مجله زمین ساخت
پیاپی 11 (پاییز 1398)

The Amiran anticline with about 50 km length is located in NW-SE of the Zagros fold and thrust belt and the Lurestan sub-zone. The aim of this study was to investigate the role of thrust and basement strike-slip faults on the structural geometry of this anticline. For this purpose, three cross-section perpendicular to the anticline axis have been constructed in the NW, central, and SE parts of the anticline. A basement thrust fault in the southwestern limb of this anticline and two upper (Amiran Formation) and Middle (Garau Formation) detachment levels affect the folding geometry and led to the formation of disharmonic folding. In addition to the thrust fault at the southern limb, an N-S basement strike-slip fault in the middle part of the anticline has shifted the anticline axis from N50W in the southeast to N65W in the northwest. The disharmony of fold axis across the surface and deep structures and migration of the southern limb of the anticline is due to the effect of the basement structures on structural geometry of the study area. Therefore, basement strike-slip faults propagate to the inner parts of the fold-thrust belt in the Lurestan sub-zone and cause deformation of surface and deep anticlines.

Abstract The study area to the west of Lake Urmia includes the city of Urmia and surrounding region. In this study, Ez-Frisk and kijko software have been used to the probabilistic seismic hazard analysis (PSHA) of this area. The return period of earthquakes and seismic coefficients of the region was calculated by Gutenberg-Richter method by Zmap software. The results of this study show that the probability of earthquakes with magnitudes above 6 Richter is about 10% in the next 100 years. The high level of b-value seismic parameter indicates the frequency of low magnitude earthquakes and high seismic rates in the region.The results of probabilistic earthquake hazard analysis by Ez-Frisk software for linear and seismic sources around the city of Urmia at a radius of 100 km indicate 0.4 g bedrock acceleration in the 475 year return period. The earthquake risk map in Urmia also shows the highest acceleration in the southwest and the lowest acceleration in the east of the Urmia city.

Some researchers calculate the vertical movement of earth surfaces by using Triple methods Morpho-Tectonics indexes, GPS measurements & Numerical Modeling and Inter-ferrometric SAR. In using of these methods, the viewpoints are formed on the basis of Morphometric or local scale vertical movements and don’t any attention to movement causalities. In this research, the vertical movement of Western Kopet Dagh are calculated by using D-InSAR (used 2004-2010 Radar Image), Then, the surface & subsurface structure are extracted and determined by Remote Sensing Techniques, field surveys and subsurface data. In follow, the relationship between structures and vertical movement are determined by using of functions in GIS environment. The results shown that the uplifting taken placed in partition between Sariqamish and Kalaleh Faults in Southern areas of Northeastern subpart. Whereas, the uplifting occurred in Northern areas in all of the Western Kopet Dagh. Also, two abnormal uplifting shown in subsided Gorgan – Gonbad Kous Plain, due to growth of subsurface & surface folds. Therefore, it is defined that significant part of vertical movement Patterns related to main structures such as main faults and folds.

Determination of geometry of shear zones will help us to understand the structural evolution of shear zones. Determination of vorticity vector based on 3-D structural studies in many cases is very difficult. Study of lineations, foliations, shear zone boundaries and vorticity normal section are very important and will help us to understand the geometry of shear zones. In this research with application of theoretical aspect of shear zones the main parameters of shear zones geometry were studied. Moreover, for determination of shear sense indicators and deformation geometry a case study was carried out in the Kamery shear zone southwestern Hamedan whitin the Sanandaj-Sirjan metamorphic belt. Our results show occurrence of an important dextral shear component and scattering of lineation and pole of foliation around vorticity normal sectionDeformation temperature analysis based on opening angle of quartz c-axis pattern reveals the deformation temperature between 550±50 to 640±50 °C. Finally, the Triclinic Inclined Transpression model was suggested for structural evolution of this shear zone.

The Mahneshan sedimentary basin is one of the Cenozoic syntectonic basins in the Central Iran, which is located between the western Alborz Mountains and the Takab Complex. Our study area at the Mahneshan mainly includes Kahar Formation and granitic, gneissic and metamorphic units of the Takab complex and Cenozoic sedimentary and volcanic sequences including the Upper Red, Qom and Lower Red Formations. In this study, by combination of remote-sensing and extensive field mapping including fault kinematics, fold geometries, growth strata patterns and unconformities, a structural cross-section constructed across the Mahshan Basin and the Takab complex and geometric and kinematic relationships of the geological units were determined. According to the cross-section, the NW-trending Mahneshan fault zone show an almost pure reverse mechanism with a right-lateral strike-slip component. On the other hand, the NW-SE trending faults of Takab complex have right strike-slip mechanism. Fault systems with thrust and strike-slip kinematics have aligned almost parallel in the Mahneshan Basin and Takab Metamorphic complex that documents prominent strain partitioning in a transpressional deformation regime during post-Oligocene time. This structural model confirms hypothesis on strain partitioning documented in other studies for the Central Iranian Basin. Syntectonic growth strata development in the Lower Red Formation and also sedimentary unconformities and onlap of the Lower Red and Qom Formations on older sedimentary and metamorphic units in the Takab complex and Mahnashan basin suggests that their deformation initiated during the latest Oligocene, which can be attributed to the onset of Arabia–Eurasia collision and exhumation of the western Alborz Mountains.

Seismic analysis of earth and rockfill dams is generally done in two ways: quasi-static and dynamic. However, a quasi-static method with easy application and simple assumptions may lead to unsafe and uneconomical results. In the present study, two static and dynamic analyzes have been used nonlinearly using the Rayleigh Damping rule to calculate the stress and strain of Azadi Dam in the stages of the end of construction and steady-state seepage. Also, in numerical analysis, Abaqus software and simple elastoplastic behavior model based on the Mohr-Coulomb criterion have been used. The results show that in both quasi-static and dynamic seismic analysis, the highest strain of the Azadi Dam core occurred at the upper levels of the core and the highest stress occurred at the level of the core floor. The stress in the dynamic state is higher than the quasi-static one in the directions σxx 49%, σxy 30%, and σyy 28%. Also, the maximum crust stress on the floor, middle and upper levels is 29%, 68%, and 72% higher than the core, respectively.