In late 2015, the LIGO project team announced the detection of gravitational waves. The detector is (very basically) a laser measuring the distance between two mirrors in vacuum, over a large-enough distance to detect very small changes.
The two mirrors are installed on Earth, and a couple kilometers apart.
I believe, perhaps mistakenly, that tectonic activities (if only vibrations) may change the mirror distance over time, so the LIGO project has probably used some model and technology to nullify their effects.
How can that be done? If there is any mistake there, I wonder about how to validate the experiment results.