Distributed fiber-optic sensors monitor micro-earthquakes, strain and temperature in the subsurface

What is it about?

Fracturing processes in the underground can be monitored using fiber-optic cables located in boreholes. Elastic wave fields in the subsurface contain low frequency strain information as well as higher frequency seismic information (micro-earthquakes). A laser system at the surface can be used to turn the optical fiber into an array of a thousand virtual sensors, each independently capturing minute subsurface deformations over time. These strain observations can be combined with temperature measurements to obtain a dynamic description of the state of the subsurface. This paper demonstrates the feasibility of observation and practical analysis.

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Why is it important?

We demonstrate that current distributed fiber-optic sensing systems are sensitive enough to record a significant amount of micro-earthquakes, down to a magnitude of approximately -2. The maximum observation distance between a micro-earthquake's location and the fiber-optic sensing cable is about 500 m. This is large enough to cover nearby boreholes and allows engineers to monitor various subsurface activities.

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