Seismic noise measures for underground gravitational wave detectors

TL;DR

This paper critically evaluates seismic noise measures for underground gravitational wave detectors, highlighting limitations of current methods and proposing more robust, reliable alternatives for site selection based on seismic data analysis.

Contribution

It identifies issues with existing seismic noise metrics and introduces improved methodologies, including median-based measures and adjusted frequency limits, for better site characterization.

Findings

Mode of seismic data is noisy and sensitive to discretization.

RMS at 2Hz is influenced by irrelevant information.

Median-based measures are more robust for seismic noise analysis.

Abstract

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.