Browsing by Author "Sobolevskaia, Valeriia"

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    Monitoring Water Level of a Surficial Aquifer Using Distributed Acoustic Sensing and Ballistic Surface Waves
    (Wiley, 2024) Sobolevskaia, Valeriia; Ajo-Franklin, Jonathan; Cheng, Feng; Dou, Shan; Lindsey, Nathaniel J.; Wagner, Anna
    Groundwater resources play an increasingly crucial role in providing the water required to sustain the environment. However, our understanding of the state of surficial aquifers and their spatiotemporal dynamics remains poor. In this study, we demonstrate how Rayleigh wave velocity variation can be used as a direct indicator of changes in the water level of a surficial aquifer in a discontinuous permafrost environment. Distributed acoustic sensing data, collected on a trenched fiber-optic cable in Fairbanks, AK, was processed using the multichannel analysis of surface waves approach to obtain temporal velocity variations. A semi-permanent surface orbital vibrator was utilized to provide a repeatable source of energy for monitoring. To understand the observed velocity perturbations, we developed a rock physics model (RPM) representing the aquifer with the underlying permafrost and accounting for physical processes associated with water level change. Our analyses demonstrated a strong correlation between precipitation-driven head variation and seismic velocity changes at all recorded frequencies. The proposed model accurately predicted a recorded 3% velocity increase for each 0.5 m of head drop and indicated that the pore pressure effect accounted for approximately 75% of the observed phase velocity change. Surface wave inversion and sensitivity analysis suggested that the high velocity contrast in the permafrost table shifts the surface wave sensitivity toward the first 3 m of soil where hydrological forcing occurs. This case study demonstrates how surface wave analysis combined with an RPM can be used for quantitative interpretation of the acoustic response of surficial aquifers.
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    Watching the Cryosphere Thaw: Seismic Monitoring of Permafrost Degradation Using Distributed Acoustic Sensing During a Controlled Heating Experiment
    (Wiley, 2022) Cheng, Feng; Lindsey, Nathaniel J.; Sobolevskaia, Valeriia; Dou, Shan; Freifeld, Barry; Wood, Todd; James, Stephanie R.; Wagner, Anna M.; Ajo-Franklin, Jonathan B.
    Permafrost degradation is rapidly increasing in response to a warming Arctic climate, altering landscapes and damaging critical infrastructure. Solutions for monitoring permafrost thaw dynamics are essential to understand biogeochemical feedbacks as well as to issue warnings for hazardous geotechnical conditions. We investigate the feasibility of permafrost monitoring using permanently installed fiber-optic seismic networks. We conducted a 2-month seismic monitoring campaign during a controlled thaw experiment using a permanent surface orbital vibrator (SOV) and a 2D-array of distributed acoustic sensing (DAS) cables, and observed significant (15%) shear-wave velocity (Vs) reductions and approximately 2 m depression of the permafrost table beneath the heating zone. These observations were validated by time-lapse horizontal-to-vertical spectral ratio (HVSR) analysis from three co-located broadband seismometers. The combination of SOV and DAS provided unique seismic observations for permafrost monitoring at the field scale, as well as a basis for design and development of early warning systems for permafrost thaw.