Hi All,  Chris your rain gutter idea is very interesting too.  Is there a 
pict illustrating the version of the Cascades used?

Here is a different question...   Picture a perfectly balanced beam, on a 
center pivot, just like a see-saw, with two kids of similar mass.
Would this beam tend to remain fixed during an earthquake?    I can 
visualize, how a diving board with a person on the end would respond, with 
the mass moving differently from the earth.   But I don't know if the 
see-saw, would tend to remain fixed/level as the earth isolated during an 
event.

cheers, Ted



--------------------------------------------------
From: 
Sent: Monday, June 10, 2013 9:51 AM
To: 
Subject: Re: Water/Laser geophone instrumentation

> From: Geoff 
> To: psnlist 
> Sent: Tue, 4 Jun 2013 20:13
> Subject: Water/Laser geophone instrumentation
>
>
> Hello PSN,
>
> TWO ideas to play with,
> I was just playing around with a drink container of water. The
> container was about 1/3 full. I took a laser pointer and reflected
> the laser light off the surface of the water. The reflection seemed
> to exhibit motion related to the water from which it was reflected.
> NOW,
> Would it be possible, to use a setup like this, to detect seismic
> motions ?
> 1. Tub of water of some design.
> 2. reflected laser light off the surface somehow.
> 3. laser light sensor to detect disturbances
>    down to the nano-meter of motion ??
> 4. at this moment in time, ignore planes of motion.
>
> Hi Geoff,
>
> ****I tried something similar using about 12 ft of rainwater gutter
> flat on the ground with sealed ends, part filled with water. There
> is a huge system like this in the Cascades. You use a calculated
> length to 'slop' oscillate from end to end at a given period, but
> you make the water depth shallow enough to give critical
> damping. I shone a red semiconductor laser off the centre of the
> trough at grazing incidence and looked at the fairly strong
> reflection about 40 ft away on a white wall. I had intended to make
> a long plastic float and attach a surface silvered mirror to the centre,
> to stop ripples due to air currents and to reduce evaporation, but
> the quality of the laser beam was so poor that the edges of the spot
> were all 'bobbly' and unusable. It might work better with a long
> He/Ne laser tube.
>
> In addition, how about an adaptive optics sensor like the
> astronomers use to detect tornadic or helical winds in the
> atmosphere ?
>
> ****What method do these use and what references do you have ?
>
>    Regards,
>
>     Chris Chapman
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