Characterization of the seismic environment at the Sanford Underground Laboratory, South Dakota

Abstract

An array of seismometers is being developed at the Sanford Underground Laboratory, the former Homestake mine, in South Dakota to study the properties of underground seismic fields and Newtonian noise, and to investigate the possible advantages of constructing a third-generation gravitational-wave detector underground. Seismic data were analyzed to characterize seismic noise and disturbances. External databases were used to identify sources of seismic waves: ocean-wave data to identify sources of oceanic microseisms, and surface wind-speed data to investigate correlations with seismic motion as a function of depth. In addition, sources of events contributing to the spectrum at higher frequencies are characterized by studying the variation of event rates over the course of a day. Long-term observations of spectral variations provide further insight into the nature of seismic sources. Seismic spectra at three different depths are compared, establishing the 4100-ft level as a world-class low seismic-noise environment.

Low-frequency terrestrial gravitational-wave detectors

“…Using the seismic spectrum published in [55] and a fit to the pressure spectrum published in [50], we obtain the NN curves presented in Figure 9. As a final remark we want to point out that both seismic and infrasound NN have lower limits since seismic and infrasound spectra both lie above global low-noise models [56,57].…”

The Sanford Underground Research Facility at Homestake

“…Neutrinoless doubleSurface, 800L, [24,25] Demonstrator beta decay using Ge 4850L Center for Ultra-low Bkgd Low-bkgd counter, Surface, 800L, [12,19,20,26] Experiments in the Dakotas isotope separation; 2000L, 4550L, (CUBED); also Bkgd also bkgds: muon, 4850L Characterization neutron, gamma, radon Berkeley Low-Bkgd Facility Low-bkgd counter 4850L [27] Compact Accelerator System Neutron bkgds 4100L, 4850L [28] for Performing Astrophysical Research (CASPAR) Long-Baseline Neutrino Cleanliness tests Surface, 4850L [29] Facility (LBNF) Deep Underground Gravity Seismic characterization Surface, 4850L, [30,31] Laboratory (DUGL) for gravity-wave 300L, 800L, 1700L, research 2000L, 4100L…”

Terrestrial Gravity Fluctuations

“…The last means that amplitude decreases over relatively short distances to the surface. Seismic measurements have been carried out in boreholes [63, 153], and specifically in the context of site characterization for future GW detectors at former or still active underground mines [89, 27, 127, 28]. There are however hardly any underground array measurements to characterize the seismic field in terms of mode composition.…”

“…Underground seismicity above a few Hz is generally very small approaching the global low-noise model. Variations can however be observed, and have in some cases been identified as anthropogenic noise produced underground [89]. Therefore, it is important to evaluate how much noise is produced by the underground infrastructure that is either already in place, or is brought to the site for the underground experiment itself.…”

“…It is evident though that a model-based prediction of the performance of coherent noise cancellation schemes is prone to systematic errors as long as the properties of the sources are not fully understood. Ongoing experiments at the Sanford Underground Research Facility with the goal to characterize seismic fields in three dimensions are expected to deliver first data from an underground seismometer array in 2015 (see [89] for results from an initial stage of the experiment). While most people would argue that constructing GW detectors underground is always advantageous, it is still necessary to estimate how much is gained and whether the science case strongly profits from it.…”