In a message dated 12/08/2005, dwieck@............ writes:

I am in  the process of setting up a station. I have a set of Larry's 
geophones
and  his amplifier / filter boards along with his A/D board. I am trying to  
decide
the best place to place my sensors. I live in northwest TN  almost on top of 
the
New Madrid Fault. I want to set the geophones up  first then I may experiment
with some other sensors ( I am also collecting  parts to build a S-G sensor 
). I
have a couple of choices from the  reading I have done. I have several 
questions
about trying to decide  which would be the "best"  place to mount them. 

I have seen  references to mounting them in the crawl space of houses. This  
would
probably be one of the easier options. I can get under he  house easily and 
would
have short cable runs. I am not sure how  much of the house noise would be 
picked
up in this type location. It  is just a dirt base under the house right now..
Hi Dennis,
 
    Is it a timber house or one with brick/stone  walls? How many stories?
 
    Are they the 4.5 Hz geophones?
 
    So long as you stay away from the foundations, you  should not get too 
much house noise. I suggest that you try putting the  geophone under the house 
with the three legs pushed firmly into the soil and see  what results you get. 
Look for significant changes in the background  noise between no wind and 
strong wind conditions and keep some recordings  for reference. Also look out for 
spikes and interference signals, traffic or  other noise over 24 hrs. I 
connected my geophones up to the amplifier in a  portable radio and listened with 
headphones. OK, these signals aren't  the seismic ones, but you can often 
recognise noise sources by ear easier than  trying to figure them out from the 
traces. I start to hear  fast cars on the main road at about 1 km. There is a 
slightly depressed water  drain on the main road about 100 yards away which gives 
thump signals  occasionally with passing lorries..... Check for slamming doors 
and  windows, fridge start/stop, cooking loads, central heating timing, wind  
noise..... 
 
    If the under house installation is OK, you can  scoop out several inches 
of the topsoil and lay a 3 ft square concrete base in a  wood frame. You need 
to cover it with polythene to keep it 'wet' for maybe a  month to 'cure' 
fully. You use a 50:50 cement and sand mixture, no  gravel. Professional 
installations use a vibrator to remove air bubbles  from the wet mix after it is poured. 
You can get a lot out with a stick. Cement  can be quite corrosive in contact 
with metal, but you can use special paints.  You will have to leave adequate 
space for the thermal / draft screening box  if you are definitely going to 
use a SG horizontal; maybe a longer slab?

The second option would to build a small vault probably dug  in the ground  3 
or
4 feet deep. ( Most likely I would not be  able to get to bedrock). I have 
seen
several of this type on the web. I  live pretty much in the country on about 5
acres. Most of the land is  pretty hilly with a lot of trees.   
    You would have to make it water proof / adequately  drained / dry inside. 
See various websites for ways of doing this. 
_http://www.guralp.net/services/stations/eskdalemuir/_ (http://www.guralp.net/services/stations/eskdalemuir/)  
is  a professional example in soil which saturates with water. See also 
_http://seismo.berkeley.edu/seismo/bdsn/instrumentation/guidelines.html_ 
(http://seismo.berkeley.edu/seismo/bdsn/instrumentation/guidelines.html) 

I have  seen references saying that you need to be relatively far from trees 
etc or  the wind moving them will affect the sensors. If I do this I would 
have  further to run the cables back to the house. Is it better to have  the 
longer run from the sensors to the  boards or to have the A/D  output have the 
longer runs?


Trees may give broad band noise, but this may be  more serious for the longer 
period instruments. Aim to keep your sensors at  a distance equal to the 
height of the trees, minimum. This is very roughly the  expected extent of the 
roots. Exposed houses will also experience wind  noise.
    You have the problem of long cable runs and  probably some lightning 
protection required for installations away from the  house. Some soils have such 
poor electrical conductivity / are so dry that the  effective 'electrical 
ground surface' is several feet below ground level. All  your house electrical 
wiring is effectively sticking out above the  electrical ground! If lightning is a 
severe local hazard, you can use  intermittently charged batteries and a 
length of fibre optic cable to isolate  the digital signals. There are several 
websites with advice on this for various  states. You can bury cables in plastic 
water pipe. Pipe end fittings designed  for water tanks are readily available.
 
    Regards,
 
    Chris Chapman





In a message dated 12/08/2005, dwieck@............ writes:
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>I am in=20
  the process of setting up a station. I have a set of Larry's geophones
=
and=20
  his amplifier / filter boards along with his A/D board. I am trying to=20
  decide
the best place to place my sensors. I live in northwest TN=20
  almost on top of the
New Madrid Fault. I want to set the geophones =
;up=20
  first then I may experiment
with some other sensors ( I am also collect=
ing=20
  parts to build a S-G sensor ). I
have a couple of choices from the=20
  reading I have done. I have several questions
about trying to deci=
de=20
  which would be the "best"  place to mount them. 

I have seen=20
  references to mounting them in the crawl space of houses. This=20
  would
probably be one of the easier options. I can get under he=20
  house easily and would
have short cable runs. I am not sure h=
ow=20
  much of the house noise would be picked
up in this type location. =
It=20
  is just a dirt base under the house right now..
Hi Dennis,
 
    Is it a timber house or one with brick/stone=20
walls? How many stories?
 
    Are they the 4.5 Hz geophones?
 
    So long as you stay away from the foundations,=20=
you=20
should not get too much house noise. I suggest that you try putting the=
=20
geophone under the house with the three legs pushed firmly into the soil and=
 see=20
what results you get. Look for significant changes in the background=20
noise between no wind and strong wind conditions and keep some recordin=
gs=20
for reference. Also look out for spikes and interference signals, traffic or=
=20
other noise over 24 hrs. I connected my geophones up to the amplifier i=
n a=20
portable radio and listened with headphones. OK, these signals are=
n't=20
the seismic ones, but you can often recognise noise sources by ear easier th=
an=20
trying to figure them out from the traces. I start to he=
ar=20
fast cars on the main road at about 1 km. There is a slightly depressed wate=
r=20
drain on the main road about 100 yards away which gives thump signals=20
occasionally with passing lorries..... Check for slamming doors and=20
windows, fridge start/stop, cooking loads, central heating timing, wind=20
noise..... 
 
    If the under house installation is OK, you can=20
scoop out several inches of the topsoil and lay a 3 ft square concrete base=20=
in a=20
wood frame. You need to cover it with polythene to keep it 'wet' for maybe a=
=20
month to 'cure' fully. You use a 50:50 cement and sand mixture, no=20
gravel. Professional installations use a vibrator to remove air bubbles=
=20
from the wet mix after it is poured. You can get a lot out with a stick. Cem=
ent=20
can be quite corrosive in contact with metal, but you can use special paints=
..=20
You will have to leave adequate space for the thermal / draft screening=
 box=20
if you are definitely going to use a SG horizontal; maybe a longer slab?
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20
  size=3D2> The second option would to build a small vault probably&nbs=
p;dug=20
  in the ground  3 or
4 feet deep. ( Most likely I would not be=
=20
  able to get to bedrock). I have seen
several of this type on the web. I=
=20
  live pretty much in the country on about 5
acres. Most of the land is=20
  pretty hilly with a lot of trees.   
    You would have to make it water proof / adequat=
ely=20
drained / dry inside. See various websites for ways of doing this. http://www.gur=
alp.net/services/stations/eskdalemuir/ is=20
a professional example in soil which saturates with water. See also http://seismo.berkeley.edu/seismo/bdsn/instrumentation/guidelines.html
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>I have=20
  seen references saying that you need to be relatively far from trees etc o=
r=20
  the wind moving them will affect the sensors. If I do this I would ha=
ve=20
  further to run the cables back to the house. Is it better to have=20
  the longer run from the sensors to the  boards or to have the A/=
D=20
  output have the longer runs?


    Trees may give broad band noise, but this may b=
e=20
more serious for the longer period instruments. Aim to keep your sensor=
s at=20
a distance equal to the height of the trees, minimum. This is very roughly t=
he=20
expected extent of the roots. Exposed houses will also experience wind=20
noise.
    You have the problem of long cable runs an=
d=20
probably some lightning protection required for installations away from=
 the=20
house. Some soils have such poor electrical conductivity / are so dry that t=
he=20
effective 'electrical ground surface' is several feet below ground level. Al=
l=20
your house electrical wiring is effectively sticking out above the=20
electrical ground! If lightning is a severe local hazard, you can use=20
intermittently charged batteries and a length of fibre optic cable to isolat=
e=20
the digital signals. There are several websites with advice on this for vari=
ous=20
states. You can bury cables in plastic water pipe. Pipe end fittings designe=
d=20
for water tanks are readily available.
 
    Regards,
 
    Chris Chapman