Study of the Correlations Between Long-Periodic Terrestrial Tides and Occurrence of Earthquakes in the Vrancea Site

Following studies already performed by various authors concerning specific tectonic faults we analyse statistically the possibility that earthquakes in the very active seismological zone of Vrancea (Roumania) may be triggered by the vertical luni-solar tidal oscillations when retaining only the components other than diurnal and semi-diurnal. Our conclusion is that for three of the four leading tides, with periods 18.6 y, 182.62 d, and 13.66 d, the earthquakes occur preferentially during the ascending part of each of the sine oscillation. This property is especially visible for the leading 13.66 d fortnightly wave, and for the 18.6 y wave, for which results are very similar to that of Kilston and Knopoff (1983), who analyzed data related to the San Andreas fault in Southern California. As a complement, we carried out an analysis of earthquake periodicities w.r.t. the variation rate of each of the tides above, given by the half-period sine oscillation, which also leads to interesting possible correlations. This revised version was published online in July 2006 with corrections to the Cover Date.