Characterization of the Sos Enattos site for the Einstein Telescope

Abstract

In this work we report the ongoing characterization of the Sos Enattos former mine (Sardinia, Italy), one of the two candidate sites for the Einstein Telescope (ET), the European third-generation underground interferometric detector of Gravitational Waves. The Sos Enattos site lies on a crystalline basement, made of rocks with good geomechanical properties, characterized by negligible groundwater. In addition, the site has a very low seismic background noise due to the absence of active tectonics involving Sardinia. Finally, the area has a low population density, resulting in a reduced anthropic noise even at the ground level. This location was already studied in 2012-2014 as a promising site for an underground detector. More recently, in March 2019, we deployed a new network of surface and underground seismometers at the site, that is currently monitoring the local seismic noise. Most of the energy carried by the seismic waves is due to the microseisms below 1 Hz, showing a significant correlation with the waves of the west Mediterranean sea. Above 1 Hz the seismic noise in the underground levels of the mine approaches the Peterson’s low noise model. Exploiting mine blasting works into the former mine, we were also able to perform active seismic measurements to evaluate the seismic waves propagation across the area. In conclusion we also give a first assessment about the acoustic and magnetic noise in this underground site.

Impact of Schumann resonances on the Einstein Telescope and projections for the magnetic coupling function

“…As a part of site characterization of the Sos Enattos mine for ET [29,30], magnetic field measurements were taken from 5 to 100 Hz in the exceptionally quiet environment inside the unused mine. We use 48 days of data taken from November 14, 2019 to December 31, 2019, using a singleaxis Metronix MFS-06e magnetometer positioned inside the Sos Enattos mine about 200 m below ground level.…”

Seismic glitchness at Sos Enattos site: impact on intermediate black hole binaries detection efficiency

“…In the evaluation of the sites that could host such a third-generation detector, a first estimation of the residual noise has been obtained by evaluating the power spectral density of the seismic noise, during a long data-taking, to assess its median value. Presently two sites remain the candidate to host ET: the Dutch site Terziet, near Maastricht, at the border of Belgium, the Netherlands and Germany [14] and the Italian Sos Enattos (Lula -NU, in Sardinia) [5,15,16].…”

A lower limit for Newtonian-noise models of the Einstein Telescope

“…As explained in the previous section, the knowledge of the seismic field plays a crucial role in the estimation of the expected NN. For this purpose, several seismic stations were installed at the two candidate sites, including temporary sensor arrays and permanent seismometer installations [36,37,38]. The best option to achieve a reliable underground seismic measurement is through broadband tri-axial seismometers in borehole installations [21].…”

“…In the Italian island of Sardinia, the other candidate site, two boreholes have been excavated close to two tentative corner locations (named P2 and P3) of a triangle with 10 km side length, where the first corner is represented by the former Sos Enattos mine [36,37]. At both borehole stations, Nanometrics Trillium-SPH2 seismometers are installed about 250 m underground, complemented by Nanometrics Trillium-120 Horizon seismometers in vault installations at the surface [39].…”