Tidal Influence on Volcanic and Seismic Activities
摘要
This paper addresses the controversial open question of tidal triggering seismic activity. Two situations illustrate our methodology, the Fani Maoré volcano seismic catalog (Mayotte) and the seismic catalog of Vrancea area (Romania). We apply the HiCum stacking which accepts irregularly sampled time series, directly applicable to seismic databases. It has been tested on synthetic random catalogs showing its neutrality. For the Fani Maoré volcano, the seismic catalogues are divided in two sub-catalogues corresponding to 6-month periods around the solstices. HiCum is used to evaluate the amplitude and phase of the different tidal components present in the seismic catalogue. Two very interesting signals are present in volcano-tectonic and low-frequency seismic events at P1 and K1 periods. The two waves show a phase opposition between June and December solstices. P1 and K1S correspond to the main declinational waves of the Sun. The amplitude modulation of the sum of this pair of waves corresponds to the product of a carrier wave at (K1 + P1)/2 frequency i.e. the diurnal period S1, and a beat frequency at (K1-P1)/2, corresponding to the tropical year. The S1 and S2 signals are also very clearly present with identical phases for the two sub-periods. It demonstrates the tidal Solar influence in the triggering of seismic events in the Fani-Maore seismic catalogue. We select the RomPlus catalogue of the National Institute of the Earth Physics, Bucharest to analyse Tidal modulation applied to seismic data in the Vrancea area. The HiCum method is applied, on the sequence of events, into a sliding time window of 365 days shifted by 30 days, to determine the amplitude and the phase of the two main semidiurnal tides M2 and S2. The phase obtained is used to resolve the variations of the Schuster test ps and the permutation test pp—values. Our analysis confirms the presence of tidal influences induced by earth tides in intermediate seismic activity through specific characteristics of the variation of the statistical coefficients pS and pP near a medium, intermediate or strong earthquake. The analysis in 3D moving windows of the spatial distribution of the statistical coefficient p allowed us to introduce the concept of “statistical tomography of a seismic area using earth tides”.