Using SAR (synthetic aperture radar) interferometry, earth movements can be detected retrospectively.
This technology is based on the evaluation of the phase difference of microwaves reflected from the Earth's surface. On the one hand, two images of the same area can be used to create very accurate elevation models, regardless of weather conditions and time of day. On the other hand, multitemporal data can be used to determine subcentimeter-scale terrain displacements without resorting to complex and expensive terrestrial surveying.
In SAR interferometry, observation of selected points is distinguished from observation over larger surface areas. The point-observation method used here (Persistent Scatterer) is particularly suited for urban areas. Natural reflectors allow for a millimeter-scale analysis of object movements.