Detection of a 13.60611-Day Periodicity in Lunar Seismicity and Its Implications for Earthquake Predictability

We report the detection of a robust 13.60611-day periodicity in lunar seismicity derived from Apollo seismic data using the Seismicity Index S. Spectral analysis reveals a statistically significant peak corresponding to half of the lunar draconic cycle, suggesting a strong physical connection between celestial tidal forcing and seismic activity. The observed spectral peak (~13.333 days) can be interpreted as the observational manifestation of the physically refined value of 13.60611 days after accounting for tidal geometry, phase lag, and spectral resolution effects. This finding provides direct observational evidence supporting the hypothesis that tidal forces play a deterministic role in modulating seismic activity. The results have important implications for understanding earthquake predictability on Earth, suggesting that seismic systems may possess an underlying quasi-periodic deterministic structure.