Julien Pacaud
Beneath the winding streets of Istanbul, Turkey, a fibre-optic cable pulses with laser light. Until recently, this stretch of the information superhighway has lain dormant and dark, but a group of researchers now huddles around to watch a computer screen fill with shimmering lines of data as the light flashes underground. The lines represent subtle underground vibrations from an earthquake, detected along the fibre in a way that has only recently become possible – part of a decades-long quest to peel back the surface of Earth and look inside.
Much of the internet, phone systems, television and other high-speed communications relies on a world-girdling network of fibre-optic cables. By one estimate, more than 4 billion kilometres of such cables snake beneath and between cities; the longest ones span oceans. Normally, we don’t think much about this physical network, happy just to receive the calls, web pages and cat videos it transmits. But more and more, the cables themselves are becoming a valuable source of information about the planet.
In Istanbul, these fibres have revealed potentially life-saving information about how to protect people and infrastructure against future earthquakes. Elsewhere, they are allowing researchers to measure the subsurface hum of London’s bustle, track the rumbling of Iceland’s volcanoes and map the upper reaches of our planet’s mantle. This new view of the underground has the potential to transform our…
