2025-09-29 ペンシルベニア州立大学(Penn State)
＜関連情報＞
- https://www.psu.edu/news/earth-and-mineral-sciences/story/fiber-optic-cables-could-act-early-warning-system-geohazards-study
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025JB031477
分散音響センシングによる漏洩表面波を用いた都市カルスト地質の破砕帯の特徴づけCharacterizing Fractured Zones in Urban Karst Geology Using Leaky Surface Waves From Distributed Acoustic Sensing
Zhinong Wang, Tieyuan Zhu
Journal of Geophysical Research: Solid Earth Published: 09 July 2025
DOI:https://doi.org/10.1029/2025JB031477
Abstract
Urban karst geology poses significant geohazard risks, most notably sinkholes and surface depression stemming from soluble and fractured bedrock that is prone to dissolution and collapse. However, mapping and characterizing these hazards using traditional geophysical surveys in cities is challenging due to dense infrastructure and high levels of human activity. In this work, we demonstrate how distributed acoustic sensing (DAS), deployed via preexisting telecommunication fiber-optic cables, can be leveraged to detect fractured weak zones in a populated setting. By recording traffic noises, we are able to conduct large-scale, cost-effective, and minimally intrusive subsurface investigations. Our workflow integrates ambient noise interferometry with advanced signal enhancement techniques, specifically frequency-wavenumber (F-K) filtering and bin-offset stacking. F-K filtering isolates wavefields traveling in opposite directions to suppress localized noise, while bin-offset stacking further enhances signal coherency by superposing channels with common offsets. The resulting Noise Cross-correlation Functions exhibit unique inverse-dispersion patterns that signify the presence of leaky surface waves generated by a low-velocity half-space. We invert the corresponding dispersion curves to derive a 2D S-wave velocity model, highlighting a prominent low-velocity anomaly indicative of a fractured zone. To confirm the karstic nature of this anomaly, rock physics modeling is employed to estimate spatial variations in fracture density, revealing marked heterogeneity in the fractured zone. Our findings underscore the power of DAS-based ambient noise interferometry for delineating karst features and diagnosing potential sinkhole risks in urban environments. By exploiting widely available fiber-optic networks, this approach significantly broadens the practicality of near-surface geohazard mapping at the city scale.
Plain Language Summary
Sinkholes are large and sudden depressions in the ground, commonly found in areas with karst landscapes, which appear as a common threat. When these sinkholes occur in densely populated regions, they can pose significant risks. However, conducting traditional surveys in urban environments is challenging due to the presence of buildings and constant human activity. Here, we demonstrate the use of distributed acoustic sensing (DAS) with pre-existing telecom fiber-optic cables to record traffic noises. By analyzing traffic noises captured by DAS, we identify unique inverse-dispersion patterns in leaky surface waves—where phase velocities increase with higher frequencies, indicating a distinct low-velocity subsurface structure. Using rock physics modeling, we estimate the spatially varying fracture density of carbonate rocks, further enhancing our understanding of the karstification condition. This study highlights that DAS with pre-existing telecom fiber-optic cables is a potential tool for detecting potential geohazards over the city scale.
Key Points
- Ambient noise interferometry, enhanced with frequency-wavenumber filtering and bin-offset stacking is applied to process urban traffic-noise distributed acoustic sensing (DAS) data
- The inverse-dispersion pattern observed in leaky surface waves is attributed to the presence of a low-velocity half-space
- Rock physics analysis quantifies the karstification of the fractured zone, highlighting the potential of DAS for urban geohazard detection
