Assuming that earthquakes are governed by solid friction and that the fault plane solutions are known, a simplified model of correlation between the seismicity and a specified component of the tidal stress is proposed. In the case of an earthquake sequence with a uniform time distribution and with a prevailing focal mechanism, a test of statistical significance is derived from a binomial probability distribution.
This interaction model is checked over the aftershock sequence of a magnitude 5 earthquake which occurred within a seismic array in the Pyrenees on 29 February 1980. The tidal stress field, including the ocean tide effect, is computed for this area. The global time decrease of the seismicity is taken into account by a time transformation. In order to deal with the time and space complexity of the stress field, a moving window analysis is used. It is shown that during one 7-day period out of a total of 30 days, a positive correlation appears between earth tides and seismicity, in agreement with the proposed model.