Dynamic modelling of induced seismicity

A technique is presented to simulate seismicity in brittle rock under stress using a distinct element numerical modelling code. Itasca Consulting Group's particle flow code is used to model rock deformation, damage and the resulting seismicity. With this code, rock is represented by thousands of individual particles bonded together at points of contact. Seismicity results when bonds break under high local stresses and stored strain energy is released as kinetic energy. A full 3D formulation that enables the calculation of seismic event locations, magnitudes and mechanisms (moment tensors) is presented. A simulation of an axial compression test on a granite core sample is used to test the modelling technique. The source parameters of the acoustic emissions produced by the model are considered realistic when compared with similar experiments conducted in the laboratory. The technique is then tested on a field-scale problem by applying the algorithms to the 2D mine-by tunnel excavation simulation (Potyondy and Cundall, Int. J. Rock Mech. Min. Sci., this issue). Seismicity produced by the model is compared to actual seismicity recorded in the field and it is shown that locations, magnitudes and mechanisms match reasonably well. The similarities between the modelled and recorded seismicity provide confidence that the model is behaving in a realistic way. It is then shown how the model could be used to examine the details of the mechanisms behind the recorded seismicity by direct observations of particle forces and motions at the seismic sources.

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