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Current Affairs

Undersea telecom cables to be used as earthquake monitoring networks

Date: 30 November 2019 Tags: Miscellaneous

Issue

Fibre-optic cables that make up the global undersea telecommunications network may help researchers assess offshore earthquakes, and hidden geologic structures in the depths of the ocean.

 

Background

 The study describes an experiment which turned a 20 kilometre section of undersea fibre-optic cable into the equivalent of 10,000 seismic stations monitoring quakes along the ocean floor. Researchers  recorded a 3.5 magnitude earthquake, and seismic scattering from underwater fault zones during their experiment.

 

Details

  • Researchers used a technique where a device with components for creating, manipulating and detecting light sent short pulses of laser down the cable, and detected how this was backscattered due to strain in the cable caused by stretching.

  • The researchers then measured the scattering at every two metres of the cable, and turned a 20-kilometre section into 10,000 individual motion sensors.

  • The technique could be used to map a previously unknown fault system, and observe several dynamic tidal and storm-driven processes in the water column above.

  • The technique called Distributed Acoustic Sensing, was earlier tested with fibre-optic cables on land, but can now be used to obtain data on quakes happening under the sea, where few seismic stations exist.

  • The researchers said the new system is sensitive to changes of nanometres to hundreds of picometres for every metre of cable length,  a change happening at the scale of one part in a billion.

  • The scientists hope to use the dense fibre-optic networks around the world, spanning more than 10 million kilometers, on both land and under the sea to measure the sensitive seismic movements on the Earth.

Importance of research

  • It is important to know when and where earthquakes occur and their magnitude. Using seismic-wave velocity data collected from networks of stations around the world, researchers produce and analyze three-dimensional images of the rock through which those waves propagated.

  • The images provide insight into processes that include the convection of slowly deforming rock in the mantle, the movement of tectonic plates, and earthquakes.

  • Nearly all the seismic networks, however, are located on land, which precludes seismologists from getting a complete picture of the planet’s internal churning.

  • Adding instrumentation to the 71% of Earth’s surface covered by oceans would dramatically improve the data density and provide seismologists with close-up, unseen detail of mantle plumes, fault lines, and deep-sea earthquakes.