Fibre-optic infrastructure could be used to detect earthquakes

The underground networks of fibre-optic cables used to transmit information are unlikely to be associated with earthquake detection efforts. However, during earthquakes, these cables are stretched and compressed by the strain of seismic waves.

These waves cause the elasto-optical effect in the cables: a change in the refractive index of the fibre as the length of the fibre core varies. As a result of the elasto-optical effect on light travelling through the fibre, the amplitude and phase of Rayleigh scattering (scattering of light by particles much smaller than its wavelength) is changed. Thus, by receiving and demodulating Rayleigh backscattering, information about seismic waves can be obtained.

The researchers built a Distributed Acoustic/Vibration Sensing (DAS/DVS) system which takes advantage of the elasto-optical effect to extract useful information about seismic waves from captured and demodulated Rayleigh backscattering. The system has a number of advantages, such as good anti-interference performance, high integration level, and long-distance transmission. It has the capacity to detect an enormous range of frequencies between 10mHz to 20kHz with spatial precision of 3.5mm and detection length up to 40km.

The scientists have since deployed the DAS/DVS system at Mount Zipeng in Heifei, where it was used to detect a magnitude-2.3 earthquake in Dingyuan County; a magnitude-2.7 earthquake in Xuancheng, and a magnitude-6.6 earthquake in the Phillippines, among others.

Previously, researchers from the National Physical Laboratory and Instituto Nazionale di Ricerca Metrologica in Turin, Italy, developed a different technique for detecting underwater earthquakes using existing intercontinental fibre-optic cables.

E&T has previously explored the long search for reliable earthquake detection technology. Researchers have increasingly been turning to existing infrastructure as a possible source of information about coming earthquakes