Unrecognized origin signals disturbing water-tubes tiltmeters measurements in geodynamic laboratory of SRC in Ksiaz

The harmonic oscillations of water level changes with several hundred nanometers amplitudes and 10-3 [Hz] frequencies are irregularly observed with the water-tube tiltmeter. The effects are observed only by one of four gauges - the one closest to the entrance to underground. The other three gauges of water-tube tiltmeters are situated at the ends of the corridors and are significantly more distant from the entrance to the underground. The atmospheric pressure signals affect level of water in the instrument by inverse barometric effect. The water-tube tiltmeters can register water level variations associated with inverse barometric effects, which were produced by air pressure signals until 10-5 [Pa] magnitude. The amplitude of harmonic oscillations of water level is significantly large and amounts to 1/10 of tidal amplitude, that is 300 to 500 nanometers, which corresponds to 5 x 10-3 [Pa] of air pressure variations. Harmonic oscillations appear irregularly and their time of duration changes from few days until several weeks. The length of atmospheric wave of 10-3 [Hz] frequencies is of 1000 [km] and cannot be explained by any phenomenon from the outside surroundings or the inside of the underground. Resonance frequencies of air column in the hundred meters long underground corridors are of the order of single Hz. Absence of similar signals in measurements from the other three gauges suggests that the harmonic signals are not propagated through the Earth’s solid body but through the atmospheric medium. The observed micro-vibrations of air pressure are very low infrasounds which can be produced in large dimension space of thousand kilometers size. The open question is what is the origin of micro-vibrations registered by the water-tube tiltmeter.