On the correlation between Earth tides and microseismic activity

Abstract

To search for a possible correlation between tidal gravity and the variations of microseismic intensity, seismogravimetric records of microseismic noise using an Askania GS-15 tidal gravimeter have been carried out. Microseismic events above a certain energy level (producing accelerations higher than ±20 μgal) were cross-correlated with tidal gravity variations calculated for the site of observation. The results of the present study indicate that a statistically significant relation exists between tidal gravity and the parameter taken to characterize microseismic activity. In most observational series, the variations of microseismic intensity display both diurnal and semi-diurnal tidal periods. There exists, however, a notable exception (designated as a 'noisy' series) where the diurnal period, owing to the large uncertainty of its determination, is practically not representative. The diurnal and semi-diurnal harmonics in the correlation curve have the same amplitude ratio as the proportion between the combined amplitudes of the corresponding families of the tidal waves. The correlation between tidal forcing and microseismic activity occurs, at least in the given geotectonic situation, nearly in phase with the tidal potential, gravity, dilatation, areal strain and stress. The indicated correlation may possibly be attributed to tidal modulation of the microseismic noise owing to hydrothermal activity in the area under consideration.