ABSTRACT
A technique for accurate measurement of time-dependent changes in seismic propagation velocities are presented The focus of this technique is to monitor changes in elastic stresses acting on the subsurface down to a depth of several kilometers. In addition, motion of fluids can also be detected by this technique. The method utilizes elastic waves, which are generated continuously by large imperfectly balanced machines running synchronously with the power network. We make use of the solid Earth tides as test signals, since they are associated with known stresses in the Earth’s interior. That test signal suggests that we are indeed observing effects related to changes within the Earth. In that sense, the method should be superior to surface deformation measurements, in which the changes at depth are frequently masked by near-surface artefacts
