As described in great detail in a recent paper on site criteria for the Einstein Telescope [Amann et al (2020)], a site evaluation needs to consider the impact of site conditions on:
- Detector sensitivity
- Detector operation and duty cycle
- Infrastructure lifetime
- Site-quality preservation
- Construction cost
- Socio-economic impact of ET
Site conditions include geological, hydrogeological, and geotechnical conditions and concerns the construction and lifetime of surface and underground infrastructure and societal aspects. There is a direct impact of environmental fields on the sensitivity of a detector. Magnetic fields can couple to magnetic parts of the seismic isolation and suspension system, seismic disturbances can directly couple with test masses through gravitational interaction, or causes noise when scattered light reflects from unisolated parts of the detector, which partially make it back into the main laser beam.