Karl,

Regarding your suggestion of visualizing the 6-second microseisms. 

It would take a very high Q (undamped) resonant system to get the 
1 to 5 micron motion up to some visible scheme, and even then some
optical magnification would be necessary..

But it would be fairly easy to amplify the output of a long period 
seismometer and connect the signal to a galvanometer or another 
seismometer. A light beam (pencil lasar (with a diffuser for safety)) 
shining off a mirror on the boom of the driven seismometer
to a screen on a wall would make the amplified ground motion quite
visible. The amplification can be adjusted for the best effect.
This would provide a dynamic demonstration of the "restless earth"
that people can relate to easier than minute wiggles on a PC screen.
And during a quake, the lasar spot would swing from the ceiling to
the floor.

There was a use of high Q physical resonance in the days of moving-
coil seismometers with galvanometric photo-recording. Since the whole
system was passive, filters were a problem. So to filter the 6-second
noise, a 6-second galvanometer was connected into the coupling network
so that it was half damped. It would oscillate with the 6-second noise
and absorb the energy.

Later when very large computer capacitors came along, I was able to 
make a twin-tee 6-second notch filter with an 80 ohm impedance (for the
galvo) that used 120 000 ufarad capacitors.

Regards,
Sean-Thomas

_____________________________________________________________________

Public Seismic Network Mailing List (PSN-L)