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
Tie it down every few feet. =========================================== Do manual work in a dust storm or rainstorm? That was one of your objections to laser ranging, right? 'Faced with changing one's mind, or proving that there is no need to do so, most people get busy on the proof.'- John Kenneth Galbraith 'There is nothing so easy but that it becomes difficult when you do it with reluctance.'- Marcus Tullius Cicero
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
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
The problem is just to the East of Laguna Salada:
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...
Obviously you have no clue what "Wheatstone Bridge" means and are just, once again, throwing out technical terms you think will impress people with your knowledge.
Hundreds of miles, nope, but when combined with GPS you don't need lasers to go hundreds of miles.
Over hundreds of miles microns are meaningless and in the noise of numerous factors.
Which you plan to measure with string? What advantage does string offer over existing GPS and laser based devices?
How does string work over hundreds of miles ins a dust storm?
Apparently one nails it down every yard to get dust up one's nose.
Good point. Move to Mississippi and live in a tent and you will be in somewhat less terror of earthquakes.
John
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
The strain gage wire must have some resistance but it'll take a lot of low resistance wire to get all the terminals in one location.
No one wonders "where am I going to get 3" of wire with a low enough resistance" to wire up common thumb nail size strain gages.
Prestress isn't a problem with strain gages. Just stay in the elastic region. Moreover, in this application 4 sig figs might not be necessary.
Also decreasing the sag/length ratio of a catenary increases the sensitivity. A small displacement in the horizontal causes a large increase in tension and resistance.
They already get down to a few microns in the millihertz range with motion detectors. The goal here is longer warning times meaning small displacements at even lower frequencies or DC velocity. Higher frequency noise can be filtered.
If necessary the wires could be under or inside PVC.
The resolution needs to be one part per 100 billion.
Bret Cahill
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
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:
A seismometer is a really low frequency motion detector.
Tie it down every few feet.
If you know the coefficient of expansion then you can correct for it, either mechanically or later in the calculations.
Is there any other way to measure very low frequency / very small displacements?
What is the accuracy of a laser interferometer? Fractions of a wave length of light: nanometers. How accurate do you want it?
If you think you can make a strain gauge by hanging a some wire on poles space a few feet apart, then test your theory and set up such a scheme in your back yard. See if you can detect the vibration of nearby traffic or the earth tides every time the sun goes across the sky. I think you'll find it WONT WORK! But, prove me wrong. If you can show it works then great, more power to ya.
Mounting a conventional strain gage just at the ends would give you the same output assuming you had the dexterity to glue just the ends. dl/l should be const. over the entire area of the strain gage site.
Correcting for thermal expansion would require temperature data over the entire length.
Adding a +/- nanometer error to a +/- meter error just gives you a +/- meter error.
GPS wouldn't be useful for the actual data.
They claim laser interferometry won't work over long distances, i.e.,
50 km, but they are probably thinking of measuring an entire unknown distance when all that is really necessary is a _change_ in distance.Maybe use several different meters at different wavelengths so that you don't skip a wave.
Bret Cahill
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