Earth is observed as never before. Satellites predict the weather, track hurricanes, monitor volcanic ash plumes, and record the changes that humans make on land. However, much of the planet is covered in water, and it is extremely difficult to keep a track of the occurrences beneath the waves. This limits scientists’ ability to identify the underwater seismic events.
In a paper recently published in the journal Science, a group of scientists from the National Physical Laboratory (NPL) and Istituto Nazionale di Ricerca Metrologica (INRiM, Italy) describe how they found a new way to detect earthquakes and other seismic activities with the use of fiber-optic cables that crisscross the ocean floors and carry the global internet and telecom traffic.
The team reported that Giuseppe Marra, a senior research scientist at NPL was piloting an underground cable between two locations in the U.K., where he noticed a small slowdown in signal delivery and traced it to small vibrations bending the light. He then found that the vibrations were caused by a remote earthquake. That gave him the idea of using such cables as seismic detectors.
Marra and his team performed their quake-detecting method on both land and submarine fiber-optic cables. A 79-kilometer cable in southern England detected vibrations from earthquakes originating in New Zealand and Japan. Seismometers measured their magnitude as 7.9 and 6.9, respectively. Other land-based cables in the U.K. and Italy sensed a magnitude of 7.3 earthquake that shook the Iraq-Iran border in November 2017. An underwater cable that stretches from Sicily to Malta sensed a magnitude 3.4 tremor originating from the Mediterranean Sea in September 2017. According to Marra, this seismic detecting method still needs to be tested on longer cables that stretch across the oceans.
Marra said, “Detecting underwater earthquakes is crucial to understanding how our planet works but installing a large array of ocean bottom sensors is a very challenging and expensive task. We have now discovered there is a solution at hand, which relies on existing infrastructure rather than on new installations. A great new tool for research in geophysics and other areas of science. We made the first detection of seismic events whilst running frequency metrology experiments not designed to detect earthquakes. I am delighted to see two scientific areas, frequency metrology, and seismology, meeting in such an unexpected way.”
The researchers discovered that the cables could be used in this way without causing any interruptions to service or without requiring any modification to the cables itself. The only thing required would be to gain access to one of a group of channels at both the ends of a cable and access to a small portion of the cable’s bandwidth. A special laser-based detector would be attached to each end to continually monitor the signal.
The team says that if sufficient cables under the oceans were used as seismic monitors, they could provide them with various types of information such as that used to predict tsunamis or the to better understand global seismic activity to predict volcanism.