Ocean-generated seismic waves are omnipresent in passive seismic records around the world and present both a challenge for earthquake observations and an input signal for interferometric methods for characterization of the Earth's interior. Understanding of these waves requires the knowledge of the depth dependence of the oceanic noise at the transition into the continent. To this end, we examine 80 days of continuous acquisition with distributed acoustic sensor (DAS) system deployed in two deep boreholes near the south-eastern coast of Australia. The iDASv3™ system deployed in a deep borehole at the CO2CRC Otway Project site provides sufficiently high sensitivity and low instrumentation noise for frequencies from 100 mHz to 20 Hz. Analysis of the seismograms and correlation with wave climate allows decomposing the DAS response into microseisms generated by swell from remote storms (0.15 Hz) and local winds (between 0.2 and 2 Hz), and strong body wave energy from large surf breaks at the coast (from 2 to 20 Hz). The depth dependence of the microseisms provides useful insights into the energy partition between the Rayleigh wave modes and may augment conventional kinematic analysis of the sparse surface seismological arrays. Overall, ocean-generated signals at each channel along the borehole are strongly related to the wave climate, so that—with sufficient amount of training data—the passive seismic records on several downhole DAS sensors has a potential for high-precision monitoring of formations surrounding the borehole as well as remote storms in the ocean.

中文翻译：

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井下分布式声学传感提供了对短期海洋地震波场结构的洞察

海洋产生的地震波在世界各地的被动地震记录中无所不在，这既是地震观测的挑战，也是用于表征地球内部的干涉测量方法的输入信号。了解这些波浪需要了解海洋噪声在过渡到大陆时的深度依赖性。为此，我们使用分布式声学传感器 (DAS) 系统进行了 80 天的连续采集，这些系统部署在澳大利亚东南海岸附近的两个深钻孔中。部署在 CO2CRC Otway 项目现场的深钻孔中的 iDASv3™ 系统为 100 mHz 至 20 Hz 的频率提供了足够高的灵敏度和低仪器噪声。0.15 赫兹）和当地风（0.2 至 2 赫兹之间），以及来自海岸大浪的强烈体波能量（2 至 20 赫兹）。微震的深度依赖性为瑞利波模式之间的能量分配提供了有用的见解，并可能增强对稀疏表面地震阵列的传统运动学分析。总体而言，沿钻孔每个通道的海洋产生的信号与波浪气候密切相关，因此，在有足够数量的训练数据的情况下，几个井下 DAS 传感器上的被动地震记录有可能对周围地层进行高精度监测。钻孔以及海洋中的远程风暴。