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Science

Geophysicists Discover How Rocks Produce Magnetic Pulses 72

Posted by Unknown Lamer
from the how-do-they-work dept.
KentuckyFC (1144503) writes "Since the 1960s, geophysicists have known that some earthquakes are preceded by ultra-low frequency magnetic pulses that increase in number until the quake takes place. But this process has always puzzled them: how can rocks produce magnetic pulses? Now a group of researchers has worked out what's going on. They say that rocks under pressure can become semiconductors that produce magnetic pulses under certain circumstances.

When igneous rocks form in the presence of water, they contain peroxy bonds with OH groups. Under great temperature and pressure, these bonds break down creating electron-holes pairs. The electrons become trapped at the site of the broken bonds but the holes are free to move through the crystal structure. The natural diffusion of these holes through the rock creates p and n regions just like those in doped semiconductors. And the boundary between these regions behaves like the p-n junction in a diode, allowing current to flow in one direction but not the other. At least not until the potential difference reaches a certain value when the boundary breaks down allowing a sudden increase in current. It is this sudden increase that generates a magnetic field. And the sheer scale of this process over a volume of hundreds of cubic meters ensures that these magnetic pulses have an extremely low frequency that can be detected on the surface. The new theory points to the possibility of predicting imminent earthquakes by triangulating the position of rocks under pressure by searching for the magnetic pulses they produce (although significantly more work needs to be done to characterize the process before then)."
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Geophysicists Discover How Rocks Produce Magnetic Pulses

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  • by Anonymous Coward

    Science, bitches.

  • piezo effect? With magnetism, electricity can't be far behind. I wonder if that can't start underground coal fires.

    • Without oxygen there can't be a coal fire.
      • FTFWiki:

        Some fires along coal seams are natural occurrences. Some coals may self-ignite at temperatures as low as 40 C (104 F) for brown coal in the right conditions of moisture and grain size. The fire usually begins a few decimeters inside the coal at a depth in which the permeability of the coal allows the inflow of air but in which the ventilation does not remove the heat which is generated.

        Nothing to do with piezo though.

        • FTFWiki:

          Some fires along coal seams are natural occurrences. Some coals may self-ignite at temperatures as low as 40 C (104 F) for brown coal in the right conditions of moisture and grain size.
          The fire usually begins a few decimeters inside the coal at a depth in which the permeability of the coal allows the inflow of air but in which the ventilation does not remove the heat which is generated.

          Nothing to do with piezo though.

          if you consider "less than a meter under the surface" to be underground, then yeah I guess it could happen less than a meter under the surface.

    • by whovian (107062)

      piezo effect? With magnetism, electricity can't be far behind. I wonder if that can't start underground coal fires.

      Probably more like lightning preceeding earthquakes:

      https://www.google.com/search?... [google.com]

  • by korbulon (2792438) on Wednesday June 04, 2014 @11:49AM (#47164813)
    Don't nobody tell ICP.
  • by geekoid (135745) <dadinportland @ y a hoo.com> on Wednesday June 04, 2014 @11:49AM (#47164819) Homepage Journal

    those pulses are clearly a MUTO mating call.

  • Animals? (Score:5, Interesting)

    by OzPeter (195038) on Wednesday June 04, 2014 @11:51AM (#47164825)

    Given that lots of animals are sensitive to magnetic fields, this would also seem to explain them reacting prior to earthquakes.

    • Re:Animals? (Score:5, Insightful)

      by Deadstick (535032) on Wednesday June 04, 2014 @12:07PM (#47164971)

      ...given that they really do react in advance to earthquakes. That lore has been in the "everybody knows" class for millennia, but the observations have an unpleasant habit of being reported after the quake. If my house started shaking right now, I could certainly think of something goofy our Jack Russell Terrorist did an hour ago.

      IIRC, Caltech set up a hotline in the 1980's for people to report anomalous animal behavior, and got a null result...the line would start ringing after the tremor, and there was usually an excuse involving not being near the phone. Perhaps it's time for another try, now that we all have cellphones.

      • Re: (Score:2, Funny)

        by Anonymous Coward

        Jack Russell Terrorist? Has it threatened to commit acts of jihad against the neighborhood cats?

        • by Deadstick (535032)

          No, in his only furball with a cat the cat was definitely the aggressor. However, he's hell on prairie dogs.

          • No, in his only furball with a cat the cat was definitely the aggressor. However, he's hell on prairie dogs.

            I'm loving your auto-correct. LOL.

            • by Deadstick (535032)

              Are you commenting on "Jack Russell Terrorist" or "furball"? Both of them are common terms and can be googled...no auto-correct involved.

      • Re:Animals? (Score:4, Insightful)

        by Nutria (679911) on Wednesday June 04, 2014 @12:17PM (#47165043)

        a hotline in the 1980's for people to report anomalous animal behavior

        The problem is that anomalous is such a vague word. I'm not going to call the University every time my cat does something a bit odd.

        • by Anonymous Coward

          If your cat does something odd so frequently that you wouldn't call in as requested, then we can't use odd cat behavior as a predictor of anything.

      • Jim Berkland [wikipedia.org] used to monitor the classified ads in the newspaper for trends in missing pets. Back when there were newspapers, and they had classified ads.

        And TT Brown [thomastownsendbrown.com] had done some interesting research into geologic piezoelectricy, although Wikipedia [wikipedia.org] only talks about his anti gravity research.
    • When your dog starts pooping east-west it is time to take earthquake precautions
      http://www.pbs.org/newshour/ru... [pbs.org]

    • and the electrical properties of the giza complex as well? It has already been postulated that the pyramids were flooded in order to pressurize the stone, causing it to pulse.

    • I remember reading a story of an "exodus" of fish from the region around New Orleans 3 days before the Katrina disaster. People said you could almost walk across without getting wet for stepping on all the fish. I figured "uh oh, something bad's gonna happen." And even though the storm wasn't tremendously huge -- it created a lot of choking debris and run off that could have hurt the fish. So it seems some kind of early warning was helping them.

      Of course the people and weather specialists were warned with t

  • Why is it that the holes can move but the electrons can't? I thought holes were just places where electrons could be but aren't, so moving holes implies movement of electrons.

    • by bobbied (2522392)

      Why is it that the holes can move but the electrons can't? I thought holes were just places where electrons could be but aren't, so moving holes implies movement of electrons.

      Your description of "holes" is accurate. Understand that this term is used do describe how semi-conductors work and it really means "positive charged area" in some material. "Holes" is just easier to say than "a place where an electron could be but is not" or "Positively charged area".

      • by Anonymous Coward

        Semiconductors are materials, where the conduction band (CB) is within 1-2 eV of the upper edge of the valence band (VB). The moderate distance in energy allows some electrons to be thermally activated, at ambient temperatures, from the VB to the CB. In semiconductors, when an electron makes a transition from the VB to the CB, a "hole" is created in the VB and a highly mobile electron is injected into the VB. Thereby an electron-hole pair is generated. Minerals are materials, where the CB is typically more

    • An N-type semiconductor (think N for negative) has an excessive number of electrons. So, those electrons hop around from atom to atom and you get a movement of negative charge.

      A P-type semiconductor (P for positive) doesn't have enough electrons to go around. So, you get places where electrons aren't, but would like to be (holes).

      In either case, you don't really have electrons moving around - you have charge moving around. Think of a tube, where you insert one ball at the end, and a ball pops out the o
  • The new theory points to the possibility of predicting imminent earthquakes by triangulating the position of rocks under pressure by searching for the magnetic pulses they produce (although significantly more work needs to be done to characterize the process before then)."

    But that will only find certain types of igneous rocks formed underwater peroxy bonds under pressure. Not all rocks under pressure. Still if this type of rock is prevalent enough in a region, it could be useful.

    Also geologists have been calculating rocks under stress using so many methods and observation. The problem is the slippage and failure occur unpredictably. The stress can be estimated. The strain may be observed. At least the surface strain. But the ultimate (or failing) strength of the rock layers is largely unknown.

    • Remember that for the most part, most of the world has at least some igneous inclusions that might make this possible, and that further research may point to other electromagnetic discharges that may be detectible. Also, this does not mean underwater. Rocks formed underwater can only be volcanic, as the rapid cooling due to surrounding water creates the microcrystalline-to-glass consistency that makes up ALL volcanic rock. Igneous, by definition, has cooled slowly over time, allowing for crystal growth (in
  • When I see the word "semiconductor" I think "transistor". I wonder if this discover can lead to a new type of commercially practical semiconductor. Obviously not on the size scale of seismic plates, but perhaps this effect can be created in other materials,now that we know it exists.
    • by Megane (129182)
      Maybe the whole planet could be a computer made out of these geologic semiconductors! (Where have I heard that before? Something about mice and dolphins and fjords...)
  • Friedemann Freund is a man with a lot of ideas.. At Yuri's night at the NASA Ames campus, he demonstrated this magnetic pulse-from-rock by using a dense column of rock and a hydrolic press. He had a saucer sized capactive sensor that was tied to a small microcontroller for remote-sensing/field usage that could detect the change in the electric feild near the rock column as it was compressed. He mentioned that he'd instrumented a fault line. He mentioned that the current released was strong enough to ion

    • by geekoid (135745)

      Except all studies seem to indicate that animals do NOT act any differently before an earthquake. It's all seems to be post hoc, ergo propter hoc reasoning.

      • ..Perhaps I remembered that part wrong, at the very least he would likely have used circumspect languge.. If I see him again, I'll ask.. He did mention that before an earthquake, in places, given enough energy release you can apparently see a flash of light, as all the air above the fault ionizes.. Corona discharge has been known to create ozone..

        Animals freaking out beforehand everywhere is unlikely , however standing right above a fault-line where a sudden discharge of energy may be a different story.

  • by ThatsNotPudding (1045640) on Wednesday June 04, 2014 @01:28PM (#47165719)
    Clever work. I'd go so far as to call it... igneous.

    Tip your wait staff.
  • Since the 1960s, geophysicists have known that some earthquakes are preceded by ultra-low frequency magnetic pulses that increase in number until the quake takes place.

    The pluses would have been more impressive if they decreased in number at some point with anti-pulses. I'm guessing they meant frequency instead of number.
  • This summary made me think of LEDs and earthquake lights. Even if there is light generation, though, I can't imagine that it would be very intense. And then there's the whole "buried under meters of rock" issue.

  • by ctrl-alt-canc (977108) on Wednesday June 04, 2014 @06:35PM (#47167881)
    IAAP (I am a physicist), and my work field concerns also geophysics. TFA is very suspicious for several reasons. I just list the simplest points to understand

    First, there are way too much self references: take for example the first sentence "Rocks, especially igneous rocks, behave as semiconduc- tors under certain conditions". They connect this sentence to four papers previously published by one of the authors (Freund). Nobody else in the scientific world ever verified that rocks are semiconductors ?!? This does not make a good start for the topic they are going to discuss.

    The authors claim that it is more than 50 years that the boundary between earthquakes and VLF emission has been established. Unfortunately this is not true: if it were, seismic network would be composed of radio receivers, they are way cheaper than seismometers. The existence of a connection between VLF emission and earthquakes is still an open question, and there are no conclusive proofs supporting it.
    What we know is that earthquakes are usually not associated to a simultaneous VLF emission, so a theory explaining how earthquake precursors can trigger a VLF emissions should also justify why earthquakes have no VLF emission as well.

    Figure 1 of TFA is a masterpiece of deception: please look at the value range in the graphs showing the computed and measured events: do you still think that the numerical predictions estimated by the authors and the field measurements can be defined "similar" ?!? They only share the same shape, when drawn on very different time and amplitude ranges!

    Summing up, I am afraid that this paper isn't going to be of any help with earthquake prediction...the next, please!
    • TFA says these guys suggest it may be so. I'd say that they're close to postulating a hypothesis.

      The next step will be to see if there is enough evidence to support a theoretical assertion. Then, testing and experimentation can be devised to either support or disprove that theory.

      They're suggesting that the Earth's mantle (silicon with an extremely high percentage of impurities present) may act like a semiconductor (silicon with tiny percentages of specific impurities present), creating a natural Zener

Air is water with holes in it.

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