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 Mátra 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 rms2Hz
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.
