PSN-L Email List Message

Subject: Re: Shaking house
From: Bob Hancock icarus@.........
Date: Mon, 16 Feb 2009 17:44:07 -0700

Robert -

I have a seismometer located over 250 feet from my house.   However  
there are some things you might want to consider:

1.    How often will you be accessing the instrument - this will  
determine the type of vault and seismic pier that you set up (think  
depth and accessibility).  For example does you instrument require  
periodic tweaking, if so, how often will you need to have direct  
access to the instrument?

2.   What are your temperature extremes.  Do you live in an  
excessively wet or dry climate, snow or hot sun?  If you have an  
external seismic vault, is it weather protected, and how hard is it to  
access the instrument?

2.	Regardless of where you place the instrument, temperature  
stabilization is extremely important.  If you have the instrument  
temperature stabilized, you most likely have it covered, and this begs  
the question, how easy will it be to access the instrument for tweaking?

3.    Does your electronics require a differential receiver at the  
point where your signal enters your house?  This is in addition to and  
prior to the A/D board.  You might want to check if you need something  
like that.

4.    If you use a crawl space under a house, you will most likely  
pick up tilting ground movement as the house is buffeted by wind, and  
when people move around the house.  However, this is dependent upon  
the depth of the foundation, firmness of the ground, and external  
forces that affect the house.

5.   When I had my instrument located 75 feet from the house, I could  
pick up the washing machine.  I was able to filter it out when it  
coincided with a seismic event, but that is something to think about.

6.    The previous comment about the cable is very important.  Ultra- 
violet radiation can cut the life of an above ground cable.  You  
definitely want it buried, and placed inside something like PVC piping.

7.    If you use some variation of a wireless transmission between the  
instrument and your receiver, you need to think about the weather and  
wind again.  Do you have blowing dust and dirt where you live.  If you  
have periods of heavy rain, blowing dust or snow, it is likely that  
you could loose your signal at least during these occurrences.  You do  
not want that to happen during a seismic event.  You could get around  
that with some type of temporary data storage at the instrument site,  
and if the transmission cannot take place, it could be stored  
temporarily at the instrument, but like everything else this adds  
complexity and cost.

No simple answers - lots to think about.  There are many more factors  
to consider, but this will get you started in thinking about some of  
the benefits and problems associated with an external installation.

Bob Hancock


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