DAS dataset analysis for reflection imaging with ambient noise in urban areas: Granada, Spain

Summary Distributed acoustic sensing (DAS) is an innovative technology with a great potential for acquiring seismic datasets in urban areas. In this work, we will check the suitability of a DAS dataset acquired in the city of Granada (Spain) for retrieving subsurface reflectivity from ambient noise. The fiber-optic is a pre-existing underground telecommunication cable that crosses the city from Northwest to Southeast. We use 10 hours recording of strain rate in a selected sector of the cable to obtain seismic reflections using the autocorrelation method. The results are constrained by the autocorrelation result of a 24 hours record at a three-component seismic station near the targeted sector. Some cable segments do not show clear reflectivity patterns due to a lack of useful energy in these regions that may be related to a loose ground coupling. However, autocorrelation stacks in some other segments are consistent with the results obtained with the seismic station. This work highlights the usefulness of recording strain rate along with urban fiber-optic cables and the use of ambient noise techniques such as autocorrelation. The retrieved reflectivity information can be used to complete 3D geological models, which are essential for urban development projects.