Kennett B L N
Research School of Earth Sciences, The Australian National University, Canberra, Australian Capital Territory 2601, Australia.
Proc Math Phys Eng Sci. 2022 Feb;478(2258):20210812. doi: 10.1098/rspa.2021.0812. Epub 2022 Feb 9.
Distributed acoustic sensing (DAS) exploiting fibre optic cables provides high-density sampling of the seismic wavefield. Scattered returns from multiple laser pulses provide local averages of strain rate over a finite gauge length. The nature of the signal depends on the orientation of the cable with respect to the passing seismic waves. For local events, the dominant part of the strain rate can be extracted from the difference of ground velocity resolved along the fibre at the ends of the gauge interval. For more distant events the response at seismic frequencies can be represented as the acceleration along the fibre modulated by the wave slowness resolved in the same direction, which means there is a strong dependence on cable orientation. Slowness-frequency representations of the wavefield provide insight, via modelling, into the character of the DAS wavefield in a range of situations from a local jump source, through a regional earthquake to teleseismic recording. The slowness-domain representation of the DAS signal allows analysis of the array response of cable configurations indicating a bias due to the slowness weighting associated with the effect of gauge length. Unlike seismometer arrays the response is not described by a single generic stacking function.
利用光缆的分布式声学传感（DAS）可提供地震波场的高密度采样。多个激光脉冲的散射回波可在有限的测量长度上提供应变率的局部平均值。信号的性质取决于光缆相对于通过的地震波的方向。对于局部事件，应变率的主要部分可从测量区间两端沿光纤解析的地面速度差中提取。对于更远的事件，地震频率下的响应可表示为沿光纤的加速度，该加速度由在同一方向解析的波慢度调制，这意味着对光缆方向有很强的依赖性。波场的慢度-频率表示通过建模，可深入了解从局部跳跃源到区域地震再到远震记录等一系列情况下DAS波场的特征。DAS信号的慢度域表示允许分析光缆配置的阵列响应，表明由于与测量长度效应相关的慢度加权而存在偏差。与地震仪阵列不同，该响应不是由单个通用叠加函数描述的。
