MiningInduced Stress Transfer and Its Relation to

Authors: Moritz Ziegler Karsten Reiter Oliver Heidbach Arno Zang Grzegorz Kwiatek Dietrich Stromeyer Torsten Dahm Georg Dresen Gerhard Hofmann

Publish Date: 2015/02/01

Volume: 172, Issue: 10, Pages: 2557-2570

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Abstract

On 27 December 2007 a textM w 19 seismic event occurred within a dyke in the deeplevel Mponeng Gold Mine South Africa From the seismological network of the mine and the one from the Japanese–German Underground Acoustic Emission Research in South Africa JAGUARS group the hypocentral depth 3509 m focal mechanism and aftershock location were estimated Since no mining activity took place in the days before the event dynamic triggering due to blasting can be ruled out as the cause To investigate the hypothesis that stress transfer due to excavation of the gold reef induced the event we set up a smallscale 450times 300times 310textm3 highresolution threedimensional 3D geomechanical numerical model The model consisted of the four different rock units present in the mine quartzite footwall hard lava hanging wall conglomerate gold reef and diorite dykes The numerical solution was computed using a finiteelement method with a discretised mesh of approximately 106 elements The initial stress state of the model is in agreement with in situ data from a neighbouring mine and the stepwise excavation was simulated by mass removal from the gold reef The resulting 3D stress tensor and its changes due to mining were analysed based on the Coulomb failure stress changes on the fault plane of the event The results show that the seismic event was induced regardless of how the Coulomb failure stress changes were calculated and of the uncertainties in the fault plane solution We also used the model to assess the seismic hazard due to the excavation towards the dyke The resulting curve of stress changes shows a significant increase in the last sim50textm in front of the dyke indicating that small changes in the mining progress towards the dyke have a substantial impact on the stress transferThe authors would like to thank AngloGold Ashanti for kind permission to work with and publish data on the Mponeng Gold Mine and the JAGUARS group for provision of data The authors would like to thank two anonymous reviewers whose comments and suggestions helped to improve the manuscript Furthermore the authors would like to thank Lanru Jing for his comments on an earlier version of the manuscript Figures 1 2 3 and 7 were generated with the Generic Mapping Tool GMT Wessel et al 2013 In Fig 1 SRTM3 V2 topographic data were used The beachball plot in Fig 2 was realised with the software MoPaD http//wwwmopadorg by Krieger and Heimann 2012 Previously published preliminary results presented in a conference proceeding Ziegler et al 2014 contain some erroneous results and misinterpretations and should no longer be used

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