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Abstract:
With the development of Distributed Acoustic Sensing (DAS), vast telecommunication networks hold the potential to serve as dense seismic sensor arrays. As such, they may facilitate the seismic microzonation as well as exploration and monitoring of utilizable and utilized subsurface volumes at favorable costs – particularly in densely populated areas. However, numerous technical aspects remain under investigation to further maturate this innovative seismological approach.In this study, we investigate how loops of slack fiber affect the results of passive ambient tomography, a particularly appealing exploration approach due to its low footprint. We present results obtained with DAS recordings on both purposefully installed as well as dark telecommunication optic fiber. Sledgehammer blows were recorded on an optic fiber laid out in an urban heating tunnel before and after introducing several loops of slack. Discontinuous wavefronts can be observed once the arclength of the coiled fiber exceeds the gauge length. Similar observations were made on the virtual shot gathers calculated along a 4.5 km long segment of dark fiber along a major road in the city of Berlin, Germany. We present how the results of ambient noise tomography along this linear DAS array are affected by the presence of loops of slack.We conclude that DAS channels recording within a loop of slack can be identified during the data processing and require removal prior to final processing.
