Seismic 1/f Fluctuations from Amplitude Modulated Earth's Free Oscillation

We first report that the seismic time-sequence data from around the world, excluding major earthquakes, consistently yield the power spectral density inversely proportional to the frequency f. This is the 1/f fluctuation that appears ubiquitously in nature. We investigate the origin of this 1/f fluctuation based on our recent proposal: 1/f noise is amplitude modulation and demodulation. We hypothesize that the amplitude modulation is linked to resonance with Earth's Free Oscillations (EFO), with demodulation occurring during fault ruptures. We provide partial validation of this hypothesis through an analysis of EFO eigenmodes. Additionally, we outline potential methods for the future verification of our theory relating 1/f fluctuations to EFO.