4400 km long: Active subsea cable used for earthquake measurement
A research group has used an active subsea cable to measure seismic tremors on the Pacific seabed. Political obstacles now loom.
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A research group has achieved another milestone in using existing fiber optic infrastructure for early warning and measurement of earthquakes, measuring several events on a 4400 km long subsea cable. The US science magazine Science reports, citing the group that has also published their work in advance. According to the report, the team succeeded in using the active subsea cable between California and Hawaii as a measuring instrument in the summer, equivalent to more than 44,000 seismic stations spaced 100 meters apart. This allowed them to detect an extremely strong earthquake in Kamchatka, the faint traces of a tsunami, and numerous smaller events. The potential is enormous, and the measurements do not interfere with the normal data transmitted.
Parallel to normal data
As with previous attempts, the work now presented also used a method called “Distributed acoustic sensing.” In this method, a measuring device sends light pulses through the fiber optics of the cable. These light pulses generate backscatter that can be measured optically and changes when the cable is stretched – for example, due to seismic activity. Thanks to computer support, these reflections could now also be received from the most distant areas of the cable. In principle, this created a dense two-dimensional network of transoceanic seismometers, Science writes. The signals use higher frequencies than normal data traffic, which is why the method can be used on existing cables.
With this method, it would be possible not only to detect the first tremors that can trigger a dangerous tsunami in undersea earthquakes but also to better explore the Earth's interior, the magazine further writes. Additionally, it could be used to track whale movements and measure ocean currents. Even the movement of continental plates could be investigated this way, without the need to install measuring stations all over the world. “The sensors are there and ready,” Science quotes geophysicist Vala Hjörleifsdóttir, who was involved in the research: “They are just waiting for us to ask them what they see.”
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Now that the fundamental technical questions are likely resolved, other obstacles could prevent global implementation, seismologist Andreas Fichtner from ETH Zurich believes. For example, the military might object because the sensors could also track submarines, Science quotes him. Telecommunications companies that lay the cables might object to the use of the technology for security reasons, as they would rather not disclose the exact locations of the cables. If scientists could use the infrastructure but only after signing non-disclosure agreements, it would be difficult to reproduce the results. Logistical and political obstacles could therefore now be too high.
(mho)
