PSN-L Email List Message

Subject: Questions
From: Roger Sparks rsparks@..........
Date: Wed, 18 Oct 2006 08:30:43 -0700

Hi Ted,

Congratulations on making your new seismometer operational.   Welcome to 
the hobby.

psn-l-digest-request@.............. wrote:
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> Subject: Questions
> From:    "tchannel" 
> Date:    Tue, 17 Oct 2006 12:30:51 -0600
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> I have finished my sensor, and have had it running for three days.
> 1.  During the night hours, 11pm to 6am, the tract goes from normal to =
> noisy, getting worse each hour.  The sensor sits in the garage on a =
> concrete slab.  No draft and no heat.  As soon as I go into the garage =
> in the AM and the room gets warmer, because the sun warms the room to =
> about 60 f. The trace returns to normal.  Is this temperature effect?  I =
> also turn off the monitor and turn it back on in the AM.  Could the CTR =
> or the computer create noise? They set about three feet from the sensor. =
> Again no heat, no draft and nothing running out there in the night.
You do not mention a cover over the seismometer.   A garage provides a 
cover which is much too large to prevent internal heat driven air 
currents which a seismometer will easily detect.   Try a much smaller 
cover over the seismometer.  The Plexiglas cover you are considering 
should be adequate, but you may also need some heating as suggested by 
Chris.   The heating should be less to control air currents, but would 
work more to stabilize heat related dimensional changes to the 
seismometer components.
> 2.   I think I am getting a good recording, I have see the last two =
> quakes and to me they look normal.
> I am in Boise Idaho and have tried to compare my .PSN with any others =
> close by.  However our local one in Boise is down and the next, nearest =
> one is in Washington State.   Now here is a hard question to ask:  I =
> created my expanded trace, using the same time plotted on the .PSN in =
> Washington (061017.013725.ebgz.psn M6.5 10356km from Ellensburg, Wa.,) =
> This was around one hour of trace.  I did this so I could compare the =
> two side by side.  I was a little surprised to see the Wa. psn to show a =
> large spike on the P and a short spike on the S.  My trace looks very =
> similar, but I show a large spike on the S and a smaller spike on the P. =
>   From the description of the Ellensburg Wa file it has a Z in it, is =
> that a Vertical sensor? and since my sensor is a Horz pointing N/S, =
> would that explain the different. These events came from the East, and I =
> have my beam pointing North.
> Anyone who would like me to send both .PSN's to them for a critique, =
> please email me.   I would appreciate someone looking at them and =
> voicing an opinion as to my level of gain, not sure if it is correct, =
> and some advise as to how to best filter this event to enhance the P and =
> S. I am just using trial and error.
Please post your files to the PSN web site.  The seismometer at ebgz is 
mostly vertical but has a tilt of about 20 degrees above horizontal and 
runs north/south. 

The best filter to use depends upon the quake so trial and error is the 
rule.  You will see quakes originating in Idaho or Montana much better 
if you use a high pass filter, passing frequencies of about 0.5 Hz and 
higher.   These local quakes will have frequencies present up to  about 
10 Hz.   Station ebgz 
demonstrates the effectiveness of a high pass filter on local quake data.
> 3.  Presently I am building a Plexiglas box.  But would it help to =
> reduce noise if I built a second box wrapped with alum foil?   Or other =
> ideas on building a box which would make a positive different?
> 4.   I know weather can alter the way the trace looks, I thought my =
> situation was weather, but it was clear today.
> What is there in a front moving thru that creates the noise?   Lets say =
> a front with little wind and no lightening.
> Many thanks, Ted
Best wishes,


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