Pattern of normal faulting in the Gediz Graben, SW Turkey

Abstract

Hanging-wall deformation of the fault systems controlling the southern margin of the Gediz Graben were investigated separately within the Plio-Quaternary and Neogene (predominantly Miocene) deposits of the graben fill. Fault styles observed in both packages share many similarities in terms of geometry and comprise conjugate fault sets that show clustering of strike orientations predominantly around WNW–ESE but also SW–NE and NW–SE directions. The main difference between the two units is observable in terms of fault dips and rake of the slickenside lineations measured on the exposed fault planes. Both measurements show a uni-modal distribution for the Plio-Quaternary deposits but a tri-modal distribution for the Neogene deposits. This variation is probably related to the geometrical modification of the older faults by the process of domino style back-rotation in the hanging wall of higher order faults. Similarities among the two units are not limited to geometrical aspects of the fault systems but also counts for the orientation of the principal stress axes that controlled the deformation during the deposition of each sedimentary package. Inversion of the fault-slip data showed that approximately N–S-oriented extension, which varies in the range of NNW–SSE and NNE–SSW, controlled the faulting during the accumulation of the entire graben fill, with almost no evidence of change in the state of stress during the graben evolution. However, some heterogeneity, in terms of stress field, is observable among the fault systems formed within the same time frame. This heterogeneity is probably related to poorly defined direction of extension in the graben. Indeed, low ϕ-ratio in the order of 0.25 suggests that ( σ 2) and ( σ 3) are close in magnitudes and the direction of extension is not well-constraint with a potential of ( σ 2)/( σ 3) axes permutations. Local stress field anomalies related to fault segment interaction could also contribute to the observed heterogeneity.