PSN-L Email List Message
Subject: Re: Shaking house
From: "GMV" gmvoeth@...........
Date: Tue, 17 Feb 2009 16:03:51 -0700
Just A thought;
I think I heard reference to bedrock
and on bedrock is exactly where you
want to be.
just a thought;
Id consider hacking/blasting/jack hammering a little
nook or cranny into the side of bedrock if it is
I understand its better than underground
for seismic quiet.
its like 800 feet straight down to bedrock
where I live.
----- Original Message -----
Sent: Monday, February 16, 2009 5:41 PM
Subject: Re: Shaking house
> In a message dated 16/02/2009, rog@.......... writes:
> I am a novice and building up a vertical-type seismometer, but live in a
> wood frame house with a crawl space that shakes considerably with doors
> closing and the washing machine going, etc.
> Hi Robert,
> Can you describe your house and the setup in more detail, please? What
> are the dimensions of the crawl space, the location of the seismometer, the
> composition of the ground, the ground slope around the house and the depth of
> the water table?
> You will not be able to get a low noise seismic signal if the
> seismometer is supported by a wooden building. Mounting the seismometer on the ground
> well away from the outer walls usually reduces any noise from the building.
> It is usual to provide a concrete block on which to mount the
> seismometer and a suitable draftproof + insulation cover, which may be made from 2"
> Celotex. You can dig a shallow pit and cast a 50:50 sand and cement plinth.
> Don't use any gravel. First lay 1" sand and two sheets of damp proof polythene in
> the bottom of the pit and fold up the corners to above ground level. Staple
> / tape the top of the folds. Then use a wood surround mould. If you need more
> height, dig a deeper pit with sloping sides and surround the plinth with
> cast concrete walls. You leave the plinth covered and wet for up to 4 weeks to
> allow the cement to cure fully. Then you can dry it out. I stick SS mounting
> disks to dry concrete with two component acrylic cement.
> The house wiring and Earth connection should provide significant
> shielding and protection from lightning.
> Is it possible to locate the seismometer outside?
> Certainly, but you need to build a watertight housing for it. Have a
> look at _http://www.guralp.com/articles/20040400-casestudy-eskdalemuir/support_
> (http://www.guralp.com/articles/20040400-casestudy-eskdalemuir/support) You
> will get lower noise if you make the top nearly flush with the ground / put a
> vertical bar fence around the site. Maybe wood + wire paling? You may need to
> consider possible problems with high rainfall and flooding.
> What is the easiest way to run a long cable? I do have massive bedrock
> on the property about 300 ft from the house.
> A 300 ft cable run will very likely require you to provide lightning
> protection, but this depends on the location. A lot of the US has poor ground
> conduction and / or a deep water table. Check on the local advice? You can buy
> power cable with spiral steel wire reinforcing and extra insulation so that it
> can be laid directly in a trench. This protects it from ground movements, but
> it won't be cheap. Otherwise you can lay ordinary cable in polythene water
> The difficulty is in threading the cable through the pipe. It has a very
> high total friction. If you have a suitable quarry, cliff, bridge,
> stairwell, or tower, you can hang the pipe vertically and feed the cable in from the
> top. Otherwise you need a smooth iron rod and a strong magnet. You use this to
> pull a cotton or similar strong string through the pipe, then a strong cord
> and then the cable. You can put talc powder in the pipe to lubricate it. Suck
> the powder through first with a vacuum cleaner? You can also use Molybdenum
> Disulphide or Graphite powder, but they are both messy.
> Hope that this helps,
> Chris Chapman
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