The devastation caused by the January 2022 eruption of Hunga Tonga-Hunga Ha’apai volcano (HTHH) in the Tongan archipelago reminded us of the importance of monitoring shallow-sea volcanic activity. Seismic observations are essential for such monitoring, but there were no operational seismic stations in Tonga at the time of the eruption. There are only a few islands near Tongan volcanoes, and installation and maintenance of seismic stations on remote islands are expensive. Seismic observations based on distributed acoustic sensing (DAS) using a seafloor cable may provide a more practical and economical solution. To investigate the potential of this approach, we made preliminary DAS observations for 1 week using the seafloor domestic broadband telecommunications cable in Tonga. DAS equipment was installed at the landing station of the seafloor cable at Nuku’alofa on Tongatapu, the main island of Tonga. To provide reference data, we installed several seismometers on Tongatapu. The DAS data we obtained showed high noise levels in areas of shallow coral reef, but noise levels decreased greatly in deeper water areas, indicating that DAS is suitable for seismic observations of the deep seafloor. We detected many local and regional earthquakes during our week of observation and determined 17 earthquake hypocenters by picking P- and S-wave arrival times from the DAS and onshore seismic data. Although most of these were tectonic events related to the subduction of the Pacific plate along the Tonga trench, several events were detected around the volcanic chain of the Tongan archipelago including one event beneath the HTHH crater, implying that activity at HTHH has continued since the 2022 eruption. The much lower cost of installation of DAS equipment compared to that for pop-up type ocean-bottom seismometers and the ability of DAS systems to monitor seismic activity in real-time make it an attractive option for monitoring the activity of HTHH and other volcanoes near seafloor cables in the Tongan archipelago.

Graphical Abstract

中文翻译：

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使用汤加海底电信电缆通过分布式声学传感监测火山活动

2022 年 1 月汤加群岛洪加汤加-洪加哈派火山 (HTHH) 喷发造成的破坏提醒我们监测浅海火山活动的重要性。地震观测对于此类监测至关重要，但汤加在火山喷发时没有运行的地震台。汤加火山附近的岛屿仅有少数，在偏远岛屿上安装和维护地震台的费用昂贵。使用海底电缆的基于分布式声学传感（DAS）的地震观测可能提供更实用、更经济的解决方案。为了研究这种方法的潜力，我们使用汤加的海底国内宽带电信电缆进行了为期 1 周的 DAS 初步观测。 DAS 设备安装在汤加主岛汤加塔布岛努库阿洛法海底电缆登陆站。为了提供参考数据，我们在汤加塔布岛安装了多个地震仪。我们获得的DAS数据显示，浅海珊瑚礁区域的噪声水平较高，但在较深的水域区域噪声水平大幅下降，这表明DAS适合对深海底进行地震观测。在一周的观测中，我们检测到了许多地方性和区域性地震，并通过从 DAS 和陆上地震数据中选取纵波和横波到达时间来确定 17 个地震震源。尽管其中大部分是与太平洋板块沿汤加海沟俯冲有关的构造事件，但在汤加群岛火山链周围检测到了几起事件，其中包括 HTHH 火山口下方的一个事件，这意味着 HTHH 的活动自 2022 年以来一直在持续爆发。与弹出式海底地震仪相比，DAS 设备的安装成本要低得多，而且 DAS 系统能够实时监测地震活动，这使其成为监测 HTHH 和附近其他火山活动的有吸引力的选择。汤加群岛的海底电缆。

图形概要