Electromagnetic radiation (EMR) and its interpretation in terms of stresses in the lithosphere

Electromagnetic radiation (EMR) as measured at the surface of the lithosphere or underground shows preferred orientations, which can be related to microcracks and other brittle structures at micro and nano scales (see Bahat et al. 2005 and references therein). During the last years, numerous studies showed the applicability of EMR measurements for the determination of active fractures and stress orientations. EMR is determined with a ‘Cerescope’, which picks up EMR signals at frequencies from 5– 50 kHz (Obermeyer, 2005) with a ferrite aerial and processes them electronically so that the results can be displayed on a screen or copied to a computer. With the help of oriented EMR measurements, intensity variations are determined, which can be related to preferred crack fracture orientations. From this information, orientations of the principal stresses can be calculated. In addition, the intensity of the EMR is related to stress magnitudes...