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Subject: Re: Strain meters?
From: Karl Cunningham karlc@.......
Date: Sun, 21 May 2000 00:14:09 -0700

Jim --

I'm not sure what the magnitude of the expected strain is or how protected
the area is from vandalism, but here's some suggestions:

A frequently-used and very inexpensive method to measure horizontal strain
across a fault is to drive stakes at A and B (one on each side of the
fault, perhaps a meter on each side) and perhaps 5 meters apart along the

         stake-A                           C-stake
         stake-D                           B-stake

Anchor a wire to one of the stakes and stretch it along to the other one,
where it is attached by an extension spring.  Measuring the length of the
spring with a caliper, and compensating for change in the length of the
wire due to thermal expansion, gives a measure of strain along the fault.

A variation is to drive four stakes and to measure A-B, A-D, C-B, and D-C.
This gives a vector of movement and also gives redundant measurements for

For more cost, a quartz fiber instead of the wire will improve temperature
stability, and use of an LVDT instead of the calipers will improve
measurement resolution and stability.

And you can build a shelter over the apparatus to improve things even more.

Karl Cunningham

At 12:44 5/20/2000 -0700, you wrote:
>Sean Thomas et al,..
>A student at UNLV would like to measure movement across some fissures in
>Las Vegas.  The fissures are cracks in the soil (deep alluvium) about 10m
>long in an area of mapped faulting.  I was wondering if strain meters
>would do the trick, the cheaper the better,and can you recommend or
>suggest any methods or devices that would work?


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Larry Cochrane <cochrane@..............>