Re: crawl space under houseHi Bob,  Thanks for =
sharing...........Presently my sensors are in the basement on a concrete =
floor.   Yes I do see people walking upstairs, but mostly if I place the =
sensor close to a vertical wall.
My new house set on a new foundation, so as you point out I may get a =
lot of noise as the house settles.   We shall see.   All your =
information is good to know.

Ted
  ----- Original Message -----=20
  From: Bob Hancock=20
  To: psn-l@.................
  Sent: Saturday, August 30, 2008 12:40 PM
  Subject: Re: crawl space under house


  Hi Ted -

  When we lived in NJ, I operated a 3 channel MET seismometer in the =
crawl space under my apartment.   I had the instrument sitting on a =
hexagonal cement block of 12 inches across and 2 inches thick, all =
covered with a Styrofoam bucket.  The building design included =
foundation walls that were placed several feet in the soil, including =
individual foundations walls between each apartment.  Although I had the =
instrument more or less in the middle of the area, I found that as I =
walked on the floor above, I could see that motion on the instrument.  =
Depending upon your foundation, you may find that walking around your =
house will cause deflections of the instruments.  I have heard similar =
comments from individuals who have placed instruments in basements or on =
garage floors.

  When we moved to Arizona, I tried a variety of locations including =
under my house, in a nearby storage shed and in my workshop.  None were =
adequate.  I finally placed the instrument in the ground, first about 75 =
feet away and I could always tell when the washing machine when into the =
spin cycle.  I finally moved the instrument about 250 feet from the =
house where I get a minimum of wind and cultural noise.  The road is =
about 400 feet from the instrument and I can see vehicles striking =
potholes in the road.  I find that if I drive my garden tractor within =
50 feet of my vault, I can see movement on the instrument. =20

  Depending upon your yard size, you might consider a subsurface vault =
in a quiet area, away from trees and any buildings.  It is very =
difficult to remove cultural noise as I have found.  However, you should =
be careful and do not disturb any more dirt than you need.  Dirt once =
disturbed is difficult to re-compact and will be a source of noise for a =
long time to come as it settles.  I have found that after 1 1/2 years, I =
still get occasional ground noise from settling dirt.

  Another thought to consider is insulating your instrument from wind =
currents.  Seismometers are extremely sensitive to any wind flow and =
temperature change.  In my setup, I first covered my instrument with =
sand bags, and that did a good job of insulating the instrument from =
thermal variation and wind flow.  However, they were hard to remove from =
the hole, and I settled on a large bucket lined with fiberglass which =
sits on top of the instrument and covers it down to its base.  I have =
found this to be very effective and the bucket protects the instrument =
from both wind flow and thermal variations.  Even in a sealed seismic =
vault you need to protect against errant wind currents caused by uneven =
thermal heating of the vault as the sun moves across the sky.

  The key for a quiet instrument is reduction of cultural noise and wind =
noise.  Things to consider is under a house you will most likely pick up =
movement of people in the house, and tilt from the house in times of =
high and possibly even moderate winds.  You proximity to trees is =
another consideration as the root structure causes ground tilt for a =
considerable distance.  Railroad tracks can transmit vibrations for =
miles.  The worst rail noise comes from diamonds where one set tracks =
crosses another set of tracks.  Major roads that are in poor repair with =
potholes and lots of semi-trailers are another source of cultural =
noise.......Just some thoughts to consider.

  Good luck on your location wherever you choose it.

  Bob Hancock




      ----- Original Message -----=20
      =20
      From:  Gary  Lindgren  =20
      =20
      To: psn-l@.................
      =20
      Sent: Thursday, August 28, 2008 9:59  AM
      =20
      Subject: craw space under house

      Hi All,    I am building a new house.   This house has no =
basement, but has a  24"? crawlspace under the house.   I have lots of =
time, to create a  space for my three sensors, under the house.   I =
could also place  them in the garage on the concrete floor.   My thought =
was to enter  the crawlspace, and dig a small pit large enough to allow =
for elbow room, then  line the pit with concrete blocks to keep dirt =
away.  Perhaps  covering the floor area similarly.  Concrete may not be =
the best  material.   I could also pour a pad or small footing using  =
cement.

      =20

      Please any thoughts  on preparing this space?

      =20

      =20
      =20
      =20

      Thanks,  Ted











Hi Bob,  Thanks for=20
sharing...........Presently my sensors are in the basement on a concrete =

floor.   Yes I do see people walking upstairs, but mostly if I =
place=20
the sensor close to a vertical wall.
My new house set on a new foundation, =
so as you=20
point out I may get a lot of noise as the house settles.   We =
shall=20
see.   All your information is good to know.
 
Ted

  
----- Original Message ----- 
  From:=20
  Bob=20
  Hancock 
  
To: psn-l@.............. 
  
Sent: Saturday, August 30, 2008 =
12:40=20
  PM
  
Subject: Re: crawl space under=20
house
  

Hi Ted -

When we lived in NJ, I =
operated a 3=20
  channel MET seismometer in the crawl space under my apartment. =
  I=20
  had the instrument sitting on a hexagonal cement block of 12 inches =
across and=20
  2 inches thick, all covered with a Styrofoam bucket.  The =
building design=20
  included foundation walls that were placed several feet in the soil, =
including=20
  individual foundations walls between each apartment.  Although I =
had the=20
  instrument more or less in the middle of the area, I found that as I =
walked on=20
  the floor above, I could see that motion on the instrument. =
 Depending=20
  upon your foundation, you may find that walking around your house will =
cause=20
  deflections of the instruments.  I have heard similar comments =
from=20
  individuals who have placed instruments in basements or on garage=20
  floors.

When we moved to Arizona, I tried a variety of =
locations=20
  including under my house, in a nearby storage shed and in my workshop. =

   None were adequate.  I finally placed the instrument in the =
ground,=20
  first about 75 feet away and I could always tell when the washing =
machine when=20
  into the spin cycle.  I finally moved the instrument about 250 =
feet from=20
  the house where I get a minimum of wind and cultural noise.  The =
road is=20
  about 400 feet from the instrument and I can see vehicles striking =
potholes in=20
  the road.  I find that if I drive my garden tractor within 50 =
feet of my=20
  vault, I can see movement on the instrument.  

Depending =
upon your=20
  yard size, you might consider a subsurface vault in a quiet area, away =
from=20
  trees and any buildings.  It is very difficult to remove cultural =
noise=20
  as I have found.  However, you should be careful and do not =
disturb any=20
  more dirt than you need.  Dirt once disturbed is difficult to =
re-compact=20
  and will be a source of noise for a long time to come as it settles. =
 I=20
  have found that after 1 1/2 years, I still get occasional ground noise =
from=20
  settling dirt.

Another thought to consider is insulating your=20
  instrument from wind currents.  Seismometers are extremely =
sensitive to=20
  any wind flow and temperature change.  In my setup, I first =
covered my=20
  instrument with sand bags, and that did a good job of insulating the=20
  instrument from thermal variation and wind flow.  However, they =
were hard=20
  to remove from the hole, and I settled on a large bucket lined with =
fiberglass=20
  which sits on top of the instrument and covers it down to its base. =
 I=20
  have found this to be very effective and the bucket protects the =
instrument=20
  from both wind flow and thermal variations.  Even in a sealed =
seismic=20
  vault you need to protect against errant wind currents caused by =
uneven=20
  thermal heating of the vault as the sun moves across the =
sky.

The key=20
  for a quiet instrument is reduction of cultural noise and wind noise.=20
   Things to consider is under a house you will most likely pick up =

  movement of people in the house, and tilt from the house in times of =
high and=20
  possibly even moderate winds.  You proximity to trees is another=20
  consideration as the root structure causes ground tilt for a =
considerable=20
  distance.  Railroad tracks can transmit vibrations for miles. =
 The=20
  worst rail noise comes from diamonds where one set tracks crosses =
another set=20
  of tracks.  Major roads that are in poor repair with potholes and =
lots of=20
  semi-trailers are another source of cultural noise.......Just some =
thoughts to=20
  consider.

Good luck on your location wherever you choose =
it.

Bob=20
  Hancock

  


    

----- Original Message -----=20
      
 
From:  Gary  Lindgren <mailto:gel@.................>=
;=20
       
 
To: psn-l@.................
      
 
Sent: Thursday, August 28, 2008 9:59=20
       AM
 
Subject: craw space under=20
      house

Hi All,=20
         I am building a new house.   This =
house has no=20
      basement, but has a  24"? crawlspace under the house. =
  I=20
      have lots of time, to create a  space for my three sensors, =
under the=20
      house.   I could also place  them in the garage on =
the=20
      concrete floor.   My thought was to enter  the =
crawlspace,=20
      and dig a small pit large enough to allow for elbow room, then =
 line=20
      the pit with concrete blocks to keep dirt away.  Perhaps=20
       covering the floor area similarly.  Concrete may not be =
the=20
      best  material.   I could also pour a pad or small =
footing=20
      using  cement.

 

Please any thoughts  on preparing =
this=20
      space?

 

 
 
 

Thanks,=20
       Ted