Geoff,

Using a fluid as a mass is very much along the lines of what Dave 
Nelson was working on for his miniature horizontal.  It doesn't work 
so well for vertical designs, since for those you need to support the 
liquid column with something which doesn't change even slightly with 
temperature or outside pressure.  So far he hadn't found anything 
that works well for that.

This has two helicorder traces and a picture, but Dave says that the 
N/S channel has a problem that he's going to be looking into.
http://bnordgren.org/seismo/gif_images2.htm

To see what's inside and see an analysis of its frequency response:
http://bnordgren.org/seismo/FMES2.zip

Dave's electronics extends the flat portion of its velocity response 
down to somewhat lower frequencies so that it sees teleseisms better.
It is quite sensitive.

Regards,
Brett

See:

At 04:59 PM 11/7/2010, you wrote:
>Possibly float a magnet on the surface
>held in place by whatever and then
>have a coil on the wall of the well ?
>
>or, vice versa.
>
>getting the stuff into place is a big wonder.
>
>I often thought a big water tower might make a good
>vertical sensor if you hydraulically amplify
>the pressure changes related to ground motion.
>The water is a fluid and non-compressible
>with lots of mass and momentum, every tiny undulation should
>cause considerable pressure change.
>
>Sort of like a little pressure on the break pedal causes
>big pressure in the hydraulic cylinders.
>
>When I look at the water tower at Falcon Field
>at Mesa AZ, I often think of it as a potential seismometer.
>
>But such a thing must be dedicated only to sensing.
>
>Maybe a denser fluid like mercury ?
>
>A barometer like device that reacts to motion
>instead of air pressure.
>
>geoff


__________________________________________________________

Public Seismic Network Mailing List (PSNLIST)

To leave this list email PSNLIST-REQUEST@.............. with 
the body of the message (first line only): unsubscribe
See http://www.seismicnet.com/maillist.html for more information.