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Summary of the long term data taking, related to one of the proposed next generation ground-based gravitational detector's location is presented here. Results of seismic and infrasound noise, electromagnetic attenuation and cosmic muon radiation measurements are reported in the underground Matra Gravitational and Geophysical Laboratory near Gy\"ongy\"osoroszi, Hungary. The collected seismic data of more than two years is evaluated from the point of view of the Einstein Telescope, a proposed third generation underground gravitational wave observatory. Applying our results for the site selection will significantly improve the signal to nose ratio of the multi-messenger astrophysics era, especially at the low frequency regime., Comment: 47 pages, 37 figures

The selection of sites for underground gravitational wave detectors based on spectral and cumulative characterisation of the low frequency seismic noise. The evaluation of the collected long term seismological data in the M\'atra Gravitational and Geophysical Laboratory revealed several drawbacks of the previously established characteristics. Here we demonstrate the problematic aspects of the recent measures and suggest more robust and more reliable methodology. In particular, we show, that the mode of the data is noisy, sensitive to the discretization and intrinsic averaging, and the $rms_{2Hz}$ is burdened by irrelevant information and not adapted to the technological changes. Therefore the use of median of the data instead of the mode and also the modification of the frequency limits of the $rms$ is preferable., Comment: 13 pages, 9 figures

The analysis of long term seismological data collected underground in the M\'atra Mountains, Hungary, using the facilities of the M\'atra Gravitational and Geophysical Laboratory (MGGL) is reported. The laboratory is situated inside the Gy\"ongy\"osoroszi mine, Hungary, 88m below the surface. This study focuses on the requirements of the Einstein Telescope (ET), one of the planned third generation gravitational wave observatories, which is designed for underground operation. After a short introduction of the geophysical environment the evaluation of the collected long term data follows including the comparison of a two-week measurement campaign deeper in the mine. Based on our analysis and considering the specialities of long term data collection, refinements of the performance and evaluation criteria are suggested as well as performance estimation of a possible M\'atra site., Comment: 30 pages, 18 figures

Matra Gravitational and Geophysical Laboratory (MGGL) has been established near Gy\"ongy\"osoroszi, Hungary in 2015, in the cavern system of an unused ore mine. The Laboratory is located at 88~m below the surface, with the aim to measure and analyse the advantages of the underground installation of third generation gravitational wave detectors. Specialized instruments have been installed to measure seismic, infrasound, electromagnetic noise, and the variation of the cosmic muon flux. In the preliminary (RUN-0) test period, March-August 2016, data collection has been accomplished. In this paper we describe the research potential of the MGGL, list the installed equipments and summarize the experimental results of RUN-0. Here we report RUN-0 data, that prepares systematic and synchronized data collection of the next run period., Comment: 24 pages, 16 figures, accepted version