Observation and research of deep underground multi-physical fields—Huainan −848 m deep experiment

Abstract

Compared with the surface, the deep environment has the advantages of allowing “super-quiet and ultra-clean”-geophysical field observation with low vibration noise and little electromagnetic interference, which are conducive to therealization of long-term and high-precision observation of multi-physical fields, thus enabling the solution of a series of geoscience problems. In the Panyidong Coal Mine, where there are extensive underground tunnels at the depth of 848 m belowsea level, we carried out the first deep-underground geophysical observations, including radioactivity, gravity, magnetic, magne-totelluric, background vibration and six-component seismic observations. We concluded from these measurements that (1) the background of deep subsurface gravity noise in the long-period frequency band less than 2 Hz is nearly two orders ofmagnitude weaker than that in the surface observation environment; (2) the underground electric field is obviously weaker thanthe surface electric field, and the relatively high frequency of the underground field, greater than 1 Hz, is more than two orders of magnitude weaker than that of the surface electric field; the east-west magnetic field underground is approximately the same asthat at the surface; the relatively high-frequency north-south magnetic field underground, below 10 Hz, is at least one order ofmagnitude lower than that at the surface, showing that the underground has a clean electromagnetic environment; (3) in additionto the high-frequency and single-frequency noises introduced by underground human activities, the deep underground spacehas a sig-nificantly lower background vibration noise than the surface, which is very beneficial to the detection of weakearthquake and gravity signals; and (4) the underground roadway support system built with ferromagnetic material interferesthe geomagnetic field. We also found that for deep observation in the “ultra-quiet and ultra-clean” environment, the existinggeophysical equipment and observation technology have problems of poor adaptability and insufficient precision as well asdata cleaning problems, such as the effective separation of the signal and noise of deep observation data. It is also urgent tointerpret and comprehensively utilize these high-precision multi-physics observation data.

Six‐Component Earthquake Synchronous Observations Across Taiwan Strait: Phase Velocity and Source Location

“…Since the estimation of phase velocity and source location both rely on observing records with high SNR, it is necessary to further improve the sensitivity of fiber‐optic rotational seismometer. On the other hand, decreasing the environmental noise through methods such as deep underground observation is also a significant approach to improve SNR of rotations (Chen et al., 2022; Simonelli et al., 2016; Wang et al., 2023).…”

“…Simonelli et al (2018) positioned a large ring laser gyroscope in a deep underground environment, within the Gran Sasso National Laboratories, and collected dozens of events. Wang et al (2023) carried out earthquake observation in the Huainan Deep Underground Lab (HDUL) at 848 m underground, confirming that deep underground has lower environmental noise and is suitable for high-precision earthquake observation. Chen et al (2022) compared and test various fiber-optic rotational seismometers in HDUL, and recorded the Love wave excited by a teleseismic event.…”

“…Wang et al. (2023) carried out earthquake observation in the Huainan Deep Underground Lab (HDUL) at 848 m underground, confirming that deep underground has lower environmental noise and is suitable for high‐precision earthquake observation. Chen et al.…”

Long Short-Term Memory Recurrent Network Architectures for Electromagnetic Field Reconstruction Based on Underground Observations

“…Since 2020, collaborative observations of multigeophysical fields have been conducted at the Huainan underground laboratory (HNLab) in China. These observations highlight the advantages and potential of the underground environment for sustained, stable geophysical field measurements [13][14][15][16][17][18][19]. However, geophysical fields observations in HNLab are still in the early stages [16], and numerous challenges remain, including experimental method design, underground lab infrastructure renovation, and instrument research and development.…”

Application of Geomechanical Classification Systems in a Tourist Mine for Establishing Strategies within 3G’s Model

“…A significant step towards sustainable mining is the non-traditional use of underground mines and surrounding land [24], such as energy storage [25,26], domestic and industrial waste disposal [27], parking systems in vertical wells [28,29], scientific experimentation facilities [30], underground agriculture [31], underground ecological cities [32], and rehabilitation of underground mines for tourism and recreational purposes [33].…”