Distributed acoustic sensing (DAS) is a new method that measures the strain change along a fiber-optic cable and has emerged as a promising geophysical application across a wide range of research and monitoring. Here we present the results of DAS observations from a submarine cable offshore Cape Muroto, Nankai subduction zone, western Japan. The observed signal amplitude varies widely among the DAS channels, even over short distances of only ~ 100 m, which is likely attributed to the differences in cable-seafloor coupling due to complex bathymetry along the cable route. Nevertheless, the noise levels at the well-coupled channels of DAS are almost comparable to those observed at nearby permanent ocean-bottom seismometers, suggesting that the cable has the ability to detect nearby micro earthquakes and even tectonic tremors. Many earthquakes were observed during the 5-day observation period, with the minimum and maximum detectable events being a local M1.1 event 30–50 km from the cable and a teleseismic Mw7.7 event that occurred in Cuba, respectively. Temperature appears to exert a greater control on the DAS signal than real strain in the quasi-static, sub-seismic range, where we can regard our DAS record as distributed temperature sensing (DTS) record, and detected many rapid temperature change events migrating along the cable: a small number of large migration events (up to 10 km in 6 h) associated with rapid temperature decreases, and many small-scale events (both rising and falling temperatures). These events may reflect oceanic internal surface waves and deep-ocean water mixing processes that are the result of ocean current–tidal interactions along an irregular seafloor boundary.

分布式声学传感（DAS）是一种新的方法，可测量沿光纤电缆的应变变化，并且已在广泛的研究和监测中成为有前途的地球物理应用程序。在这里，我们展示了来自日本西部南海俯冲带室户角海角近海海底电缆的DAS观测结果。即使在仅约100 m的短距离内，在DAS通道之间观察到的信号幅度也有很大差异，这很可能是由于沿电缆路线进行的复杂测深所致的电缆-海底耦合差异。但是，DAS耦合良好的通道处的噪声水平几乎与附近的永久性海底地震仪所观察到的噪声水平相当，这表明该电缆具有检测附近微地震甚至构造震颤的能力。在为期5天的观察期内观察到许多地震，可检测到的最小和最大地震分别是距离电缆30–50 km的局部M1.1事件和在古巴发生的远程地震Mw7.7事件。在准静态，亚地震范围内，温度似乎比实际应变对DAS信号施加了更大的控制力，在该范围内，我们可以将DAS记录视为分布式温度感测（DTS）记录，并检测到许多沿温度方向迁移的快速温度变化事件电缆：少数与温度快速下降相关的大型迁移事件（6小时内可达10 km），以及许多小型事件（温度上升和下降）。