Tidal and Non-Tidal Frequencies Found in the Seismicity of California

摘要

The seismicity of California (ANCC catalogue) was tested for the possible tidal and/or non-tidal frequencies. The local maxima of tidal potential were computed as a comparative base using global elastic tidal model of Earth by Wahr-Dehant-Zschau. The imperfect elasticity of the Earth mantle was used. Tidal cycles were defined by the analysis of quasi-periods of tidal potential maxima with comparable lengths. We found semi-diurnal, diurnal, fortnightly, monthly, semiannual, annual, 4.425-years up to 18.6-years long tidal cycles. Ocean tides were not considered.Results of the comparison of tidal cycles and seismicity show that tidal cycles with periods equal or longer than semi-diurnal were found in the catalogue and/or in the sub-catalogues.Besides the tidal diurnal cycle, the daily (24:00 hours) period was found. This wave has stronger influence on the seismicity than the tidal diurnal cycle. Its origin is connected probably with temperature cycles on the Earth's surface. The combination of tidal diurnal cycle and daily (24:00 hours) wave leads to the superimposed wave.The 7-days and 3-months long periods were also found in the seismicity. They correspond to the half-size of tidal periods. In this case, maxima of seismicity or other seismic parameters coincide both with maxima and minima of tidal potential.