Steve Rooke wrote:
Well, Steve has been experiencing a LOT of after-shocks, some of which
are still big enough to move things around and I found I had to grab
hold of my cup of tea to stop it shaking onto the floor last night. In
fact these after-shocks are still opening up new cracks in roads and
causing buildings to fall.
As for my height position, I have run a few surveys but I'm getting
varying readings and I wonder if the after-shocks are messing up the
survey results. The latest one which was during a fairly stable period
was 6.8 MSL.
The mast could have sunk a bit or even this whole area could have done
as I live on reclaimed marsh-land. My Mothers 3 year old house looks
like it has sunk a bit at one and and risen at the other, ie. it looks
like it has tipped slightly as her house is built on a concrete
pontoon.
You could easily have a displacement of a meter or more..
The (M7+) Landers earthquake here in Southern California a few years
back had a lateral displacement of 10 meters or so and vertical
displacements of a meter.
If there's any soil subsidence, that would also account for a lot
http://all-geo.org/highlyallochthonous/2010/09/tectonics-of-the-m7-earthquake-near-christchurch-new-zealand/
has a nifty picture: the classic aerial shot of a hedgerow/treeline with
obvious displacement (about halfway down the page)
"New Zealand geologists have already identified a 13km fault trace with
3-4 m of right lateral, strike-slip offset, and variable vertical
movement of up to 1 m. "
Also there was this in a page linked from the above:
Deformation
Portable GPS instruments are planned to be deployed on September 6
(Monday) to re-occupy GPS 40 - 50 sites in the region looking for
changes. GNS scientists will be joined by colleagues from Land
Information New Zealand (LINZ).
A preliminary estimate of the McQueen's Valley (MQZG) co-seismic
displacement is 135 mm at about 300 degrees azimuth. This permanent
receiver is located on Banks Peninsula. This result is consistent with a
magnitude 7.1 earthquake on a vertical strike-slip fault at the location
where the geologists have found surface rupture, but it is only one
point and it would be consistent with many other scenarios as well. We
can expect displacements of 200+ mm at a number of the temporary GPS
stations we are planning to visit, and there is one station in
particular that may be within a few kilometres of the surface rupture
and thus have a much higher displacement.
It wouldn't surprise me if they adjust the height of MSL but I would
have thought they would have moved it the other way in an attempt to
forestall fears of the effects of Global Warming.
Regards from Quake City,
Steve
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