Giuseppe Marra1*, Cecilia Clivati2, Luckett Richard3, Anna Tampellini2,5, Jochen Kronjäger1, Louise Wright1, Alberto Mura2, Filippo Levi2, Stephen Robinson1, André Xuereb4, Brian Baptie3 and Davide Calonico2
National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK. 2I.N.Ri.M., Istituto Nazionale di Ricerca Metrologica, Strada delle Cacce 91, 10135 Turin, Italy. 3British Geological Survey, The Lyell Centre, Research Avenue South, Edinburgh, Scotland, UK, EH14 4AP. 4Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129, Turin, Italy. 5Department of Physics, University of Malta, Msida MSD 2080, Malta.
Measurements of ocean-floor seismic activity are crucial for understanding the interior structure and dynamic behavior of the Earth. However, whilst water accounts for 70% of the planet’s surface, only a small number of permanent ocean-bottom seismometers exists today because of their prohibitively high installation cost. We have shown that existing telecommunication optical fiber cables can detect seismic events when combined with state-of-the-art frequency metrology techniques and the fiber itself is used as the sensing element. We have detected earthquakes over terrestrial and submarine links with length ranging from 75 to 535 km and a geographical distance from the earthquake’s epicenter ranging from 25 to 18,500 km. By using the proposed technique on the existing extensive submarine optical fiber network, which already criss-crosses the seas and oceans and is compatible with frequency metrology techniques, a global seismic network for real-time detection of underwater earthquakes could be implemented without changes to the underwater infrastructure.
“Ultrastable laser interferometry for earthquake detection with terrestrial and submarine cables”,
G. Marra et al, Science,Vol. 361, 6401, 486-490 (2018)