Fascinating collection of information -- you've got the eye of a =
forensics
engineer. I'm going to do a bit of shooting from the hip here, so don't =
put
too much reliance on my guesses.

I agree that a particularly likely strong source is the radio tower =
behind
you. The guy wires are visible in the photo -- and they don't appear to =
have
any dampers on them (at least not within the view of the camera. One
particular event in your record (that you identified as the initial high
winds) at 7:28 suggests the tower (its components) had gone into a =
resonant
mode lasting about 2-minutes with a relatively constant amplitude. You =
can
eventually sort-out how much of a signal you get from the tower by =
keeping
(or getting) a log of wind speed and direction. Then compare that data =
to
associated recordings from the seismometer. There are undoubtedly a =
plethora
of common frequencies associated with the tower and its guy wires.

I do a fair amount of work in structural and ground-transmitted =
vibrations.
In virtually all of my long-term setups, I always have provisions to =
shut
the acquisition system down as thunderstorms approach the region. One of =
the
things I'd like to have is a database of characteristic ground responses =
to
thunder. Perhaps you have some of that information wrapped-up in your
records. You might check with the local weather service office to see if =
you
can get access to their lightning-strike database. I've got a sneaky
suspicion that some of the higher spikes may be the initial shock from a
lightning strike.

One of the things I sometimes find useful when analyzing long strings of
vibration data is to convert the record into an audio file. In this =
case,
we'd have to fool the file translator into thinking the sampling rate =
was
about 1kH or higher rather than your actual slow rate.

Obviously, a lot more information can be visually extracted if we =
weren't
faced with the inherent clutter of the drum-recorder format.

The exceptionally low-frequency responses at 6:52 and 7:37 appear to be
almost identical in magnitude and phase -- is that some artifact of your
system, I just cannot rationalize that they represent natural events.

I'd be very interested in looking at your digital files to see what =
usable
info can be extracted. Contact me off-line if you like.

Finally, what is the natural frequency of your system?

Regards,

-Tim-

Timothy Carpenter, P.E., Pres.,
GeoDynamics Consultants, Inc.
5043 Whitlow Ct.
Commerce Twp., Mi 48382
248-363-4529 (voice & fax)
248-766-1629 (cell)
geodynamics@........... (primary)
geodynamics@....... (secondary)
=A0


-----Original Message-----
From: psn-l-request@.............. [mailto:psn-l-request@............... =
On
Behalf Of Thomas Dick
Sent: Friday, December 02, 2005 3:14 PM
To: psn-l@..............
Subject: tornadoes and earthquake detection

Below is a section of my website where I have posted stuff on the Nov, 6 =
F3=20
tornado that passed by me. I am sure many of you don't have tornadoes=20
passing by your equipment very often. If you will click on November 6 F3 =

...... at this site http://home.insightbb.com/~dickthomas01/, you will =
see=20
some of the damage and data. Your comments and expertise would be=20
appreciated.=20


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