Ted,

One more thought.  Your observations triggered an idea that might prove 
useful for reducing the local noise sensitivity of a vertical pendulum 
sensor, i.e. one having a horizontal hinge axis.

If you construct a Nearly Balanced sensor or similar device which is mainly 
sensitive to tilt or rotation, and then if you used identical transducers 
on it and on the regular pendulum so that the sensitivity per degree of 
tilt was identical, and finally oriented them in the same direction, you 
could subtract the data from the nearly-balanced one from the regular 
pendulum to leave the seismic translation data, but remove the tilt noise, 
which I think may be mostly of higher frequency, and local in origin.

That might considerably reduce the noise level of the pendulum seismic 
data.  Of course that also eliminates the super low frequency tilt motions, 
like earth tides, etc. if that's what you were wanting to see.

BTW, in my previous post, at the beginning I think I interchanged E/W and 
N/S.  Hope that didn't confuse things too badly.

Regards,
Brett


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