Analysis of Shallow Wave Propagation Using Distributed Acoustic Sensing Beneath Bern, Switzerland

Abstract:

Understanding the shallow subsurface structure beneath urban environments is essential in order to anticipate potential risks posed by natural hazards. However, existing infrastructure often inhibits the deployment of traditional seismic arrays. Distributed Acoustic Sensing (DAS) technology allows for the use of existing, in-situ telecommunication fibre-optic cables for the purposes of seismic observation, with resolution down to the metre scale. Studies have shown consistency between shallow subsurface models produced using DAS and the results of independent surveys.

Working in collaboration with the SWITCH foundation, we were able to collect seismic data using existing, in-situ fibres beneath Bern, Switzerland. Data acquisition lasted two weeks, with a spatial resolution of 2 m over 6 km of fibre. Real-time data observation showed the movement of sources of anthropogenic noise (e.g. moving vehicles), as well as the propagation of resulting seismic waves.

Following data processing, the range of signals captured is evaluated in the time and frequency domains. The data quality and consistency along the cable are also assessed. We compute seismic noise correlations using existing methods and work towards the production of a local velocity model, derived primarily from surface wave measurements.

Preliminary results demonstrate the efficacy of DAS using existing telecommunication networks, and confirm the ability to capture signals over a broad range of frequencies. Both observed anthropogenic noise and deterministic signals show promise for the determination of local velocity structure in urban environments, with a long-term goal of urban hazard analysis.