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Science: Communication cables can not only access the Internet, but also detect undersea earthquakes

Scientific research ship

Recently, seismologists from the California Institute of technology and optical experts from Google have developed a method to detect earthquakes using existing underwater telecommunications cables, which may improve earthquake and tsunami early warning systems around the world.

In the 1980s, telecom companies and the government began to lay these cables. Each cable can span thousands of kilometers. A huge network composed of more than one million kilometers of optical cables is located at the bottom of the earth's ocean. Now, it has become the global network backbone of international telecom companies.

For a long time, scientists have been looking for a way to use these underwater cables to monitor seismic activity. After all, the earth is a blue planet, and more than 70% of the area is flooded. It is very difficult and costly to install, monitor and operate underwater seismometers to track the earth's movement on the seabed, the researchers said, the ideal method is to use the existing infrastructure on the seabed to monitor seismic activity.


Laying cable

Previous efforts to use optical fibers to study seismic activity have relied on the addition of complex scientific instruments or the use of so-called "dark optical fibers", that is, optical cables that are not actively used. 

Now, Zhan Zhongwen, assistant professor of geophysics at the California Institute of technology, and his colleagues have proposed a method to detect the frequency and form of earthquake and wave waves by analyzing the submarine optical cable in operation. They published this method in the journal Science on February 26.

Professor Zhan Zhongwen said: "this new technology can indeed convert most submarine cables into geophysical sensors, and the length of these sensors will reach thousands of kilometers to detect future earthquakes and possible tsunamis."

They believe that this is the first solution for monitoring seabed seismicity and can be implemented globally. It can complement the existing network of ground seismometers and tsunami monitoring buoys, so that seabed earthquakes and tsunamis can be monitored faster in many cases.


Cable type detection of submarine earthquake

On land, various disturbances (such as temperature changes and even lightning strikes) can change the speed and polarization direction of propagation through optical fiber cables. Zhan and his colleagues found that because the temperature in the deep sea remained almost constant and there was little interference, the change from one end of the cable to the other was quite stable over time. 

However, during earthquakes and when storms produce huge waves, the polarization changes suddenly and violently, which makes it easy for researchers to identify such events in the data. 

At present, when an earthquake occurs miles offshore, it may take several minutes for the seismic waves to reach the land seismograph, and even longer for the verification of tsunami waves. 

Using this new technology, the entire length of the submarine cable can act as a single sensor at locations that are difficult to monitor, and the polarization can be measured up to 20 times per second, which means that if the earthquake occurs near a specific area, an alarm signal may be sent to the area that may be affected within a few seconds.


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