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Our friend Bob Davis has been working on a new version of his DIY Earthquake Detection which monitors magnetic fields to attempt to predict earthquakes. This new design is using UGN3503 hall effect devices and an Arduino. “I came up with this idea over 10 years ago because animals behave strangely before earthquakes. They know something is about to happen. I also know animals can navigate magnetically. If you put baby sea turtles in a pool they will swim east to west. If you add a magnet the will arc around it. “
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May 3rd, 2011
I hate to be so negative, but I can’t see this giving very significant results, even assuming that magnetic field distubances can be used to predict earthquakes in any meaningful way (so far, the data doesn’t support it.)
Those sensors are for measuring much larger magnetic fields. They’re rated for 0-900 Gauss, with a sensitivity of 1mV/Guass (.75-1.75v range). The Earth’s intrinsic field is .3-.6G depending on where you are, and I’m going to have to assume that relevant field changes would be much smaller than the intrinsic strength. Even with careful design of the amp and A/D, the sensor’s inherent noise is rated at 90uV, swamping much of the signal.
June 8th, 2011
[...] magnetic field. From the idea that there may be some relationship with these two things, this experimental earthquake detector was born. [Bob Davis] built this device, which uses an Arduino and several Hall effect sensors to [...]
June 8th, 2011
If this guy wants some more accurate magnetic sensors, he should take a look at these:
http://www.sparkfun.com/search/results?term=hmc5843&what=products
They’re costly as sensors go, but these are accurate to 7 milligauss.
June 8th, 2011
Prediction? Wow, that’s a tall order!
Actually, I think this device may be more useful for quake-related measurements if there was a magnetic pendulum hung in the middle of the circle of Hall sensors. Say, you can measure the magnitude of the quake by the amplitude of the swing and (maybe) you can get some bit of data from looking at *where* it swings to, as in the direction of the first kick. But measuring just the ambient Earth’s magnetic field looks like you’ll be measuring a whole bunch of noise and electrical circuits turned on and off in the neighborhood (if your sensor is THAT sensitive).
I thought the common wisdom was that animals *hear* the tremors better than we do, including smaller precursor tremors. I know common wisdom is often wrong but I also know that the simplest explanation ofter is often correct. Hearing sounds (pardon the pun) much more believable than giving the animals (dogs?) a whole new sense – a magnetic sense.
June 9th, 2011
I agree my device lacks sensitivity. However the perpendicular magnetic fields are sometimes even stronger than the North / South field strength. At 1 mv per Gauss amplified x 100 it is .1 V per Gauss. The Arduino is sensitive to .02 volts per division so the earth’s North South filed would cover 5 divisions.
Baby sea turtles dropped in a pool swim perfectly east to west, and arc around a magnet, animals are magnetically sensitive. The latest research says that ULF – 1 to 5 hertz changes in the stray fields may predict an earthquake. Animals might hear those frequencies too. I also saw some information from Japan that 20-100 KC noise might also predict earthquakes. We really do not know exactly what we are looking for, and at best an 80% prediction rate would not be sufficient to evacuate a city.