Abstract
Continuous, real-time monitoring of surface seismic activity around the globe is of great interest for acquiring new insight into global tomography analyses and for recognition of seismic patterns leading to potentially hazardous situations. The already-existing telecommunication fiber optic network arises as an ideal solution for this application, owing to its ubiquity and the capacity of optical fibers to perform distributed, highly sensitive monitoring of vibrations at relatively low cost (ultra-high density of point sensors available with minimal deployment of new equipment). This perspective article discusses early approaches on the application of fiber-optic distributed acoustic sensors (DASs) for seismic activity monitoring. The benefits and potential impact of DAS technology in these kinds of applications are here illustrated with new experimental results on teleseism monitoring based on a specific approach: the so-called chirped-pulse DAS. This technology offers promising prospects for the field of seismic tomography due to its appealing properties in terms of simplicity, consistent sensitivity across sensing channels, and robustness. Furthermore, we also report on several signal processing techniques readily applicable to chirped-pulse DAS recordings for extracting relevant seismic information from ambient acoustic noise. The outcome presented here may serve as a foundation for a novel conception for ubiquitous seismic monitoring with minimal investment.
Highlights
Optical fibers have been traditionally designed to propagate confined light over several tens of kilometers with minimum attenuation and distortion
Preliminary research on the use of distributed acoustic sensors (DASs) methods to convert the optical fiber into a dense array of seismometers have been recently reported, generally using dedicated fiber or fiber installed in low noise environments
The DAS systems usually employed in seismography are typically 1-2 orders of magnitude less sensitive than the currently available geophones
Summary
Optical fibers have been traditionally designed to propagate confined light over several tens of kilometers with minimum attenuation and distortion. Among the different existing technologies, Rayleigh scattering combined with optical time-domain reflectometry (OTDR) or optical frequency-domain reflectometry (OFDR) has allowed the development of distributed acoustic sensors (DASs), offering the possibility to monitor vibrations along an optical fiber at readout frequencies in the kHz-range.. Among the different existing technologies, Rayleigh scattering combined with optical time-domain reflectometry (OTDR) or optical frequency-domain reflectometry (OFDR) has allowed the development of distributed acoustic sensors (DASs), offering the possibility to monitor vibrations along an optical fiber at readout frequencies in the kHz-range.3 This unique feature of DAS systems has permitted a significant expansion of the range of potential applications of distributed fiber sensors. IV, we comment on the future challenges that DAS technology has to face for the practical re-purpose of the telecommunication fiber network into a distributed seismograph network, as well as a perspective analysis of the future steps of DAS into the broad field of seismology
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