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Abstract:
Characterizing and monitoring the highly variable near-surface underneath urban areas is crucial for understanding phenomena such as resource distribution and storage potential, changes in hydrological systems, and seismic hazard at the sub-kilometer scale. Our current understanding of the urban subsurface is limited by our ability to image its structure and temporal variations at high resolution using classical geophysical approaches. Distributed Acoustic Sensing (DAS) deployed on unused telecommunication fiber-optic cables (dark fibers) is an attractive alternative to classic seismological studies in urban areas, as it enables continuous recording of the seismic wavefield across long distances (10’s of km) at high spatial (~1 m) and temporal (down to seconds) resolution across a broad frequency range (mHz to kHz). Here, we explore the potential and challenges of using DAS deployed on dark fiber networks for characterizing and monitoring the near-surface beneath urban areas. We will discuss dark fiber experiments conducted in a variety of settings, including several km-long profiles crossing agricultural areas and densely populated centers in California, and experiments conducted within the city of Potsdam (Germany). We evaluate the usability of anthropogenic signals as passive sources for near-surface imaging and monitoring, as well as the potential for active source seismic imaging in complex noise environments. Challenges associated with poorly documented deployment and coupling conditions of dark fiber networks and the large data volumes generated in these studies will also be discussed. Ultimately, we aim at providing insights into the challenges and opportunities of using dark fiber DAS for understanding the urban subsurface.
