Fibre-Optic Strain Sensing: Game Changer in Seismic Surveying?

Charlotte M. Krawczyk*1, Philippe Jousset1, Thomas Reinsch1

1GFZ German Research Centre for Geosciences, Telegrafenberg, D-14473 Potsdam, Germany (lotte@gfz-potsdam.de).

Natural hazard prediction and efficient crustal exploration benefit from densely designed surveys.  Seismological techniques provide ground-motion data, while active seismics aims at structural imaging and increasingly on physical properties, too. Dense networks exist on some volcanoes and in exploration plays, but not globally.

We demonstrate that dynamic strain determination is now possible with conventionalfibre-optic cables deployed for telecommunication.  This is a new tool for earthquake location, for crustal exploration using unexpected sources, and it provides key records for understanding earthquake and fault structure and dynamics.

On Reykjanes Peninsula, Iceland, we recorded seismic signals from natural and man-made sources with 4-m spacing along a 15-km-long fibre-optic cable layout.  Extending recently distributed acoustic sensing (DAS) studies, we provide spatially un-aliased broadband nano-strain data.  With unprecedented resolution structural features like normal faults and dykes are identified in the Reykjanes rift system, allowing to infer new fault dynamic processes.  Comparison with conventional seismometer recordings corroborates dynamic and stable spectral amplitudes between 0.1-100 Hz bandwidth.

If this workflow proved stable, the use of fibre-optic telecommunication networks worldwide would open a new window for Earth exploration.  We anticipate that monitoring of underground explosions in the framework of the CTBTO, volcano monitoring, hazard assessment and monitoring, and global seismology using transatlantic cables could benefit from such types of technology.  We may also envisage experiments to compare new instrument development in rotational seismology and detailed studies of Rayleigh wave properties.  Other applications (regarding e.g., city underground, car traffic, theft protection) will likely develop for further societal benefit.

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