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[SCG52-P10] Inversion method to determine multiple stress tensors and friction coefficients using fault-slip data
Keywords:fault-slip analysis, stress tensor inversion, friction coefficient, fault instability
In order to estimate the crustal stress states, stress tensor inversion techniques using geological fault-slip data and seismic focal mechanisms are widely used. Most of such techniques assume that a fault slips along the shear stress on the fault planes (Wallace-Bott hypothesis) and minimize the misfit angle between observed slip directions and calculated shear stress directions. Meanwhile, the orientation of a fault is expected to carry information on friction coefficient as is expressed by a simple model of conjugate fault system. By maximizing the fault instability [1], which is a measure of tendency of fault to slip, a representative value of friction coefficient can be calculated by analyzing the orientation distribution of a population of faults [2].
This study tried to combine the above-mentioned techniques to simultaneously determine the stress condition and the friction coefficient by analyzing a set of fault-slip data. The new method attempts to minimize the misfit angles and to maximize the fault instabilities. A graphical expression of result enables us to distinguish multiple conditions of stress and friction.
Some artificial fault-slip data were analyzed to assess the performance of the present method. As the result, the following two advantages were found. Firstly, the present method enhances the detectability of stresses when fault planes are concentrated in the orientations of high fault instability. Secondly, the method is moderately robust to the change in stress state after formation of fault planes.
The new method was applied to natural outcrop-scale faults in the Pleistocene Sekinan Group distributed along the Beppu-Shimabara graben, southwest Japan. A N-S trending tensional stress with the friction coefficient of ~1.0 and a ENE-WSW trending tensional stress with the friction coefficient of ~0.6 were detected. Since only the former stress was also detected from the overlying Oita Group, a change of stress and friction conditions at ~0.9 Ma was inferred.
References
[1] Vavrycuk, V., Bouchaala, F. and Fischer, T., 2013, Tectonophysics, 590, 189-195.
[2] Sato, K., 2016, Journal of Structural Geology, 89, 44-53.
This study tried to combine the above-mentioned techniques to simultaneously determine the stress condition and the friction coefficient by analyzing a set of fault-slip data. The new method attempts to minimize the misfit angles and to maximize the fault instabilities. A graphical expression of result enables us to distinguish multiple conditions of stress and friction.
Some artificial fault-slip data were analyzed to assess the performance of the present method. As the result, the following two advantages were found. Firstly, the present method enhances the detectability of stresses when fault planes are concentrated in the orientations of high fault instability. Secondly, the method is moderately robust to the change in stress state after formation of fault planes.
The new method was applied to natural outcrop-scale faults in the Pleistocene Sekinan Group distributed along the Beppu-Shimabara graben, southwest Japan. A N-S trending tensional stress with the friction coefficient of ~1.0 and a ENE-WSW trending tensional stress with the friction coefficient of ~0.6 were detected. Since only the former stress was also detected from the overlying Oita Group, a change of stress and friction conditions at ~0.9 Ma was inferred.
References
[1] Vavrycuk, V., Bouchaala, F. and Fischer, T., 2013, Tectonophysics, 590, 189-195.
[2] Sato, K., 2016, Journal of Structural Geology, 89, 44-53.