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DDC:
550 - Earth sciences
Abstract:
In recent years more and more data has become available about focal depth of intra-crustal earthquakes as well as structure and distribution of physical and geologic-petrological parameters as a function of depth. This allows us to study the causes for increased earthquake occurrence at certain depth intervals. Besides structural and material inhomogeneities this is mainly controlled by depth and temperature-dependent variations of rheological properties of crustal materials. Intra-crustal earthquakes occur in an intraplate environment almost exclusively in the depth-range 2km < h < 20km with a clear maximum of activity between some 5 to 15km. The petrophysical as well as possible geologic-petrological reasons are discussed. The brittle fracture behaviour of crustal material is strongly controlled by the v"SUB p"/v"SUB s"-ratio. In crustal regions with v"SUB p"/v"SUB s" = or > 1.8 there is obviously no seismic activity. -from Authors
