Effects of Ground Motions on Amplitude Interferometry

Abstract

AbstractSome examples are given of types of ground motion which hs.ve been observed with seismic and geodetic instruments. In general, away from sources of man-made noise, the amplitudes of ground strains and tilts in the microseism band with periods of a few seconds normally are of the order of a few times 10-10. Strain and tilt tides give amplitudes of a few times 10-8, and long term average strain and tilt rates at relatively good sites may be roughly 10-7/yr. Superposed on such relatively long wavelength motions can be larger local pier motions, which are likely to be irregular. However, very high ground stability has been demonstrated at a few sites The limitations of ground motions on long term amplitude interferometer stability are serious if applications such as earth rotation and polar motion measurements are considered, but at shorter periods the environmental problems will be almost completely atmospheric.