Seismological methods have been widely used to construct subsurface images in urban areas, for both seismological and engineering purposes. However, it remains a challenge to continuously operate a dense array in cities for high‐resolution 4D imaging. In this study, we utilized distributed acoustic sensing (DAS) and a 5.2 km long, L‐shaped, telecom, fiber‐optic cable to record the wavefield from a highly repeatable airgun source located 7–10 km away. No P‐wave signal was observed, but the S‐wave signal emerged clearly on the shot‐stacked traces, and the arrivals were consistent with collocated geophone traces. Because the signal quality is significantly affected by cable coupling and local noise, three methods can be employed to improve signal‐to‐noise ratio: (1) stacking contiguous, colinear channels to increase effective gauge length, (2) connecting multiple fibers within a single conduit and stacking collocated channels, and (3) using engineered fiber. In conclusion, the combination of DAS, using internet fiber and an airgun source with proven efficient signal enhancement methods, can provide frequent snapshots of the near surface across an urban area.

中文翻译：

---

在城市地区使用大容量气枪源和Internet光纤进行分布式声学传感

为了地震学和工程学目的，地震学方法已被广泛用于在城市地区构造地下图像。但是，在城市中连续操作密集阵列以进行高分辨率4D成像仍然是一个挑战。在本研究中，我们利用分布式声学传感（DAS）和5.2 km长的L形电信光纤电缆记录了位于7-10 km外的高度可重复的气枪源的波场。没有观察到P波信号，但是S波信号清晰地出现在炮弹堆积的迹线上，其到达与并列的检波器迹线一致。由于电缆耦合和局部噪声会严重影响信号质量，因此可以采用三种方法来改善信噪比：（1）堆叠连续的共线通道以增加有效线规长度，（2）在单个导管内连接多根光纤并堆叠并置的通道，以及（3）使用工程光纤。总而言之，DAS的结合使用互联网光纤和气枪源以及经过验证的有效信号增强方法，可以提供整个城市近地表的频繁快照。