[SIT26-P02] Stress tensor inversion for heterogeneous fault-slip data using fault instability evaluation
Keywords:stress tensor inversion, fault-slip analysis, fault instability
The fault instability of a fault is defined as the nearness of the point representing shear and normal stresses on Mohr diagram to the friction envelope tangent to the Mohr's stress circle. The calculation of fault instability requires the friction coefficient. The new method tries to find the optimal stresses on the basis of grid search. For each candidate of stress solution, the optimal friction coefficient is estimated by the method of Sato (2016) which maximize the fault instability. Then, the weights propotional to the sums of fault instabilities are imposed on the candidates. Finally, the optimal stresses should have larger fault instabilities according to the observed orientation distribution of fault planes.
The new method was applied to meso-scale fault-slip data gathered from the Pleistocene Sekinan Group, Beppu area, southwest Japan. Three normal-faulting stress tensors were detected with NNE-SSW, NNW-SSE and E-W horizontal tension axes. Compared with the conventional stress tensor inversion method (Sato, 2006) which could detect two tensors at most, it was confirmed that the detectability of stresses were enhanced with the evaluation of fault instability.
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