Abstract

Distributed acoustic sensing (DAS) is a novel seismic observation system developed in recent years that can realize ultrahigh density observations and has attracted extensive attention in the field of seismology. DAS uses fiber-optic cables as sensing units, which are easy to incorporate with urban telecommunication fiber-optic cables for seismological observations. Compared with seismometers, DAS has the advantages of being rapidly deployed and recyclable, being able to acquire dense observations at low cost, and convenient data collection. In this study, a 5.2 km long telecom fiber-optic internet cable was utilized as a DAS array in an urban area to record ambient noise, and the noise cross-correlation function (NCF) was calculated. There are two different distribution types of ambient noise sources along the cable, regular along-road trucks (Taihe Road) and complex ambient noise, including human activities and traffic sources along and across the Jinniu road. In the first case, we constructed a 2D S-wave velocity model down to 100 m depth and a low-velocity zone was revealed. The S-wave model well explained the traffic signal along the Taihe road and the low-velocity zone is also consistent with the results obtained from co-located geophone arrays. In the second case, due to the complexity of the traffic noise distribution, empirical Green’s functions were barely achieved. Therefore, we performed a synthetic test obtaining different NCFs with different source distributions, and two specific cases that dominate the NCF results were matched. Finally, we obtained the traffic noise distribution along the road, which is consistent with the power spectra density of the ambient noise. In conclusion, by combining DAS and urban fiber-optic internet cables with urban traffic noise, we can effectively reveal the traffic activities and image shallow structures with high resolution, which could offer a reference for urban construction and disaster prevention.

Article Highlights

• DAS turns the urban fiber-optic internet cables into ultra-dense permanent seismic observation arrays

• We revealed a high-resolution shallow structure using urban fiber-optic internet cables

• We obtained the distribution of traffic activities along the road

中文翻译：

---

用光纤互联网电缆在城市地区感知浅层结构和交通噪声

摘要

分布式声学传感（DAS）是近年来发展起来的一种新型地震观测系统，可实现超高密度观测，在地震学领域引起了广泛关注。DAS 使用光纤电缆作为传感单元，易于与城市电信光纤电缆结合用于地震观测。与地震仪相比，DAS具有部署迅速、可循环利用、低成本获取密集观测、数据采集方便等优点。本研究利用5.2公里长的电信光纤网线作为城市区域的DAS阵列记录环境噪声，并计算噪声互相关函数（NCF）。沿电缆有两种不同分布类型的环境噪声源，常规沿线卡车（太和路）和复杂的环境噪声，包括金牛路沿线和横穿的人类活动和交通源。在第一种情况下，我们构建了一个深度为 100 m 的二维 S 波速度模型，并揭示了一个低速区。S波模型很好地解释了太和路沿线的交通信号，低速区也与共址检波器阵列获得的结果一致。在第二种情况下，由于交通噪声分布的复杂性，经验格林函数几乎没有实现。因此，我们进行了综合测试，获得具有不同来源分布的不同 NCF，并匹配了主导 NCF 结果的两个特定案例。最后，我们得到了道路沿线的交通噪声分布，这与环境噪声的功率谱密度一致。综上所述，将DAS与城市光缆与城市交通噪声相结合，可以有效地揭示交通活动，并以高分辨率对浅层结构进行成像，可为城市建设和防灾提供参考。

文章重点

• DAS 将城市光纤互联网电缆变成超密集的永久地震观测阵列

• 我们揭示了使用城市光纤互联网电缆的高分辨率浅层结构

• 我们得到了沿路交通活动的分布