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Would it be possible to scale up an earth field MRI (Magnetic Resonance Imaging) system to scan a building after an earthquake? To see if there is any hidden structural damage.

Details on Earth field MRI: https://en.wikipedia.org/wiki/Earth's_field_NMR

Exampl bench top earth field MRI device http://www.magritek.com/products/terranova/

Earths magnetic field is weak, which means a lower signal noise ratio, but it is very uniform & uniform fields can give 'better' signals (See: http://www.magritek.com/products/terranova/videos/#05 )

I am thinking the coils would need to added during building construction, so that comparison before and after scans can be made. The system would use the earths magnetic field (which is weak but very uniform) + lots of integration (summing of many scans).

Concrete uses about 10% water when it is poured, so contains a reasonable amount hydrogen. The steel reenforcing bar in the concrete will effect the local field. This would be a good thing because if the steel moved or broke because of the quake, then that would affect the signal and indicate there was a change

I don't think a detailed image would be necessary, just creating a signature of the building (each floor) which could be compared before and after the quake.

Thought? Practical issues?

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    $\begingroup$ Welcome on Physics SE :) It is always a good idea to write out abreviations in case someone is not familiar with it. Also, you might want to be a bit more specific in your question about your actual ideas which you seem to have - it might make people more willing to consider the problem :) $\endgroup$ – Sanya Nov 23 '16 at 8:57
  • $\begingroup$ Good call. Will do in the morning $\endgroup$ – DarcyThomas Nov 23 '16 at 9:02
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MRI isn't that useful for the reasons described above.

But it is relatively easy to x-ray large buildings, even very large very solid buildings.

The structure of the Pyramid determined by cosmic-ray absorption.

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MRI machines use strong magnetic fields to make specific types of atoms or molecular bonds resonate. The intensity of the resulting radiation is then measured along a line. By performing this measurement for many different lines, the three dimensional distribution of the specific type of atom or molecular bond can be reconstructed. If you want to know more about how that works, look up "tomography".

Your idea works in theory, but not in practice. The magnetic fields need to be very strong for the radiation to be measurable, so the Earth's magnetic field is not nearly strong enough. That is why medical MRI machines need big expensive magnets to perform measurements on humans, who are much smaller than buildings. An MRI machine as large as a building would be very expensive to build and would also use a lot of power, so it wouldn't be economical.

Another issue is that the magnetic fields need to be finely tuned for MRI machines to work. Usually these machines are set up to measure the presence of hydrogen atoms. If the structural damage that you want to detect has occurred in a material that doesn't have any hydrogen in it, the damage would not be detectable. However, you could design a custom machine that is tuned to the material that you want to investigate.

So let's say you've overcome these two problems. You have all the money that you need and get a custom, building-size MRI machine built. Now you have to explain to everyone who wants to enter the building that they can't bring anything affected by magnetic fields close to the building, let alone inside. Got an iron belt buckle? Sorry buddy, gotta leave that home. You tried to enter the building with your phone in your pocket? Well, all the data has probably been wiped plus it flew out of your pocket, smashing itself against one of the walls.

So yeah, in conclusion: theoretically possible, practically almost impossible, economically infeasible and not very user friendly. I would suggest using an off-the-shelf structural health monitoring system. If you go for x-rays, make sure to get all the people out of your building first, or you're going to need one of those MRI machines to find all of their new tumors ;)

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    $\begingroup$ I thought NMR only worked for nuclei with spin. Thus many materials cannot be fine tuned. $\endgroup$ – CoffeeIsLife Nov 23 '16 at 10:02
  • $\begingroup$ NMR (&MRI) only works on nuclei with spin of an odd number(generally). So regular hydrogen use deuterium no, tritium yes (but at a different resonant frequency). Like wise C12 no C13 yes C14 no. carbon 13 has a different lamor frequency than hydrogen, and is a lot less common, which is why H is normally used in MRI $\endgroup$ – DarcyThomas Nov 23 '16 at 18:01
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    $\begingroup$ @Cornelis-de-Mooij A high field, building sized, MRI would be impractical; however Earth field MRI is a thing ( I have updated my question with details). It has its tradeoffs of course. Any thoughts? $\endgroup$ – DarcyThomas Nov 27 '16 at 8:25
  • $\begingroup$ It definitely is an interesting idea. It would definitely be cheaper, if it can achieve a sufficiently high signal-to-noise ratio on this scale. Comparing signatures would probably work for determining whether any damage has occurred and maybe the extent of the damage could be quantified, but I think localization is important here; presumably you would want to repair the building. $\endgroup$ – Cornelis de Mooij Dec 21 '16 at 12:33

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