The land of California is often shaken by the movements of the earth's crust, so the experimental station for detecting earthquakes was placed here. And, after a year of observations, the developers state that it works better than expected. The peculiarity of the new system is that it is based on conventional fiber, through which the Internet comes to big cities.
In an optical fiber, light moves, reflected from the walls of the cable, and if this environment were the same and not subject to external influences, the signal would always have the same handwriting. In reality, due to the high speed of light, the slightest vibration, cable displacement, etc. create interference. All you need is to supply sensors to track them - in the oil and gas industry, this technology is called "distributed acoustic sensing".
Stanford scientists laid 4, 8 km of fiber in the form of a figure eight underground, installed ultrasensitive laser detectors and launched a continuous signal transmission. Since September 2016, this optoseismic laboratory has recorded 800 earth tremors, from explosions in a local quarry to the devastating earthquake in Mexico this year. More precisely, both earthquakes, although they occurred at a distance of 3220 km from the station.
The accuracy of earthquake measurements with this technology is inferior to traditional seismometers, but its advantage is that the fiber has already been laid in many places. A simple laser detector of light fluctuations in a cable costs less than $ 1 - if installed in tens of thousands, we get a giant passive system for monitoring Earth's activity. And this will not affect the operation of communication systems in any way.
Signal recorded by the Stanford Optoseismic Observatory on September 8 during the devastating earthquake in Mexico