Geologists and seismologists are now actively using technological advances. Seismic sensors, which allow you to track the fluctuations of the crust, are becoming more sensitive and less expensive. Thanks to this, scientists are able to install hundreds and thousands of such devices, however, mostly on land.
But, as
it turned out , you can do without sensors at all, using elements of the network infrastructure located at the bottom of the seas and oceans. Up to the present, the installation of specialized devices under water has been very expensive for scientists - so much so that almost isolated systems are installed in the seas and oceans. Fortunately, they can be replaced - fiber optic cables.
A team led by Giuseppe Mara found that these highways are an excellent alternative to seismic sensors. The fact is that the equipment designed for reliable signal transmission over optical fiber, laid under water, is very accurate. So much so that any seismic activity causes changes in the signal itself.
It turned out this is not now, but in 2016. Then an experiment was conducted, one of the elements of which was a fiber-optic cable laid to the coast of Great Britain. Once the transmitted signal began to give distortions. As it turned out, the cause of the distortion is an earthquake measuring 6 points, the epicenter of which lies under the ocean bed.
Measuring the strength of the distortion, scientists were able to learn some of the characteristics of the earthquake. The most severe distortions were recorded immediately after the onset of the earthquake. After that, it began to fade, respectively, the distortions became less noticeable. Experts understand that the cause of the distortion is an earthquake due to the fact that the strongest vibrations of the earth's crust defended in time from each other. And the distortions of the signal passing through the optical fiber very precisely coincided in time with the peak indicators of the activity of the earthquake.
Moreover, the scientists were able to find out exactly where the epicenter of the earthquake was located - this was understood by the time of the appearance of a distorted signal in two highways that were quite distant from each other.
No other equipment was needed by scientists for finding out all these facts. The situation with the use of seismometers is quite different - they need three to carry out triangulation measurements of an earthquake. The measurement results help to know the characteristics of the earthquake. But since the underwater measurement of seismic activity of the crust is expensive and technically difficult to perform, such work is carried out quite rarely.
If you use fiber, laid on the bottom of the seas and oceans, you can learn about the appearance of even not too strong underwater earthquakes. Confirmation of this was obtained by studying the characteristics of the signal passing through the cable connecting Malta and Sicily. Interference detected by experts, exactly coincided in activity with the peak values of earthquakes in this region.
Now, seismologists are trying to prove that intercontinental highways, laid along the seabed and the ocean floor, can make, if not an alternative, then a rather serious addition to the already existing toolbox of seismologists from all countries of the world. All that is needed to study the characteristics of an earthquake that occurs in a region where a highway is laid is a device that, with a high degree of accuracy, makes it possible to measure the error signal of a highway.
Each line contains a large number of individual channels, which are separated by the wavelengths of the optical signal. In order to more accurately measure the characteristics of earthquakes, scientists will need only one channel with a stabilized signal generator and a meter of the characteristics of the signal at the input and output.
In addition, highways can be used to study noise pollution in the ocean or even to track the migration of marine mammals. Yes, the accuracy of the cable may be lower than professional equipment. But if we take into account the cost of specialized systems, in many cases the use of fiber to carry out such measurements is fully justified.
DOI:
10.1126 / science.aat4458