> > This is what Sean-Thomas wrote about using a 4.5Hz geophone as a
broadband
> > sensor:
......
> >
> > But the data is too noisy for a sensitive broadband sensor, and I am
usually
> > barely able to see the normal 6-second microseism background of 1 to 2
> > microns/second. Of course these were very clear (~10x) when hurricane
> > Bonnie passed last August. I also made a nice record  (from St. Louis)
> > of the Ohio quake in September, with peak velocities of Lg of about 10
> > microns/second at about 8 seconds.

I can generally see the microseism background on my 4.5 Hz geophone systems.

For instance, here is some background noise data from today at ~17 UTC from
a shielded geophone system
http://www.infiltec.com/seismo/QM45-CL.jpg (geophone system)
sitting on the carpet of my basement office slab:

http://www.infiltec.com/seismo/061204N1.gif   (noise spectra)

The steep drop off above 4 Hz is due to the cutoff of an 8 pole Bessel
filter switched capacitor chip.  There is no digital filtering. The
microseism peak is ~ 0.24 Hz.

Here is a another example, a geophone detection of 2005 December 05 12:19
UTC
Magnitude 6.8 - LAKE TANGANYIKA REGION: 11,954.0 km from Bailey's
Crossroads, VA

http://www.infiltec.com/seismo/051205BS.jpg  (noise and quake)

that shows a teleseismic peak at ~0.05 Hz as well as a microseism peak at
~0.2 Hz.

Dave
http://www.infiltec.com/seismo/inf-qm45.htm

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