reply to post by zenius
Glad someone else thinks so, I think we have been missing something all along. The Lyttelton quake brought it to my attention.
The Geonet site has always had the readings, I just didn't understand what it meant.
If you go to any quake on the Geonet Recent Quakes Page and click on Felt Reports, when the map comes up you can select 3 choices from the dropdown
list. If you pick PGV it shows the peak ground velocity from stations around the area. Obviously the highest reading will be the closest in normal
cases, although I seen one yesterday off Cape Runaway, East Cape that it was the 4th or 5th furthest away recorder had the highest velocity.
I found this pdf about velocity and as it happens that guy Thomas Heaton on the radio was a co author, so it must be his speciality
Its heavy reading, and I don't understand most of it but this caught my eye,
So it is tied in with the Modified Mercelli Intensity Scale (MM) anyway, but from my understanding it allows the siesmologists to detrmine the
intensity quickly, without depending on people sending in their Felt Reports.
It seems every location will react differently because of the geology, so what that means is you just can't compare a 6.3 in Christchurch with a 6.3
in lets say Arkansas. But you can compare velocity as cm/sec is the same anywhere on Earth.
In laymans terms I think cm/sec means how far the ground moved in one second. Being in the building industry I'm used to using millimeters, so when I
seen 70cm I didn't think too much of it, but thats 700mm or close to 3/4 metre, no wonder all those buildings fell down in Christchurch!
edit: looking at the Geonet Shaking Map with PGV on for the Lyttelton quake
doesn't show much, only one station close by, at Oxford, and the reading there is quite low at 1.4235cm/s, but using th USGS readings at 70cm/sec the
MM should have been IX not VIII
MM 8: Heavily damaging
Alarm may approach panic. A few buildings are damaged and some weak buildings are destroyed.
MM 9: Destructive
Some buildings are damaged and many weak buildings are destroyed.
MMIX (9) better describes what happened I think.
edit on 28-2-2011 by muzzy because: (no reason given)