INVESTIGATION OF FRACTURE PROCESSES USING MOMENT TENSOR INVERSION TECHNIQUE

The development and progress of fractures is accompanied by the radiation of acoustic waves due to microcracking. In the transient waveforms of acoustic emissions a huge number of infor-mation about fracture processes and the state of the material is inherent. Signal-based analysis of acoustic emissions allows, amongst other studies, for a fracture-mechanics based investigation of failure. From the spatial distribution of seismic energy, an inversion on a system of equivalent forces – the so-called seismic moment tensor – is performed. The inversion is simplified by the assumption of a point source and the omission of near-field effects, implying that the source vol-ume is small compared to the distance between source and receiver. With the help of the moment tensor, arbitrary and complex source mechanisms can be described. For an interpretation of the results, the moment tensor is decomposed into simple fracture modes on the basis of an eigen-value analysis. Furthermore, the appropriate radiation pattern of particle motion of the moment tensor is plotted on a sphere enclosing the source, revealing a 3D-visualization of the stress field. These results and additional data from further investigations can be combined in a comprehen-sive representation of the failure. Basic principles of moment tensor inversion and some exam-ples of experimental data and their analysis are presented