Abstract: Seismic data are essential for seismological detection of underground structures. However, it is difficult to obtain long-term, high-density continuous seismic data using traditional instruments in extreme environments such as underwater or a plateau. Compared with instrument manufacturers abroad, the development of DAS in China is relatively late. Since 2016, domestic DAS has been gradually applied to petroleum logging and underground structure detection in urban areas. However, there is much less DAS application in extremely harsh environments. After years of collaboration among the Institute of Semiconductors, Chinese Academy of Sciences (CAS) and Institute of Tibetan Plateau Research, scientists from CAS deployed the self-developed DAS in April 2021 for collecting field data in the Tibetan Plateau. During testing, an armored optical cable (deployed both in the water and above ground) was used to record continuous ambient noise data and active source signals. In this study, the ambient noise tomography was applied to DAS data, and a near-surface (less than 70 m deep) S-wave velocity structure along a two-dimensional survey line was obtained in the Yigong Lake in southeastern Tibetan Plateau. This study provided both theoretical and experimental evidence for high-density data collection and underground structure detection in harsh environments.

Key words: distributed acoustic sensing, Tibetan Plateau, Yigong Lake, ambient noise tomography, near-surface structure