What to Expect
Distributed Acoustic Sensing (DAS) re-purposes telecommunication optical fibers as massive, dense arrays of strain sensors. This rapidly developing technology enables recording ground motions for long periods of time across long distances (10’s of km) at high spatial (~1 m) and temporal resolution at frequencies ranging from the mHz to the kHz. Recently, the combination of this novel sensing technique with the use of already existing fiber-optic cable networks has offered an attractive alternative to classical seismological studies. Here, we explore the applicability of DAS using so-called “dark fiber” networks, i.e. subsurface fiber-optic cables that are currently not in use for data transmission and can be re-purposed as sensing arrays. I will present results from a dark fiber experiment carried out near Sacramento, in the Central Valley of California, where we apply ambient seismic noise interferometry approaches to 7 months of DAS passive recordings. First, I will show how DAS can be used to acquire surface-wave energy generated by freight trains with the purpose of imaging the shallow subsurface down to depths of ~500 m. Then, coda-wave interferometry techniques will be applied to ambient seismic noise from a variety of sources to monitor changes in seismic velocity perturbations caused by variations in groundwater table through space and time. These case study shows the potential of DAS deployed on dark fiber for cost-effective investigation of the near-surface, and constitutes an example of the versatility of DAS datasets acquired along the same fiber-optic cable.
Verónica is a postdoctoral research fellow in the Energy Geosciences Division of the Earth and Environmental Sciences Area at LBNL. She obtained a Bachelor Degree in Geology from the Autonomous University of Barcelona (Spain) and a joint M.Sc. Degree in Applied Geophysics from TU Delft (Netherlands), ETH Zurich (Switzerland), and RWTH Aachen (Germany). In 2018, she received a PhD from the University of Cambridge (United Kingdom) in which she investigated the spatio-temporal evolution of a large sedimentary basin in northeast Brazil by means of passive and active seismic imaging, subsidence analysis through well-log data and gravity modeling. She then joined LBNL as a postdoctoral researcher to work in the application of fiber-optic sensing for near-surface imaging. Her research focuses on developing and applying seismic approaches to Distributed Acoustic Sensing (DAS) datasets with the goal of understanding the dynamics of subsurface processes for environmental and energy-related applications.