Near-surface Imaging Under Extreme Low Temperature with Zig-zag Shaped DAS Arrays

Summary In recent years, with the development and application of distributed acoustic sensing (DAS) technology, telecommunication fiber-optic cables have been transformed into dense seismic arrays that can carry on continuous acquisition. This provides a prerequisite for ambient-noise-based seismic monitoring for near surface imaging, which relies on the dense sensors and continuous acquisition. However, the spatial distribution of optical fibers is not always linear. By synthetic tests, this study concludes that while both Rayleigh and Love waves are recorded by DAS in zig-zag distributions, separating them is difficult due to single-direction recording. In cold areas, soil changes due to snow thaw pose risks to infrastructure. Field experiments were conducted in Inner Mongolia, China, deploying a 400-meter zig-zag optical fiber. One-week continuous DAS data was collected, and cross-correlation analysis was performed. The dispersion spectrogram inversion method was used to obtain velocity models, revealing significant differences in shallow layer shear wave velocities at different temperatures.