Measurements and interpretations of tilt–strain gauges in seismically active areas

An overview of different aspects of deformation measurements is given. An introduction to the general theory of point-crustal deformations with an application to the stress–strain relations at the earth surface is made. The instrumentation used in crustal deformation measurements is briefly explained, emphasizing different constructions of tilt and strainmeters. The problems connected with the housing of the instruments, i.e., the cavity and topography effects, and with the ambient noise factors, as the hydrological and pressure effects, are discussed. The last part of the paper is concerned with the relation between deformation measurements and seismic events, both from a theoretical and observational standpoint. A number of examples are shown that report on pre-, co-, and post-seismic and the secular term deformation in different areas of the world.