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Glass fiber cable as a seismograph : Directly put through to the earthquake

A sword of Damocles hangs over the city. Seismologists expect to go to Istanbul soon to be a major earthquake. Tomorrow, but in 100 years could devastate the disaster, the city. Exactly earthquake researchers can't say. But it is certain that in the North Anatolian fault zone, Istanbul, through the shifting of the continental plates, and a great deal of tension built up. The need to unload soon.

that is comparable to that experts fear for San Francisco and Los Angeles. Also there is a "Big One", the last of the devastating earthquake in 1906, is long overdue. Other megacities like Tokyo or Mexico City are at risk of similar scenarios. They are located in seismically active zones. Exact predictions are impossible, because even today, too little is known about what exactly is happening. Which processes actually lead to serious earthquakes, or that the tension deformation of the rock in the slow creep of the depth of discharge, the above are hardly felt?

A new technology that could improve the understanding of the processes. And not only that. Perhaps the process will also help volcano researchers and traffic monitoring: seismology by glass fiber cable.

seismographs are expensive and are only used selectively

Normally, earthquake researchers seismographs or geophones. These are systems in which a mass on a spring suspended from a vessel is surrounded. The substrate, on which the geophone is moved, the mass moves – the stronger, the more violent the vibration is. The relative movements to be measured and thus the direction and Magnitude determined. The devices, however, are expensive and can only be selectively used for example in the range of a warp.

How much better would it be to register the quake on a network of Sensors, which is in particular in densely populated regions in the ground, because you used it so far for something completely different? This is exactly what seismologists before lied to now: you want to measure vibration in the ground, by sending laser signals through fiber – optic cables-cables for telecommunications about of tens of millions of kilometres moved, is particularly dense in the urban, but also in the periphery, and even under the sea.

for almost ten years, fiber-optic cables are used in petroleum Exploration, as well as for the Monitoring of Pipelines or in the aircraft industry, by through sending Laser instead of phone signals. Experts call the DTS and THE – "Distributed Temperature Sensing and Distributed Acoustic Sensing" (local shared temperature or acoustic measurement). The hair-thin cable made of glass be laid together with a Pipeline. It's broken the light in the line resistance and is reflected. On the basis of its run-time meters can be calculated exactly where the Defect occurred. In the case of holes, on the basis of Changes in the material expansion on the temperature in the depth close.

bump to the glass fiber cable could be helpful

For the research on earthquakes the seismologists are lying now come to a very different idea of THE be applied: glass fibers have always a small, single thickening, which are necessary for their normal function is completely irrelevant. But this bump back parts of the laser signal is shot in the glass fiber. If, by vibrations due to Earthquake, roads of thunder, trucks, or other disorders – the glass fiber is moved, compressed or stretched, and this changes the light reflection.

"Self-shifts of a few nanometers, we can read in the Signal," says Charlotte Krawczyk, head of the section of near-Surface Geophysics at the German research centre for Geosciences in Potsdam (GFZ). The seismologists send pulsed laser light in the optical fiber. At various Points along the fiber, the light is reflected. If this Reflection is changing now in a state of a laser pulse to another, researchers know that the line is there as a result of a ground vibration has moved. On the basis of the characteristic of the change, you can read off, in what direction and by how much it has moved.

In the glass fiber cable, a plurality of measuring sensors. A group Krawczyk tried last year to a 1994 laid the telephone line on the Icelandic Reykjanes Peninsula, to take advantage of this. "We were absolutely fascinated by the results," says project Manager Philippe Jousset, also a geophysicist at the GFZ. In a 16-Kilometer-long cable, the researchers had all of the four meters on a measuring point. "We had feared that the tubes are installed in which glass fiber cables, the ground movements may intercept and the fiber itself is not more maps, you might not so good," says Krawczyk. "But that was not the case, we were able to detect our signals, both local, small earthquakes, as well as a remote quake in Japan is wonderful."

Possible quantum leap in earthquake research

be considered a seismograph significantly more sensitive. "But our data had a high level of quality, and, above all, they were almost available in real time," says Philippe Jousset. In addition, the infrastructure for this type of measurement is in many places already exists or can be relatively inexpensive, created – in a density that is a seismograph unthinkable. "This makes the new method very interesting."

seismologists in the US lied Stanford University have carried out in the last two years in the glass fiber network under your Institute similar Tests and were similarly successful. Other research groups around the world have started projects. "If the method proves robust, it would be a quantum leap in earthquake research," says Jousset.

Until then, but will still be a lot of systematic scientific work: "We have now demonstrated that the method works," says Charlotte Krawczyk. "But we have yet to see whether this is also in other geological situations of the case, and whether we can distinguish earthquake clear of unnatural vibrations around through the traffic."

Holds the method to these Tests, the possibilities are endless: It could be significantly less effort for the earthquake danger in a new area to assess and derive what zoning regulations should apply. Maybe you could optimize by using glass fibers, the traffic monitoring. Of volcanoes cables could help to improve the Monitoring of their activity.

In the Rest of the geological upheavals around the globe, though not everywhere, but in a never before achieved width. In particular, the Monitoring in at-risk cities such as Mexico City, Tokyo, Los Angeles and Istanbul would greatly benefit. In the long term, says Krawczyk, if one were to understand the processes thanks to the new method much better, it is not possible to calculate perhaps only in the probabilities for earthquakes, "but more in the direction of earthquake prediction."

it is also Conceivable a Tsunami early warning system

at Least the should predict Tsunamis work better. If the measurements prove also in the case of deep-sea cables than in solid – what would an international Team, including the Krawczyks group as a next test, then you could calculate on the basis of the laser signals on the cable load, water pressure, and so tsunami waves as a result of an earthquake at an early stage and in front of you warn. You do not have to install in many Places in the sea, special measurement buoys for a Tsunami early warning system. In addition, it could be plates of the plate tectonics, the movements of the continental, better explore.

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Roland Knauer

If the seismology holds by the glass fiber on its promise, wouldn't so disappear, the Damocles-swords over the earthquake-prone cities in the world. But at least you could assess the risks better and plan accordingly. By the glass fiber could defuse so those swords perhaps at least a little.

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