Detecting Tidal Periodicities of Earthquake Occurrence in Japan Using Spectral Analyses

Abstract The periodicities of earthquake occurrences are critical for understanding the mechanism of earthquake nucleation and triggering, yet it remains a topic of ongoing discussion. Here, we develop an annual spectral averaging method to extract potential periodicities from the Japan Meteorological Agency catalog. Unlike previous methods, such as Schuster’s test or Schuster spectrum methods, our method neither relies on the tidal phase information nor requires prior knowledge of assumed periodicities. We simultaneously identified two tidal periodicities, 12.4 and 24 hr, which are consistent with the semidiurnal lunar tide and diurnal solar tide, respectively. This is the first time that the short periodicity smaller than 24 hr was detected by the spectral analysis method. The presence of 12.4 hr periodicity provides the first compelling evidence for tidal triggering of earthquakes. This study may provide a new view for further exploration into external triggering mechanisms of seismicity.