Preliminary study on data recorded by a 3D distributed acoustic sensing array in the Huainandeep underground laboratory

A three-dimensional distributed acoustic sensing (DAS) array was deployed in the Huainan deep underground laboratory, which locates at a depth of 870 m. The DAS array consists of an optic fiber cable cemented in a horizontal tunnel and an existing mine communication cable in a vertical shaft, which makes three-dimensional recording possible. Analysis on the ambient noise recorded at 870 m underground suggests that the influences of air-pressure, temperature and anthropic activities are much weaker than data recorded on surface. During the one-year observation period, signals of several earthquakes at distances from 47 to 1817 km were identified by eye-scanning. In particular, high quality P wave signal of Madoi earthquake was recorded. The strain-rate waveforms recorded by the DAS and derived from two seismometers' records are consistent with each other, which indicates high fidelity of DAS data. Rayleigh wave signal was identified with the polarization by DAS three-component records and its group velocities were measured with the multiple-taper filtering method. On the other hand, raw records of DAS and seismometer were directly compared to estimate phase velocity. Both group and phase velocities can be used to image seismic structure beneath the site. In summary, the underground laboratory provides a unique quiet site to build 3D DAS array, which provides high-quality data for seismic imaging and monitoring.