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  
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





In a message dated 16/02/2009, rog@.......... writes:
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>I am a=20
  novice and building up a vertical-type seismometer, but live in a 
wood=
=20
  frame house with a crawl space that shakes considerably with doors 
clo=
sing=20
  and the washing machine going, etc.
Hi Robert,
 
    Can you describe your house and the setup in mo=
re=20
detail, please? What are the dimensions of the crawl space, the location of=20=
the=20
seismometer, the composition of the ground, the ground slope around the=
=20
house and the depth of the water table?
 
    You will not be able to get a low noise seismic=
=20
signal if the seismometer is supported by a wooden building. Mounting the=20
seismometer on the ground well away from the outer walls usually=20
reduces any noise from the building.  
    It is usual to provide a concrete block on whic=
h to=20
mount the seismometer and a suitable draftproof + insulation cover, which ma=
y be=20
made from 2" Celotex. You can dig a shallow pit and cast a 50:50 s=
and=20
and cement plinth. Don't use any gravel. First lay 1" sand and two sheets of=
=20
damp proof polythene in the bottom of the pit and fold up the corners t=
o=20
above ground level. Staple / tape the top of the folds. Then use a wood=
=20
surround mould. If you need more height, dig a deeper pit with sloping sides=
 and=20
surround the plinth with cast concrete walls. You leave the plinth covered a=
nd=20
wet for up to 4 weeks to allow the cement to cure fully. Then you can dry it=
=20
out. I stick SS mounting disks to dry concrete with two component acrylic=20
cement. 
    The house wiring and Earth connection should=20
provide significant shielding and protection from lightning.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>Is it=20
  possible to locate the seismometer outside?
    Certainly, but you need to build a watertight=20
housing for it. Have a look at http://www.guralp.com/articles/20040400-casestudy-eskdalemuir/support=
 You=20
will get lower noise if you make the top nearly flush with the ground / put=20=
a=20
vertical bar fence around the site. Maybe wood + wire paling? You may need t=
o=20
consider possible problems with high rainfall and flooding.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>What is=20
  the easiest way to run a long cable?  I do have massive bedrock 
o=
n=20
  the property about 300 ft from the house.


    A 300 ft cable run will very likely require you=
 to=20
provide lightning protection, but this depends on the location. A lot of the=
 US=20
has poor ground conduction and / or a deep water table. Check on t=
he=20
local advice? You can buy power cable with spiral steel wire reinforcing and=
=20
extra insulation so that it can be laid directly in a trench. This protects=20=
it=20
from ground movements, but it won't be cheap.  Otherwise you can=20
lay ordinary cable in polythene water=20
pipe.      
    The difficulty is in threading the cable throug=
h=20
the pipe. It has a very high total friction. If you have a=20
suitable quarry, cliff, bridge, stairwell, or tower, you can hang the pipe=20
vertically and feed the cable in from the top. Otherwise you need a smooth i=
ron=20
rod and a strong magnet. You use this to pull a cotton or similar strong str=
ing=20
through the pipe, then a strong cord and then the cable. You can put talc po=
wder=20
in the pipe to lubricate it. Suck the powder through first with a vacuum=20
cleaner? You can also use Molybdenum Disulphide or Graphite powder, but they=
 are=20
both messy.
 
    Hope that this helps,
 
    Chris Chapman