World's Largest Wheatstone Bridge

String a wire back and forth across / along a fault line to measure very small displacements in the earth's surface. If the resistance
and/or tensile strength needs to be higher than a common single alloy wire then structural steel cable could be wrapped around a insulated wire with a higher resistivity. It could be temperature compensated as usual, with another wire of the same length loosely supported nearby in another leg of the bridge.
An abandoned power line may be good to go if it is properly located.
Good info sometimes comes in small displacements.
Bret Cahill
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Typical Cahill comic book nonsense.
--
Jim Pennino

Remove .spam.sux to reply.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bret Cahill wrote:

Two gps stations on both sides do the same trick
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

What's the smallest displacement -- not movement but actual change in _distance_ between two points -- they can measure?
Bret Cahill
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bret Cahill wrote:

They measure continental drift with them in cm's per year....
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The warning might be in microns.
Bret Cahill
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 3 May 2010 19:39:58 -0700 (PDT), Bret Cahill

What warning? Faults creep all the time. Knowing the rate of creep has zero useful predictive value.
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

At constant speed?
If that were true all the acceleration measurements published by USGS or Cal Tech on the web in real time would always be zero.
There may be some characteristic behaviour of certain faults that could be highly reliable early warning info.

Has this been proven over long distances measuring displacements of a few thousandths of an inch?
Bret Cahill
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 3 May 2010 20:01:47 -0700 (PDT), Bret Cahill

Nobody is making useful earthquake predictions. It's probably impossible. A superficial surface measurement is obviously insufficient to understand an immensely complex and chaotic subsurface 3D system.
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That's the problem.

That may very well be somewhat true.

Maybe. Probably.
But why leave any stone unturned when _my_ safety is at stake?
Bret Cahill
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 3 May 2010 21:02:48 -0700 (PDT), Bret Cahill

Good point. Move to Mississippi and live in a tent and you will be in somewhat less terror of earthquakes.
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

At least they can predict hurricanes and oil slick movements. Anyone want to buy a used shrimper?
Why is earthquake insurance was so expensive? Unlike floods or fire it's pretty hard to fake an earthquake to defraud the insurance company.
Bret Cahill
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bret Cahill wrote, On 5/4/2010 11:25 AM:

Bret, Take a wooden pencil and very slowly bend it. You will begin to hear small cracking noises (mini earthquakes) as the wood fibers begin to fail. Then suddenly snap - the pencil will break (major earthquake)!
Now, run the experiment again. This time try to predict the exact millisecond that the pencil will break. Run the experiment a dozen times and see how you do. Its not easily. Every pencil is different. Even accurately knowing the load and the displacement on the pencil will not allow you to predict exactly when the pencil will snap. This experiment is very similar to predicting when an earthquake will occur.
Also, geologists already use strain meters (sometimes called borehole extensometers) to measure displacements across fault lines. See: <http://www.springerlink.com/content/x0833xv4j4qq02qj/ <http://www.visionsmart.com/turtlemountain/extensometer.htm <http://www.mhest.com/spotlight/earthquakes/articles/Seismographic_Instrumentation.pdf
--

Paul D Oosterhout
I work for SAIC (but I don't speak for SAIC)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bret Cahill wrote:

I would like to add a couple things:
1: How do you propose to discern signal of "a few thousandths of an inch" from noise including whatever harmless-and-usual deviations of-noise-type from cm-per-year scale plate movement?
I would worry more about somewhere having fault movement of a few millimeters within a day transferring stress to "where a big one will come from". If that does not cause a major earthquake within a day, then the "big quake" has fair chance of coming 20-30-plus years later.
I would also worry about "a big one" having mere few minutes of advance warning from significant acceleration of detection of "fault slips", along with likely a majority of these being "minor burps" as opposed to "the brown stuff hitting the fan".
Not that I want to discourage research in this area...
--
- Don Klipstein ( snipped-for-privacy@misty.com)

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It's just additional data. No one suggested there is any guarantee it will be any more worthwhile than Al Gore in a dust devil.
Motion detectors are good down to a few microns and millihertz but the really low frequency events are lost.

The state of the art is allowing a lot of people to get killed. With a couple hours warning you could even save a lot of personal effects if not buildings and infrastructure.
Bret Cahill
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

A seismometer is a really low frequency motion detector.
--
Jim Pennino

Remove .spam.sux to reply.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
news:1e80670c-07b7-4c3b-8578-

Which you plan to measure with string? What advantage does string offer over existing GPS and laser based devices?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 3 May 2010 09:46:39 -0700 (PDT), Bret Cahill

You cannot get a good enought temperature (and other factors) compensation with such a setup. A bird sitting on the wire would trigger a massive earthquake alarm, and the evacuation of San Francisco and Los Angeles and every clay hut in between, for example.
Sorry Bret, to disappoint you.
w.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Compensation for temp. and other factors is easy: Just loosely wrap another identical wire around the taught wire and shield and insulate it for another leg of the bridge.

They may have to use fake owls or bury it underground.

The data wouldn't be made available to the general public until after it was studied and determined to be useful in predicting earthquakes.
Supposing 95% of a certain kind of fault line gives some kind of micro displacement warning an hour or so in advance of an M 8.0?
Wouldn't that be worth an investigation?
The World's Largest Strain Gage might turn out to be pretty cost effective at saving lives and property.
Bret Cahill
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Wind.
Yet more silly, comic book engineering to solve a problem solved a long time ago.
The challenge to monitoring such stuff isn't an engineering problem, it is an economic problem.
--
Jim Pennino

Remove .spam.sux to reply.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.