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.

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 -----
>>  
>> From:  Gary  Lindgren 
>>  
>> To: psn-l@..............
>>  
>> Sent: Thursday, August 28, 2008 9:59  AM
>>  
>> 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.
>>  
>>  
>> 
>> Please any thoughts  on preparing this space?
>>  
>>  
>> 
>>  
>>  
>>  
>> 
>> Thanks,  Ted
> 







Hi Te=
d -



When we lived in NJ, I operated a 3 channel MET seismometer in the crawl sp=
ace under my apartment.   I had the instrument sitting on a hexago=
nal cement block of 12 inches across and 2 inches thick, all covered with a =
Styrofoam bucket.  The building design included foundation walls that w=
ere 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, yo=
u may find that walking around your house will cause deflections of the inst=
ruments.  I have heard similar comments from individuals who have place=
d 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 adequat=
e.  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 cyc=
le.  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 fee=
t 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.  



Depending upon your yard size, you might consider a subsurface vault in a q=
uiet 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 co=
me as it settles.  I have found that after 1 1/2 years, I still get occ=
asional ground noise from settling dirt.



Another thought to consider is insulating your instrument from wind current=
s.  Seismometers are extremely sensitive to any wind flow and temperatu=
re 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 ins=
trument and covers it down to its base.  I have found this to be very e=
ffective and the bucket protects the instrument from both wind flow and ther=
mal variations.  Even in a sealed seismic vault you need to protect aga=
inst errant wind currents caused by uneven thermal heating of the vault as t=
he sun moves across the sky.



The key for a quiet instrument is reduction of cultural noise and wind nois=
e.  Things to consider is under a house you will most likely pick up mo=
vement 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 consid=
eration as the root structure causes ground tilt for a considerable distance=
..  Railroad tracks can transmit vibrations for miles.  The worst r=
ail noise comes from diamonds where one set tracks crosses another set of tr=
acks.  Major roads that are in poor repair with potholes and lots of se=
mi-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 ----- 

 

From:  Gary  Lindgren <mailto:gel@.................>  

 

To: psn-l@.............. 

 

Sent: Thursday, August 28, 2008 9:59  AM

 

Subject: craw space under house



Hi All,   &n=
bsp;I am building a new house.   This house has no basement, but h=
as a  24"? crawlspace under the house.   I have lots of =
time, to create a  space for my three sensors, under the house.  &=
nbsp;I could also place  them in the garage on the concrete floor. &nbs=
p; My thought was to enter  the crawlspace, and dig a small pit la=
rge enough to allow for elbow room, then  line the pit with concrete bl=
ocks to keep dirt away.  Perhaps  covering the floor area similarl=
y.  Concrete may not be the best  material.   I could al=
so pour a pad or small footing using  cement.

 

 



Please any thoughts &n=
bsp;on preparing this space?

 

 



 

 

 



Thanks,  Ted