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The ways by which earthquakes could influence the Earth's rotation and, in a reciprocal way, the Earth tides could possibly trigger earthquakes have been investigated by many authors for more than one century.  After summarizing studies ranging among the most prominent ones on the topic, we present an example of statistical results related to tide-earthquakes correlations starting from a database concerning a specific seismic area, the Vrancea fault located in Romania.

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The correlations between seismic activities and tidal periodicities are investigated at three seismic zones: Vrancea (Romania), Bucaramanga (Colombia) and Hindu Kush (Afganistan). The epicenter of earthquake nests distribution is characterized by intermediate-depth. In this paper, we study the influences of the principal lunar and solar semidiurnal tidal components M2 and S2 on seismic activities. The tidal phase is determined by HiCum stacking method according to the earthquake occurrence time and location. The stacking function could be shifted in time and space domain which provides the possibility to evaluate the seismic activities and tidal periodicities at both. The tidal phase distribution was tested by two independent methods Schuster and Permutation. The null hypothesis between seismic activities and selected tidal periodicities is rejected when the statistical p -values obtained by the two tests reach less than 5% level. As a result of the shift stacking function in time axis, a systematic temporal pattern related to the decrease of the p -values seems to be preceding occurrence of the larger earthquakes. A “tidal tomography” map is obtained when stacking function is shifted in 3D geometry following the epicenters distribution.

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In Hungary there are borehole tiltmeters used for monitoring tectonic movements and landslides. These investigations need long time continuous measurements. The Model 722A tiltmeters of Applied Geomechanics Inc. are fastened to the ground by tamped sand in the borehole.  In some cases the boreholes become untight  and it was thought that in this case the ground water seeping into the borehole could loosen the tamped sand causing a bad coupling between the tiltmeter and the ground. It was proved by laboratory test that the ground water and the variation of its level does not change the coupling of the instrument to the ground. In this paper the description of the test made at the Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences and the results of the measurements are given.

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Probably the most significant link between research into Earth tides and seismology is connected with the first attempts to measure the Earth’s effective elasticity using these tides. In 1863 William Thomson (Lord Kelvin) published his famous paper “On the rigidity of the Earth”, which describes how these observation could determine the mean rigidity of the Earth. This current paper sets out to describe some important developments in this common area of study between seismology and earth tide research until the middle of the twentieth century.

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The assessment of the results achieved in our division at the field of physical geodesy is summarised. The studies at the fields of Earth rotation, Earth tides, Earth gravity and the global and regional Earth deformations related to geodesy and geodynamics are presented by citation of the most important publications and dissertations, which cover the history of our institute. The paper ends with the case study related to the newly developed full roving GPS observation strategy.

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The investigation of the stability of large objects, such as towers, buildings, bridges, etc.\ without disturbing the function of the object plays a very important role. This paper deals with the problem how Earth tide waves can be used as input signals for this investigation. Two large objects, the TV tower and the church Kecske in Sopron (Hungary) were chosen for tidal measurements. The results prove that tidal signals can be detected and under special circumstances these signals can be used for health monitoring of large objects.

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The annual wandering of Earth's pole takes place in an area about 200 m2. Within this area, the amplitudes of the displacements due to Earth tide and global meteorological processes do not exceed a few decimetres. Obviously, very precise measuring technique is necessary for the examination of the above phenomena. Nowadays, these are primarily the devices and the methods of cosmic geodesy. From them, on the basis of Ádám (1990) the VLBI (Very Long Baseline Interferometry), and the SLR (Satellite Laser Ranging) are able to show the variations of the pole with periods between one day and one year. The GPS (Global Positioning System) and the developed processing system of VLBI are suitable for the examination of processes within a day.

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In autumn of 1997 two borehole tiltmeters, type AppliedGeomechanics, A722 were installed for monitoring recentmovements of the Mecsekalja fault in Southwest Hungary. Beside the continuous tilt measurements a geodetic network for GPS and electronic distance measurements (EDM) and a levelling line crossing the fault were established. The borehole tiltmeters are continuously recording and the geodetic measurements (GPS, EDM, precision levelling) are repeated twice in a year, in spring and in autumn. This paper presents experiences and results of the tiltmeter measurements and analyses the disturbing effects e.g. earth tide, tilt caused by ground water level variations, precipitation of the surrounding vegetation, etc.  superposed to the tilt signal. The paper shows some of these effects which can use to prove the goodness of the coupling between the instrument and the ground.

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) Van Camp , M. , P. Vauterin 2005 : Tsoft: Graphical and interactive software for the analysis of time series and earth tides . – Computers

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