site when you plunk down an accelerometer.  It is best to do a noise survey, or note local drilling results (n-values).  The site classification from 1 to 4 is rather crude, but better than a kick in the head.  Try very hard to locate on something solid.  It can really pay off!


Anonymous said...


with a PGV of 40 cm/s on a swamp, what would the maximum lateral ground displacement actually be (I know i can figure it out with a little calculus but I'm too lazy)?

Harold Asmis said...

Look at the paper, I think it does this one with displacement.

Harold Asmis said...

Actually, the graph might be wrong, since all accelerograms are 'corrected' to eliminate displacement drift, since it is assumed the device must return to origin. In this case, they might be wrong, but you could only tell with a GPS monitor. I suspect there was a lot of shifting, and it would look nice with a Sat. Sar, like they did for Italy.