  In this work we have discovered that the global seismic activity undergoes a
modulation with the period of 54 min. We assume that the modulation is caused
by the fundamental spheroidal oscillations of the Earth 0S2. The hidden 54-min
periodicity of earthquakes was revealed by analyzing of earthquake catalogs
using the method of epoch superposition and the spectral method. Initially we
discovered some signs of the impact of 0S2 oscillations on the earthquakes
accidentally when searching for an antipodal effect of the strong earthquakes.
Subsequently we found independent evidence in favor of our hypothesis when
analyzing human impact on the seismic activity. Namely, along with the spectral
peak of the seismicity at the frequency of 0.277 mHz (which is clearly of
anthropogenic origin) we found a more powerful peak at the frequency of 0.309
mHz, i.e. on the period of 54 min, which coincides with the period of the
fundamental mode of eigen spheroidal oscillations of the Earth.
