Deep underground observation comparison of rotational seismometers

In the observation of seismic rotational motion, fiber-optic seismometers with wide frequency band, high sensitivity and portability have broad application prospects. The performance of fiber-optic rotational sensors is affected by the ambient noise of the observation environment. Therefore, it is of great significance to test the limit of instrument self-noise and verify its teleseismic signal resolution ability in low-noise environment. In the underground tunnel of the discontinued Huainan Panyi-East Coal Mine, which is located at a depth of 848 meters, we carried out a joint deep underground seismic observation. The self-noise and Love wave recording capabilities of four types of rotational seismometers, including molecular-electronic rotational seismometer (R-2) based on electrochemical technology and three types of fiber-optic rotational seismometers (FOS1/FOS2/FOSS), were compared to figure out instrument sensitivity and characteristics. Results indicate that the sensitivity of the fiber-optic rotational seismometer is higher than that of R-2 electrochemical seismometer; the size of fiber-optic seismometer limits the high self-noise of FOS3 six-component seismometer (three translational components + three rotational components); FOS1 and FOS2 fiber-optic seismometers have lower self-noise and Allan deviation, which can effectively record the teleseismic rotational signals with an epicentral distance of about 1000 km, and the waveforms recorded by the two seismometers keep higher coherence. It can be deduced that the deep underground environment can be used to test and compare the self-noise of fiber-optic rotational seismometers, which will help to understand and improve the performance of rotational seismometers in China.