## PSN-L Email List Message

Subject: Re: Water/Laser geophone instrumentation
From: chrisatupw@.......
Date: Tue, 11 Jun 2013 20:38:12 -0400 (EDT)

```From: Ted Channel
To: psnlist
Sent: Tue, 11 Jun 2013 16:24
Subject: Re: Water/Laser geophone instrumentation

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

Hi Ted,

****Check out :-
http://www.geodesy.cwu.edu/instruments/tilt/

Here is a different question...   Picture a perfectly balanced beam, on
a centre pivot, just like a see-saw, with two kids of similar mass.
Would this beam tend to remain fixed during an earthquake?  But I don't
know if the see-saw, would tend to remain fixed/level as the earth
isolated during an event.

****A see saw may be stable if the hinge at the centre is slightly=20
raised
above the level of the line joining the centres of mass at both ends,
giving a pendulum with a large rotational moment of inertia and quite a
long period. This would not react to vertical motion, but it would
react a bit to horizontal motions parallel to the beam.
If the hinge lies on the line joining the centres of mass at both
ends, the see saw should not be effected by horizontal motions either,=20
or
by rotational ones.

Regards,

Chris

--------------------------------------------------
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.
>
> 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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