World's Largest Wheatstone Bridge

[Bret Cahill]

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
Two gps stations on both sides do the same trick

What's the smallest displacement -- not movement but actual change in
_distance_ between two points -- they can measure?

Bret Cahill

They measure continental drift with them in cm's per year....

The warning might be in microns.


Bret Cahill

 

[Bret Cahill]

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

What you are trying to make is a strain gauge. This scheme wont work because
the gauge has to be attached to the substrate along it's whole length not
just strung up like a power line. But attaching it to the earth in any
meaningful way over distance would be next to impossible.

Tie it down every few feet.

Yes, you can
compensate for the temperature coefficient of resistance but how do you
compensate for the change in length due to temperature, coefficient of
expansion, a very different animal.

If you know the coefficient of expansion then you can correct for it,
either mechanically or later in the calculations.

I can't see a strain gauge being a
solution for seismic motions.

Is there any other way to measure very low frequency / very small
displacements?

The best way is a laser interferometer for small displacements and GPS or
gross measurements. Only two points need to be attached to the earth with
these schemes.

What's the accuracy?


Bret Cahill

 

[Bret Cahill]

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

Differential GPS and laser rangefinders make a lot more sense.

Laser rangefinders can work over dozens to hundreds of miles in a dust
storm or rainstorm?

To the nearest few microns?


Bret Cahill

 

[Bret Cahill]

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
Two gps stations on both sides do the same trick

What's the smallest displacement -- not movement but actual change in
_distance_ between two points -- they can measure?

Bret Cahill

They measure continental drift with them in cm's per year....

The warning might be in microns.

Bret Cahill

What warning? Faults creep all the time.

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.

Knowing the rate of creep has
zero useful predictive value.

Has this been proven over long distances measuring displacements of a
few thousandths of an inch?


Bret Cahill

 

In sci.physics Bret Cahill <BretCahill@peoplepc.com> wrote:

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


The problem is just to the East of Laguna Salada:

http://maps.google.com/maps?f=q&hl=en&q=32.2006,-115.4625(M3.0+-+Baja+California,+Mexico+-+2010+May+04+02:35:27+UTC)&t=h&z=9&iwloc=A

String a thin steel wire from Aqua Matias to Cucapa returning with a
larger diameter copper wire with a resistance << than the steel.

All those << M 1.0 movements can now be documented and studied.


Bret Cahill

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.


--
Jim Pennino

Remove .spam.sux to reply.

 

In sci.physics Bret Cahill <BretCahill@peoplepc.com> wrote:

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

Differential GPS and laser rangefinders make a lot more sense.

Laser rangefinders can work over dozens to hundreds of miles in a dust
storm or rainstorm?

Hundreds of miles, nope, but when combined with GPS you don't need lasers
to go hundreds of miles.

To the nearest few microns?

Over hundreds of miles microns are meaningless and in the noise of numerous
factors.


--
Jim Pennino

Remove .spam.sux to reply.

 

[Bret Cahill]

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
Two gps stations on both sides do the same trick

What's the smallest displacement -- not movement but actual change in
_distance_ between two points -- they can measure?

Bret Cahill

They measure continental drift with them in cm's per year....

The warning might be in microns.

Bret Cahill

What warning? Faults creep all the time.

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.

Knowing the rate of creep has
zero useful predictive value.

Has this been proven over long distances measuring displacements of a
few thousandths of an inch?

Bret Cahill

Nobody is making useful earthquake predictions.

That's the problem.

It's probably
impossible.

That may very well be somewhat true.

A superficial surface measurement is obviously
insufficient to understand an immensely complex and chaotic subsurface
3D system.

Maybe. Probably.

But why leave any stone unturned when _my_ safety is at stake?


Bret Cahill

 

[Bret Cahill]

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

The problem is just to the East of Laguna Salada:

http://maps.google.com/maps?f=q&hl=en&q=32.2006,-115.4625(M3.0+-+Baja+California,+Mexico+-+2010+May+04+02:35:27+UTC)&t=h&z=9&iwloc=A

String a thin steel wire from Aqua Matias to Cucapa returning with a
larger diameter copper wire with a resistance << than the steel.

All those << M 1.0 movements can now be documented and studied.


Bret Cahill

 

[Don Klipstein]

In <671d96b8-9355-48b0-afdb-1174e7683791@a27g2000prj.googlegroups.com>,
Bret Cahill wrote:

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
Two gps stations on both sides do the same trick

What's the smallest displacement -- not movement but actual change in
_distance_ between two points -- they can measure?

Bret Cahill

They measure continental drift with them in cm's per year....

The warning might be in microns.

Bret Cahill

What warning? Faults creep all the time.

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.

Knowing the rate of creep has zero useful predictive value.

Has this been proven over long distances measuring displacements of a
few thousandths of an inch?

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 (don@misty.com)

 

[Cwatters]

"Bret Cahill" <BretCahill@peoplepc.com> wrote in message
news:1e80670c-07b7-4c3b-8578-

The warning might be in microns.
Bret Cahill

Which you plan to measure with string? What advantage does string offer over
existing GPS and laser based devices?

 

[Cwatters]

"Bret Cahill" <BretCahill@peoplepc.com> wrote in message
news:120c41b8-59e1-438b-91f0-829eeabeb471@a2g2000prd.googlegroups.com...

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

Differential GPS and laser rangefinders make a lot more sense.

Laser rangefinders can work over dozens to hundreds of miles in a dust
storm or rainstorm?

To the nearest few microns?

Bret Cahill

How does string work over hundreds of miles ins a dust storm?

 

[Androcles]

"Cwatters" <colin.wattersNOSPAM@TurnersOakNOSPAM.plus.com> wrote in message
news:cMydnfrSg9jXk33WnZ2dnUVZ8iOdnZ2d@brightview.co.uk...

"Bret Cahill" <BretCahill@peoplepc.com> wrote in message
news:120c41b8-59e1-438b-91f0-829eeabeb471@a2g2000prd.googlegroups.com...
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

Differential GPS and laser rangefinders make a lot more sense.

Laser rangefinders can work over dozens to hundreds of miles in a dust
storm or rainstorm?

To the nearest few microns?

Bret Cahill

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.

 

[Bob Masta]

On Mon, 3 May 2010 21:16:15 -0700 (PDT), Bret
Cahill <BretCahill@peoplepc.com> wrote:

String a wire back and forth across / along a fault line to measure
very small displacements in the earth's surface. =A0If 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. =A0It 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


The problem is just to the East of Laguna Salada:

http://maps.google.com/maps?f=3Dq&hl=3Den&q=3D32.2006,-115.4625(M3.0+-+Baja=
+California,+Mexico+-+2010+May+04+02:35:27+UTC)&t=3Dh&z=3D9&iwloc=3DA

String a thin steel wire from Aqua Matias to Cucapa returning with a
larger diameter copper wire with a resistance << than the steel.

All those << M 1.0 movements can now be documented and studied.

Not clear what's the point of the different
metals.

Do you mean "string" as in suspended in space?
Exercise for the student: Compute the stress on
the wire just due to gravity.

Now imagine you actually got this to (nominally)
work. How are you going to allow for the change
in load due to wind, rain, and dust? What happens
when birds perch on it?

As it turns out, they've been using laser
interferometry for just this purpose for decades.

Best regards,


Bob Masta

DAQARTA v5.10
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
DaqMusic - FREE MUSIC, Forever!
(Some assembly required)
Science (and fun!) with your sound card!

 

[John Larkin]

On Mon, 3 May 2010 21:02:48 -0700 (PDT), Bret Cahill
<BretCahill@peoplepc.com> wrote:

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
Two gps stations on both sides do the same trick

What's the smallest displacement -- not movement but actual change in
_distance_ between two points -- they can measure?

Bret Cahill

They measure continental drift with them in cm's per year....

The warning might be in microns.

Bret Cahill

What warning? Faults creep all the time.

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.

Knowing the rate of creep has
zero useful predictive value.

Has this been proven over long distances measuring displacements of a
few thousandths of an inch?

Bret Cahill

Nobody is making useful earthquake predictions.

That's the problem.

It's probably
impossible.

That may very well be somewhat true.

A superficial surface measurement is obviously
insufficient to understand an immensely complex and chaotic subsurface
3D system.

Maybe. Probably.

But why leave any stone unturned when _my_ safety is at stake?

Good point. Move to Mississippi and live in a tent and you will be in
somewhat less terror of earthquakes.

John

 

[Paul O]

Bret Cahill wrote, On 5/4/2010 11:25 AM:

snip
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,

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)

 

[Bret Cahill]

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
Two gps stations on both sides do the same trick

What's the smallest displacement -- not movement but actual change in
_distance_ between two points -- they can measure?

Bret Cahill

They measure continental drift with them in cm's per year....

The warning might be in microns.

Bret Cahill

What warning? Faults creep all the time.

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.

Knowing the rate of creep has zero useful predictive value.

Has this been proven over long distances measuring displacements of a
few thousandths of an inch?

  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?

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.

  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...

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

 

In sci.physics Bret Cahill <BretCahill@peoplepc.com> wrote:

Motion detectors are good down to a few microns and millihertz but the
really low frequency events are lost.

A seismometer is a really low frequency motion detector.


--
Jim Pennino

Remove .spam.sux to reply.

 

[Bob Eld]

"Bret Cahill" <BretCahill@peoplepc.com> wrote in message
news:cbd8dbe2-93eb-4ed1-ac8c-08b4e000ac69@11g2000prw.googlegroups.com...

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

What you are trying to make is a strain gauge. This scheme wont work
because
the gauge has to be attached to the substrate along it's whole length not
just strung up like a power line. But attaching it to the earth in any
meaningful way over distance would be next to impossible.

Tie it down every few feet.

Yes, you can
compensate for the temperature coefficient of resistance but how do you
compensate for the change in length due to temperature, coefficient of
expansion, a very different animal.

If you know the coefficient of expansion then you can correct for it,
either mechanically or later in the calculations.

I can't see a strain gauge being a
solution for seismic motions.

Is there any other way to measure very low frequency / very small
displacements?

The best way is a laser interferometer for small displacements and GPS or
gross measurements. Only two points need to be attached to the earth with
these schemes.

What's the accuracy?

Bret Cahill

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.

 

[Bret Cahill]

String a wire back and forth across / along a fault line to measure
very small displacements in the earth's surface. =A0If 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. =A0It 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

The problem is just to the East of Laguna Salada:

http://maps.google.com/maps?f=3Dq&hl=3Den&q=3D32.2006,-115.4625(M3..0+...
+California,+Mexico+-+2010+May+04+02:35:27+UTC)&t=3Dh&z=3D9&iwloc=3DA

String a thin steel wire from Aqua Matias to Cucapa returning with a
larger diameter copper wire with a resistance << than the steel.

All those << M 1.0 movements can now be documented and studied.

Not clear what's the point of the different
metals.

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.

Do you mean "string" as in suspended in space?
Exercise for the student:  Compute the stress on
the wire just due to gravity.

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.

Now imagine you actually got this to (nominally)
work.  How are you going to allow for the change
in load due to wind, rain, and dust?  What happens
when birds perch on it?

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.

As it turns out, they've been using laser
interferometry for just this purpose for decades.

The resolution needs to be one part per 100 billion.


Bret Cahill

 

[Bret Cahill]

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
Two gps stations on both sides do the same trick

What's the smallest displacement -- not movement but actual change in
_distance_ between two points -- they can measure?

Bret Cahill

They measure continental drift with them in cm's per year....

The warning might be in microns.

Bret Cahill

What warning? Faults creep all the time.

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.

Knowing the rate of creep has
zero useful predictive value.

Has this been proven over long distances measuring displacements of a
few thousandths of an inch?

Bret Cahill

Nobody is making useful earthquake predictions.

That's the problem.

 It's probably
impossible.

That may very well be somewhat true.

A superficial surface measurement is obviously
insufficient to understand an immensely complex and chaotic subsurface
3D system.

Maybe.  Probably.

But why leave any stone unturned when _my_ safety is at stake?

Good point. Move to Mississippi and live in a tent and you will be in
somewhat less terror of earthquakes.

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