Paleostrees analysis and Evaluation of Movement potential of Dochah Fault, Central Iran

Qom region is one the significant area insight of geological features in Central Iran. Several researches have studied about the Cenozoic strata in terms of sedimentology, Stratigraphy and paleontology but, few structural detail data are available from this area. The most important exposure of the rock unites at the west of the Qom city is related to the Eocene volcanics, Lower Red, Qom and Upper Red Formations. Major structures at this area are Kamar Kuh and Mil anticlines, Yazdan syncline, Dochah and Sefid Kuh faults. Dochah Fault with E-W trending and ~70° dipping to the northward placed at the northwest termination of Qom-Zefreh Fault as a recent sinistral strike slip fault. This fault with ~15 km length separate Mil anticline from Yazdan syncline and eliminates the southern limb of Dochah overturned anticline. In this study, we focused on the Dochah Fault damaged zone in order to paleostress analysis using geometric and kinematic characteristics of fault slip data, which is achieved from the deformed Qom and Upper Red Formations. For this purpose, 100 fault slip data with precise and accurate geometric and kinematic characteristics have been measured in the field and analyzed with software Dasiy and Rotax methods. In order to determine the sense of shearing of the faults, the criteria of Petit (1987) and Doblas (1998) have been used. While the trend of the major structures is east-west but, most of slip data is related the transverse oblique slip faults, because the Dochah Fault passes through the soft materials of Lower Red Formation and consequently it is not possible or too hard to find the slicken line. Meanwhile, our results indicate the magnitudes of the axes of the maximum and minimum principal stress (σ1, σ3) as 030/05 and 285/05, Geometric and kinetic structural analysis related to the dochah fault and according to the spatial arrangement of the main stress axes indicate the readiness of the left-hand section on the right-hand section, especially in the western parts of the region (Caspian) attributed. oblate shape of field stress ellipsoid shape (R~0.7). Based on the field stress ellipsoid shape and the rotation of the fault data regarding the Anderson's theory for the compressive stress regime, the stress transition trajectory map has been prepared. The arrangement of maximum stress trajectories is consistent with the general stress regime in the Iranian crust and is consistent with the activity of the Dochah Fault. Different criteria have been proposed to evaluate the activity of a fault in terms of seismicity. In experimental studies, there are various estimates for selection of the part of the fault that the movement rediscovers for each tectonic seismic zone. Here, the possibility of moving Dochah Fault has been estimated by the method of Lee et al. (1997). In this method, the angular relationship between maximum principal stress axis (σ1) and the pole of the fault plane considered in order to evaluate the Fault Movement Potential (FMP) based on equation “FMP=f (G, σ)”. The angle between maximum principal stress axis (σ1) and the pole of Dochah Fault (θ) is equal to ~40° and so FMP=0.33 based on equation FMP= (θ-30°) ⁄ (30°) if θ∈[30°,60°]. This value of FMP indicates the low seismic potential of Dochah fault for movement and creating earthquakes.