We have explored the temporal variability of the seismicity at global scale over the last 124 years, as well as its potential drivers. To achieve this, we constructed and analyzed an averaged global seismicity curve for earthquakes of magnitude equal or greater than 6 since 1900. Using Singular Spectrum Analysis, we decomposed this curve and compared the extracted pseudo-cycles with two global geophysical parameters associated with Earth's tides: length-of-day variations and sea-level changes. Our results reveal that these three geophysical phenomena can be be explained with 90% accuracy, as the sum of up to seven periodic components, largely aligned with planetary ephemerides: 1 year, 3.4 years (Quasi-Biennial Oscillation, QBO), $\sim$11 years, $\sim$14 years, $\sim$18.6 years (lunar nodal cycle), $\sim$33 years, and $\sim$60 years. We discuss these results in the framework of Laplace's theory, with a particular focus on the phase relationships between seismicity, length-of-day variations, and sea-level changes to further elucidate the underlying physical mechanisms. Finally,integrating observations from seismogenic regions, we propose a trigger mechanism based on solid Earth-hydrosphere interactions, emphasizing the key role of water-rock interactions in modulating earthquake occurrence.