A 2-D orthogonal distributed acoustic sensing (DAS) array designed for seismic experiments was buried horizontally beneath the Kafadar Commons Geophysical Laboratory on the Colorado School of Mines campus at Golden, Colorado. The DAS system using straight fibre-optic cables is a cost-efficient technology that enables dense seismic array deployment for long-term seismic monitoring, favouring both earthquake-based and ambient-noise-based surface wave analysis for subsurface characterization. In our study, the horizontally orthogonal DAS array records ambient noise data for a period of about two months from November 2018 to January 2019. During this time, the array also detected seismic signals from an M_L3.6 earthquake at Glenwood Springs, Colorado, which exhibit opposite signal polarities in the orthogonal DAS section recordings. We derive the transformation matrix for DAS strain measurements in horizontally orthogonal cables to retrieve both Rayleigh and Love wave dispersion information from the single-component DAS signals using the 2-D multichannel analysis of surface waves method. In addition, ambient noise interferometry is applied to long-term DAS noise recordings. Our theoretical derivation demonstrates that Rayleigh and Love wave Green's functions are coupled in the noise cross-correlation functions (NCFs) of DAS receiver pairs. Stacking NCFs over the horizontally orthogonal DAS array can constructively recover the radial Rayleigh wave component but destructively suppress the Love wave component. The multimodal Monte Carlo inversion of the earthquake-based Rayleigh wave and Love wave dispersion measurements and the noise-based Rayleigh wave measurement reveals a 1-D layered structure that agrees qualitatively with geological surveys of the site. Our study demonstrates that although straight fibre-optic cables lack broadside sensitivity, using appropriate DAS array configuration and seismic array methods can extend the seismic acquisition ability of DAS and enable its application to a broad range of scenarios.

中文翻译：

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水平正交分布声感测阵列，用于基于地震和环境噪声的表面波多通道分析

专为地震实验而设计的二维正交分布式声学传感（DAS）阵列水平埋在位于科罗拉多州Golden的科罗拉多矿业学校校园内的Kafadar Commons地球物理实验室下方。使用直光缆的DAS系统是一种经济高效的技术，它能够密集地部署地震阵列以进行长期地震监测，有利于基于地震和基于环境噪声的地表波分析来进行地下特征分析。在我们的研究中，水平正交DAS阵列记录了从2018年11月到2019年1月大约两个月期间的环境噪声数据。在此期间，该阵列还检测到了来自M _L的地震信号科罗拉多州格伦伍德温泉的3.6级地震在正交DAS断面记录中表现出相反的信号极性。我们推导出用于水平正交电缆中DAS应变测量的变换矩阵，以使用表面波的二维多通道分析方法从单分量DAS信号中检索瑞利和洛夫波的色散信息。此外，环境噪声干涉测量法还应用于长期DAS噪声记录。我们的理论推导表明，瑞利和洛夫·波格林的函数与DAS接收器对的噪声互相关函数（NCF）耦合。在水平正交DAS阵列上堆叠NCF可以建设性地恢复径向瑞利波分量，但破坏性地抑制洛夫波分量。基于地震的瑞利波和洛夫波频散测量以及基于噪声的瑞利波测量的多峰蒙特卡罗反演揭示了一维分层结构，该结构与现场的地质调查在质量上是一致的。我们的研究表明，尽管直形光缆缺乏宽面灵敏度，但是使用适当的DAS阵列配置和地震阵列方法可以扩展DAS的地震采集能力，并使其能够应用于广泛的场景。