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
really bedrock.

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 _ 
> (  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  
> pipe.      
>    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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