The magnitude of the rms motion of the interferometer test masses, , can be shown to be 
However, there are two proposed approaches for reducing the level of gravity-gradient noise in future ground-based detectors. A monitor and subtraction method can be used, where an array of seismometers can be distributed strategically around each test mass to monitor the relevant ground motion (and ground compression) that would be expected to couple through local gravity. A subtraction signal may be developed from knowing how the observed density fluctuations couple to the motion of each test mass, and can potentially allow a significant reduction in gravity-gradient noise.
Another approach is to choose a very quiet location, or better still, to also go underground, as is already going ahead for LCGT . Since the dominant source of gravity-gradient noise is expected to arise from surface waves on the Earth, the observed gravity-gradient noise will decrease with depth into the Earth. Current estimates suggest that gravity-gradient noise can be suppressed down to around 1 Hz by careful site selection and going 150 m underground . The most promising approach (or likely only approach) to detecting gravitational waves whose frequency is below 1 Hz is to build an interferometer in space.
Living Rev. Relativity 14, (2011), 5
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