# Earths Axis has moved!

curiouschris
Reports being aired in the press about the earths axis having moved.

Well I think its a load of codswallop. but the press is reporting this as if its real. For such an event to occur would mean that all the stars would have moved in relation to the earth by a small amount, which means every astronomer would need to recalibrate their equipment.

I have not heard of this happening.

It seems the actual explanation is the earth's "figure axis" has moved. As I understand it this is an axis drawn through the earths center of gravity, and not the real axis. so in other words the earth has not moved but over time may re adjust to the new alignment should no other events cause another re alignment.

And what is a figure axis really?

CC

Homework Helper
Where did you hear this? The Earth's axis is indeed constantly and somewhat unpredictably fluctuating, an effect called nutation. A more long-term and predictable effect is precession, which astronomers do have to adjust for. On geological time scales, there's also true polar wander due to the movement of Earth's tectonic plates.

curiouschris
Sorry should have said it was in respect to the chile earthquake.

I am not talking about geological time scales I am talking about when the earthquake occured.

curiouschris
But did it really?

... shortened an Earth day by 1.26 millionths of a second ...

The Chilean quake was a so-called thrust earthquake, which occurs when a large section of the Earth's surface—in this case, the Nasca tectonic plate—dives beneath an adjacent plate. This process, called subduction, can cause earthquakes and volcanic eruptions

So one plate goes below another which means the net result should be approximately zero. eg: one plate falls the nearby plate rises to accommodate it.

Gross also estimates that the Chile earthquake shifted Earth's figure axis by about three inches (eight centimeters).

Deviating roughly 33 feet (10 meters) from the north-south axis around which Earth revolves, the figure axis is the imaginary line around which the world's unevenly distributed mass is balanced.

This is the disturbing part, most media stories skip the word 'figure' so they discuss the actual axis which is incorrect. from what I can determine the earth's center of gravity may have changed therefore its figure axis which in turn may cause actual movement of the real axis (that which the earth rotates about) over a period of time

but my conclusion above about the negating effect of the two plates should also apply.

CC

MotoH
Damn you mother nature!

This has happened before:
By speeding up Earth's rotation, the magnitude 8.8 earthquake—the fifth strongest ever recorded, according to the USGS—should have shortened an Earth day by 1.26 millionths of a second, according to new computer-model calculations by geophysicist Richard Gross of NASA's Jet Propulsion Laboratory in California.

For comparison, the same model estimated that the magnitude 9 Sumatra earthquake in December 2004 shortened the length of a day by 6.8 millionths of a second.

And I don't remember if there was a huge hubub about it, But we are still floating around generally well.

Nothing to see here.

Gold Member
But the Earth's rotation is also slowly slowing down due to tidal friction...anyone have an estimate on that rate, and how the change in rotation speed due to this earthquake is comparable?

BackEMF
But the Earth's rotation is also slowly slowing down due to tidal friction...anyone have an estimate on that rate, and how the change in rotation speed due to this earthquake is comparable?

Yes, the moon causes an increase in the length of the day by about 15 $\mu s$ each year by pulling on the earth. So this decrease of about 1 $\mu s$ will be quickly absorbed.

Any change in the distribution of mass of a rotating body has the potential to change its rotating speed i.e. you are changing the moment of intertia. Think of an ice skater pulling in their arms and thus spinning faster, similarly the change in the shape of the earth due to the Chilean earthquake (which must have reduced the oblateness of the earth slightly) has caused the earth to spin slightly faster, thus shortening the day.

See http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake under "Energy released by the earthquake"

physixlover
Where did you hear this? The Earth's axis is indeed constantly and somewhat unpredictably fluctuating, an effect called nutation. A more long-term and predictable effect is precession, which astronomers do have to adjust for. On geological time scales, there's also true polar wander due to the movement of Earth's tectonic plates.
on news-

http://uk.news.yahoo.com/5/20100303/twl-powerful-chile-quake-shifted-earth-s-3fd0ae9.html [Broken]

Last edited by a moderator:
twofish-quant
Simply, when we measure force of gravity ( earth - moon ), speed in orbit around Sun, rotation over Earth's axis... And add strength of earthquake on piece of paper with all other data... Earthquake force is negligible.

Can you provide some numbers for this? It's not obvious to me that it is negligible at all.

http://www.nature.com/nature/journal/v262/n5566/abs/262259a0.html

twofish-quant
Well I think its a load of codswallop. but the press is reporting this as if its real. For such an event to occur would mean that all the stars would have moved in relation to the earth by a small amount, which means every astronomer would need to recalibrate their equipment.

Which happens all the time. When you are doing microsecond measurements for things like interferometry, you have to take into account a *lot* of stuff.

For most things you don't have to worry about microsecond variations. For the things that you do have worry about, then yes. If you want the gory details about how time works in astronomy pick up The Explanatory Supplement to the Astronomical Almanac

Homework Helper
Not sure quite what your point is.
We can measure changes in the rotation speed of neutrons stars due to star-quakes on their surface, since NS are so dense the movement of the crust needed to make a measurable change in rotation rate is tiny. Ironically we can measure a movement in the surface of a NS with an accuracy less than mm, while only knowing it's distance to an accuracy of 10s of lyr.

The Earth's rotation is changing constantly, there is along term slowdown due to tidal friction with the moon, there are annual variations due to rain and snowfall changing the distribution of the mass and there are slower effects such as the northern hemisphere rebounding from the last ice age. These effects add up to almost a second/year which is why we add leap seconds.
The effect of a large earth quake is measurable but not significant compared to this.

Mentor
So one plate goes below another which means the net result should be approximately zero. eg: one plate falls the nearby plate rises to accommodate it.

Quite unlikely that both effects cancel out EXACTLY.

Mentor
But the Earth's rotation is also slowly slowing down due to tidal friction...anyone have an estimate on that rate, and how the change in rotation speed due to this earthquake is comparable?

I don't remember exact numbers, but I recall information from one of the http://de.wikipedia.org/wiki/Hoimar_von_Ditfurth books that change in a number of days per year can be observed in fossils (diatoms?). Main idea is that the frustule (or shell, or some other solid support) grows in layers and thicknes of these layers changes on a daily basis (day/night cycle) and on a yearly basis (seasons). This allows calculation of number of days per year in the past.

This book is somewhere here, but I have no idea where :grumpy:

Homework Helper

The Chilean earthquake changed the length of a day by something like 0.001 ms, so negligible on the annual scale of changes

Andre
Why not discuss earth things in the earth forums. Then you have alot more chance that questions are answered and errors are corrected.

Mentor
Very cool plot, mgb.

curiouschris
Quite unlikely that both effects cancel out EXACTLY.

hence I used the word approximately. in other words the actual redistribution of weight should be negligible.

Mentor
Obviously if the effect is measurable, redistribution of weight is not negligible.

curiouschris
The trouble is the effect is not measurable. its only an approximaguesstimatation. the minimum that can be measured is 20 milliseconds so yeah its negligible. still that's not the point the main point was about the change in the earths axis. 8cm is negligible on the global scale but on the cosmic scale I am sure its not negligible.

All I wanted to ask was did the earth really move or was it a figment of scientists imagination.

And I am not sure that a sudden change in the earths axis of only 8cm is negligible. Imagine alls the oceans of the world asked to move 8 cm at once. I am pretty certain thats not negligible.

CC

Homework Helper
You can measure rotations changes in the usec range with VLBI, of course the effect of the earthquake is swamped by other earth effects - as the graph shows.

You can even more easily measure figure changes on this scale from RTK-GPS base stations and VLBI baseline corrections.

Staff Emeritus
The trouble is the effect is not measurable. its only an approximaguesstimatation. the minimum that can be measured is 20 milliseconds so yeah its negligible.
Baloney. The residual in dUT1 and LOD are typically on the order of 0.01 milliseconds. See IERS Bulletins A and Bulletin B. A 20 millisecond residual would make a lot of high-precision VLBI applications useless.

All I wanted to ask was did the earth really move or was it a figment of scientists imagination.
Yes, that 8.8 magnitude earthquake was just a figment of scientist's imagination. :uhh:

That 8 cm change is relatively small potatoes compared to the 2 meter or so motion that can occur over the course of about a 435 days to Chandler wobble and a year due to seasonal changes. For example, the amount of snow that falls on Siberia measurably affects the Earth's rotation.

curiouschris

http://news.nationalgeographic.com/news/2010/03/100302-chile-earthquake-earth-axis-shortened-day/
Currently, scientists can measure the length of an Earth day with an accuracy of only about 20 millionths of a second, so the shortened day caused by the Chile earthquake can be estimated but not measured.

I should have said 20 microseconds, not 20 milliseconds.

My concern is a 8cm 'jump' as opposed to a gradual shift would cause massive objects on the earths surface to become unreasonable in their opposition to the change. you can't ask the oceans to reposition themselves by even 8cm in the short period of time that the earthquake occurred in. Try and move a bowl of water suddenly. it sloshes everywhere.

So and I say it again the problem is the report has been misquoted. yes the earths principal axis may have moved. and yes the earth may eventually catch up with that move but no the 'Actual Axis' didn't move by any appreciable amount during the earthquake.

I am glad to see others more reputable than me are now starting to voice their opposition to this claim.

http://www.bild.de/BILD/news/bild-e...cientists-put-planet-earth-back-on-track.html

As I asked in the very beginning one way to verify such a change is to observe the stars, (assuming the earths change in position didn't alter space time in such a way that it dragged the universe around with it [tic])

So again the question is simple did any astronomers have to recalibrate their equipment over and above the recalibration which would be required for the 'known' nutations to account for this supposed shift.

BTW The chandler wobble is impressive. thanks for the heads up on that :)

Last edited by a moderator:
Staff Emeritus
My concern is a 8cm 'jump' as opposed to a gradual shift would cause massive objects on the earths surface to become unreasonable in their opposition to the change. you can't ask the oceans to reposition themselves by even 8cm in the short period of time that the earthquake occurred in. Try and move a bowl of water suddenly. it sloshes everywhere.
You are looking at things wrong. It doesn't help that the lay articles imply that the Earth 'jumped' by 8 cm. That isn't what happened. It wasn't the Earth that moved; it was the Earth's axis.

The conserved quantity of interest is angular momentum. Over the short timespan of an earthquake the Earth's angular momentum will be very, very close to constant. The influence of the Moon and Sun discussed earlier is far too small to have any influence over a shortish period of time. Any short-term changes in the Earth's inertia tensor would necessarily result in a change in Earth's angular velocity.

Any change in the Earth's angular velocity can be broken down into two components, one parallel to and the other normal to the angular velocity vector. In the issue at hand, the 1.26 microsecond change in the Earth's rotation rate is the parallel component and the 8 cm change in the Earth's axis is the normal component. Both of these changes would have a small (immeasurably small) effect. Moreover, while change in the Earth's rotation rate would have the greatest impact at the equator and none at the poles, the change in the orientation would have the greatest impact at the poles and none at the equator.

How big (or rather, how small)? That 8 cm change in the Earth's pole corresponds to 2.6 milliarcseconds. The quake lasted about 3 minutes. The average angular acceleration is 2.6 mas/3 minutes * 360°/day or 1 nanoarcsecond/second2. The apparent force at the South (or North Pole) would be about 3.3×10-9 g or 3.2 microgals. Very tiny!

I am glad to see others more reputable than me are now starting to voice their opposition to this claim.

http://www.bild.de/BILD/news/bild-e...cientists-put-planet-earth-back-on-track.html
Where have those scientists been for the last fifty years? The short-term changes in the Earth's rotation rate and axis result from internal changes, not external. Google the term polar motion.

curiouschris
The apparent force at the South (or North Pole) would be about 3.3×10-9 g or 3.2 microgals. Very tiny!

I am sorry but I don't know what this relates to. no one one claimed the gravity at the poles suddenly became greater or lesser. although of course the shortening of the day is in relationship to the redistribution of mass, which would have moved the earths center of gravity which would have altered the relative gravity at every point on the surface. I think we can agree the amount was negligible, and less so if the subduction was balanced as I contend it should have been (as one plate pushes below, the other plate rises to accommodate it, net effect close to zero. This assumes there was not some void below that allowed the tectonic plate to subduct [slide under] without displacing the other plate).

Also if the axis shifts its a worldwide thingy. You can't say the axis shifting would have the greatest impact at the poles and very little at the equator. If the shift was instantaneous then it would be different at different points on the equator depending on their relative position to the plane of the shift (sorry not sure what else to call it). but that also assumes that the shift rotated around the center of the earth and not some other point.

Still my question remains and I assume its because no one who has responded in this forum is an astronomer (which is why I picked this forum) or no one who is an astronomer is prepared to say (caught in groupthink?).

Another way to think of it. an observer watching the sun would have noticed during that three minute period that the sun had moved relative to him. it may have slowed down or sped up or shifted to another position relative to the horizon with respect to his position on the earth.

Another example, a photographer taking a long exposure of the stars in such a way that the stars smear into lines due to the rotation of the earth, would have noticed an aberration in his photograph. Dependent on his position on the earth, the lines drawn by the movement of the stars would suddenly change direction for a few minutes and then resumed their original path. The path of the stars would be kinked.

Just because someone from NASA or any other scientific organisation says its so doesn't make it so. Thats not science thats religion.

CC

I am aware a milliarcsecond is too small for a human observer to notice. my examples are exaggerations. only there to make a point

Last edited:
Staff Emeritus
The apparent force at the South (or North Pole) would be about 3.3×10-9 g or 3.2 microgals. Very tiny!
I am sorry but I don't know what this relates to. no one one claimed the gravity at the poles suddenly became greater or lesser.
The force an earthquake exerts on an ant is much, much smaller than that exerted on a bridge. Dividing those two very different forces by the masses of the ant and bridge will yield the same common acceleration. It is the acceleration from earthquakes that causes buildings and bridges to topple. Seismometers are very similar to accelerometers in principle; in fact, some seismometers are accelerometers.

I think we can agree the amount was negligible, and less so if the subduction was balanced as I contend it should have been (as one plate pushes below, the other plate rises to accommodate it, net effect close to zero. This assumes there was not some void below that allowed the tectonic plate to subduct [slide under] without displacing the other plate).
A void is not needed here. Just materials of different density. That is exactly what happened with this earthquake. The earthquake was a result of the subduction of the Nazca Plate under the South American Plate. The Nazca Plate is an oceanic plate while the South American Plate is a continental plate. Oceanic crustal material is considerably more dense than continental crustal material.

Also if the axis shifts its a worldwide thingy. You can't say the axis shifting would have the greatest impact at the poles and very little at the equator.
I was wrong there.

Rotating frame dynamics:

$$\mathbf F_{\text{eff}} = \mathbf F_{\text{ext}} - m\boldsymbol{\omega}\times(\boldsymbol{\omega}\times \mathbf r) - 2m\boldsymbol{\omega}\times \mathbf v - \frac{d\boldsymbol{\omega}}{dt}\times \mathbf r$$

The affect in question is the final omega dot cross r term. This is zero when r is parallel to omega dot, maximal when r is normal to omega dot. The affect of the change in the orientation of the axis would be greatest along the lines of longitude normal to the shift and zero along the lines of longitude 90 degrees offset from that to the shift. Along this line of longitude the magnitude of the affect would be constant and purely horizontal were it not for the Earth's equatorial bulge.

If the shift was instantaneous then it would be different at different points on the equator depending on their relative position to the plane of the shift (sorry not sure what else to call it).
I get the feeling you have a picture of the Earth rotational axis being a rod extending through the Earth, and that this axis shift was the equivalent of grabbing that rod and rotating so that the poles moved by 8 cm. That is not what happened. The Earth did not move. The axis of rotation did. Big difference there.

but that also assumes that the shift rotated around the center of the earth and not some other point.
Read up on Euler's rotation theorem.

Another way to think of it. an observer watching the sun would have noticed during that three minute period that the sun had moved relative to him. it may have slowed down or sped up or shifted to another position relative to the horizon with respect to his position on the earth.

Another example, a photographer taking a long exposure of the stars in such a way that the stars smear into lines due to the rotation of the earth, would have noticed an aberration in his photograph. Dependent on his position on the earth, the lines drawn by the movement of the stars would suddenly change direction for a few minutes and then resumed their original path. The path of the stars would be kinked.
Your examples are flawed because of your mental image of the Earth moving. That is not what happened. The axis moved within the Earth. The affect of this change in axis orientation is cumulative rather than instantaneous. If the affect is observable (and that is a big if; we do not have a good physical model of polar motion), seeing the affect of this change will require some time.

ThomasEdison
At risk of derailing the thread, when the rotation of the Earth being affected by snowfall in Siberia was mentioned, I could not help but think about massive solar flares (are there starquakes too?) which happen on the Sun all the time. Wouldn't the Solar flares change the Earths orbit around the Sun by some margin as well as affecting Sun's own spin or give it a wobble? And wouldn't this happen all the time?

Last edited:
curiouschris
I think we are getting somewhere here

I get the feeling you have a picture of the Earth rotational axis being a rod extending through the Earth, and that this axis shift was the equivalent of grabbing that rod and rotating so that the poles moved by 8 cm. That is not what happened. The Earth did not move. The axis of rotation did. Big difference there.

Is the crux of the problem, To a layman (me) that is exactly what the press seem to be saying. that the earth moved in essence the north and south poles are pointing to a position in the sky that is 1.2 millarcseconds different to what it was 3 minutes earlier. in other words the axis (imaginary shaft about which the earth rotates) of the earth had shifted by 8cm.

So then might you be so kind as to explain what you mean by "The Earth did not move. The axis of rotation did" I assume you aren't talking about it rotating around the axis as it does all day long (and some nights) but are talking of some other rotation.

I am afraid I am rather lost though as I can't see other reading of "the earths (principle) axis moved by 8cm" other than now the earths orientation in space is now marginally different to what it was before the earthquake.

I think what you mean, and please explain if I am wrong that what a layman would call the center of gravity has moved, so say assuming the earth was a perfect sphere with consistent density then the centre of gravity would be exact centre of the sphere e.g. 1/2d
But then the earths shaped changed a little such that the centre of gravity is no longer at the centre of the sphere. thus the earth would wobble a bit or more or a bit less than it did prior to the earthquake.

Is that close?

I also read up a little on Euler's rotation theorem and it seemed to me to be a complex way of saying any spheres rotation can be summarised by three points. xy and z. I would assume that the point of intersection of the three axis described by those points is fixed at the center of the sphere. (which I guess technically means 4 points) but I need to spend more time when I am less tired reading about it.

CC

Staff Emeritus
I think we are getting somewhere here

I get the feeling you have a picture of the Earth rotational axis being a rod extending through the Earth, and that this axis shift was the equivalent of grabbing that rod and rotating so that the poles moved by 8 cm. That is not what happened. The Earth did not move. The axis of rotation did. Big difference there.

Is the crux of the problem, To a layman (me) that is exactly what the press seem to be saying. that the earth moved in essence the north and south poles are pointing to a position in the sky that is 1.2 millarcseconds different to what it was 3 minutes earlier. in other words the axis (imaginary shaft about which the earth rotates) of the earth had shifted by 8cm.
Minor correction: The calculated shift was 2.7 milliarcseconds, not 1.2.

Now to the main issue. You are envisioning that for a short enough interval of time, Earth's rotation axis has some fixed orientation with respect to the remote stars. (Obviously over a sufficiently long period that is not true. Google "axial precession.") That mental image is what leads to the conclusion that the Earth as a whole moved.

That mental image is not correct. The correct mental image is that the Earth's angular momentum vector has some fixed (or rather, slowly changing) orientation with respect to the remote stars. Over the course of a short enough period of time the angular momentum will be essentially constant. The three minute long duration of the earthquake is a very short period of time in this regard.

So what does this mean? Examine the relation between angular momentum and angular velocity:

$$\mathbf L = \boldsymbol I \boldsymbol{\omega}$$

This seemingly simple expression is really three equations in one. The angular momentum and velocity, $\mathbf L$ and $\boldsymbol{\omega}$, are vectors. The term in the middle, $\boldsymbol I$ is a 3x3 matrix, the inertia tensor.

Solving for the angular velocity,

$$\boldsymbol{\omega} = \boldsymbol I^{-1} \mathbf L$$

So, if the Earth's inertia tensor suddenly changes such as from an earthquake, the angular velocity vector must change to match to keep the angular momentum vector constant. The Earth's angular velocity vector will point to a different location in the sky.

http://www.cv.nrao.edu/~rfisher/Ephemerides/earth_rot.html
"By the standards of modern astrometry, the earth is quite a wobbly platform from which to observe the sky. The earth's rotation rate is not uniform, its axis of rotation is not fixed in space, and even its shape and relative positions of its surface locations are not fixed. For the purposes of pointing a telescope to one-arcsecond accuracy, we need not worry about shape and surface feature changes, but changes in the orientation of the earth's rotation axis are very important. ..."​

Last edited:
curiouschris
I get the feeling of going around in circles here. Caused by axial perturbation perhaps?

Yes the earth wobbles and the length of a day changes due to the irregular shape of the earth as well as from external forces.

Yes an earthquake can be the cause of some of these changes.

I do not need any one to explain to me the reasons behind this, I do understand.

BUT NONE of these processes cause an 8cm change to occur in a 3 minute time frame. Which is what was widely reported in the press.

My original question was clear enough.

Staff Emeritus
Your original questioning of the claimed result is an argument from incredulity and is also based on a still erroneous interpretation of what happened. The Earth did not move; the Earth's axis moved.

curiouschris
Your original questioning of the claimed result is an argument from incredulity and is also based on a still erroneous interpretation of what happened. The Earth did not move; the Earth's axis moved.

Exactly.

But no one would reply to that. Instead going around in circles. My point was exactly what you said.

IN THE PRESS it was widely reported that the earth DID MOVE! My incredulity was that this was accepted as the TRUTH. No one questioned it. I DID hence my original question.

I do not believe the earth moved, I never said I did and I attempted to point out reasons why it could not have moved and a method to determine whether it did move if against all my sensibilities it did move.

No-one here responded as I expected which was "no it did not physically move but yes it the axis (in my lingo the "centre of gravity") has moved and thus over time the pole will move to compensate". Which I assume would only increase or decrease the wobble.

I also stated that I did not believe the subduction of the tectonic plate during the earthquake would cause anything other than a near zero change to the rotational speed of the globe. and hence the length of the day. I have been corrected on that point in that there is significant differences in densities of the material under the tectonic plates (not something I suspected, I assumed gravity would ensure all densities are similar, otherwise the 'upper' tectonic plate should have settled down and equalised the pressure long ago) and thus its possible and in this case probable that one plate did not displace the other plate to have a canceling effect.

CC

Staff Emeritus
IN THE PRESS it was widely reported that the earth DID MOVE!
So the press misinterpreted some scientific result? Tell me something new! I'll be impressed when the press gets some scientific result of even moderate complexity right.

I assumed gravity would ensure all densities are similar, otherwise the 'upper' tectonic plate should have settled down and equalised the pressure long ago.
That is the key point here. One way to look at the continents is they are piles of relatively low density stuff, mostly granite, afloat atop the higher density mafic material, mostly basalt, that characterizes the oceanic crust.

curiouschris
So the press misinterpreted some scientific result? Tell me something new! I'll be impressed when the press gets some scientific result of even moderate complexity right.
All I wanted was some confirmation that the press got it wrong (and I am positive some scientists deliberately play this game to sensationalise their work. for as you say whats new!)
And if the report WAS CORRECT, proof of that.

That is the key point here. One way to look at the continents is they are piles of relatively low density stuff, mostly granite, afloat atop the higher density mafic material, mostly basalt, that characterizes the oceanic crust.

Now you have confused me. Was I right or wrong in my initial postulation. Yes it was the key point of my argument. if one granite chunk settled down (in the earthquake) another chunk *must* have risen to balance it to maintain equilibrium.

Perhaps the re-balancing is the cause of the latest earthquakes. just somewhat later than I realised.

CC

ViewsofMars
I've read through the comments of this topic and by golly some of it reminds me of a *ting* of something I read elsewhere. :rofl:

Question:I am not a believer in the 2012 myth. But I've been wondering if the recent quake in Haiti and the one in Chile today and the weird weather could be caused by pole shifting. Could the fact that the poles are melting and there is unusually cold weather in other places be a sign of pole shifting?

The answer is a resounding no: if the pole shifted even a small fraction of a degree, all astronomical telescopes would be unable to find or track their sources, and all GPS systems would cease to function. I think if airplanes started crashing everywhere because their navigation no longer works, you would be immediately aware of this. I am interested that the idea of a connection with earthquakes or weather would even come to your mind, since you say that you do not believe the 2012 myth. I guess this shows how much the misconceptions about 2012 have entered the way many people think. Neither polar shifts nor Nibiru nor alignments are happening. Is is very sad when people deny our climate crisis, since evidence is all around us of global warming, but instead worry about nonexistent events like polar shifts or planetary alignments.

David Morrison
NAI Senior Scientist
March 11, 2010