Japan Geoscience Union Meeting 2018

Presentation information

[EE] Poster

S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Tectonophysics

[S-IT26] Stress geomechanics integrations: Observations, Modelings and Implications (OMI)

Sun. May 20, 2018 1:45 PM - 3:15 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:HungYu Wu(Japan Agency for Marine-Earth Science and Technology), Weiren Lin(Graduate School of Engineering, Kyoto University), Yoshinori Sanada((国研)海洋研究開発機構, 共同), Chung-Han Chan(Earth Observatory of Singapore, Nanyang Technological University)

[SIT26-P02] Stress tensor inversion for heterogeneous fault-slip data using fault instability evaluation

*Katsushi Sato1 (1.Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University)

Keywords:stress tensor inversion, fault-slip analysis, fault instability

Stress tensor inversion techniques are based on the Wallace-Bott hypothesis, which assumes that faults slip along shear stress vectors on fault planes. This hypothesis is applicable to faults with high pore fluid pressure and low friction such as preexisting faults in rock masses, since the magnitudes of shear and normal stresses are not constrained. However, in exchange for the wide applicability, the looseness of the assumption sometimes causes low detectability of stresses. In order to improve the detectability, this study proposes to incorporate the estimation of fault instability (Vavrycuk et al, 2013; Sato, 2016) into the stress tensor inversion.

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.
Sato, K., 2006, Tectonophysics, 421, 319-330.
Sato, K., 2016, Journal of Structural Geology, 89, 44-53.
Vavrycuk, V., Bouchaala, F. and Fischer, T., 2013, Tectonophysics, 590, 189-195.