We assigned a tidal component phase angle for each event which is computed from the earthquake occurrence time. Then the phase angle distribution was obtained by stacking every angle value in a 360 degree coordinate. Main lunar and solar semidiurnal tidal components M2 and S2 are considered. The phase angle distributions are tested by Permutation test which are introduced for the first time to a tidal triggering study. We compared results with classical Schuster's test. Both tests produce one value, p p for Permutation test and p s for Schuster's test, which represent the significance level for rejecting the null hypothesis that earthquakes occur randomly irrespective of tidal activities M2 and S2 phase distribution are random for the complete data set. However, when we set up a one year window and slide it by 30 d step, significant correlations were found in some windows. As a result of the sliding window, data set systematic temporal patterns related to the decrease of the p p and p s values seem to precede the occurrence of larger earthquakes.

Abstract.A stacking method to detect very weak signals is introduced in this paper. This method is to stack observed data in different well known periodicities according to the astronomical clock since majority geophysical observations are time based. We validated this method by applying it in four different cases. Interactions behind the observed parameters become obviously after it is stacked in two diurnal and semidiurnal tidal periodical waves. Amplitude and phase variations will be also measurable when a sliding windows stacking is used. This could be an important reference to find precursors before some earthquakes and volcanic events, corresponding to attenuations of medium patterns.

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Methane occurrences displaying signatures of a possible abiotic origin had previously been reported in the South‐West Carpathians (Romania). Such an accumulation, at Tisoviţa, was intercepted by a well drilled in an ophiolitic rocks massif, whereas in two other localities—situated tens of kilometres faraway—the concerned methane is released via thermal groundwater outflows that are apparently not associated with any ultramafic products. By using groundwater ionic compositions, corroborated with previously published isotopic (13C‐CH4, 2H‐CH4, 3He/4He) and molecular gas analyses, we assessed in more detail the conjectured abiotic provenance of methane, and quantitatively investigated the hypothesis of a progressive mixing between two, abiotic and thermogenic, methane end‐members. The corresponding geofluids behaviour was modelled by hypothesizing a “concealed” ophiolite serpentinization setting (largely similar to that at Tisoviţa), whose abiotic methane production was “diverted” towards remote discharges at ground surface, via a ~20‐km‐long flowpath supposedly generated by recently operating extensional tectonics.

Abstract:As part of a microclimate study at Ascunsă Cave, Romania, we used Gemini Tinytag Plus 2 data loggers to record cave air temperature variability. At one of the monitoring points we recognized the presence of semidiurnal cycles on the order of a few thousands of a degree Celsius that could be produced under the influence of the semidiurnal tidal components of the Sun (S 2 ) or the Moon (M 2 ). Using a Gemini Tinytag Plus 2 data logger with an external probe we measured core rock temperature and showed that it does not influence the cave air temperature on such short time scales. We thus rejected the possibility that Earth tides, mostly produced by the lunar tidal influence on the Earth's crust, would have had a semidiurnal influence on cave air temperature. Moreover, time series analysis revealed a 12.00-hour periodicity in temperature data, specific for the S 2 , allowing us to assign these variations to the influence of the thermo-tidal action of the Sun. Using the Ideal Gas Law and assuming a constant volume and amount of air, we calculated that a theoretical change in atmospheric pressure of around 40 Pa was needed to produce the temperature changes we observed. This agrees with published values of atmospheric pressure changes induced by the semidiurnal solar component of the thermal tides (S 2(t) ). We thus can assign the observed temperature changes to semidiurnal atmospheric pressure changes (S 2(p) ) induced by the thermal excitation of the Sun. Our study signals the possibility that readily available data from cave monitoring studies around the world could be used in the study of atmospheric tides.Moreover, it appears that Ascunsă Cave acts as a natural meteorological filter on a short time scale, removing the direct thermal influences of the Sun (especially night and day differences) and preserving only the barometric information from the surface.cave atmosphere, thermal tide, semidiurnal, S 2(t) , Romania