مجله زمین ساخت
پیاپی 16 (زمستان 1399)

The Sefid-Zakhur anticline is located in an area of Fars province where the gas potential on the Dehram horizon is high. The restored sections have been studied in three western, eastern and central parts of this anticline, deformation in this area is caused by a combination of compressive and shear deformation and tilting of layers in the end sections in the non-deformation stage, it indicates the existence of shear plates (separation horizons) between the stratigraphic units. Based on the order of formation of faults on sections, it can be concluded that first progressive thrusts and then as the deformation progresses, back thrusts are formed. The deformation in this region is related to the beginning of the Zagros deformation in Miocene time and is not older than that. According to the growth strata observed in the carbonate member of Gachsaran Formation in Sefid-Zakhur anticline, compression and folding in this area occurred during the Early Miocene. The southwestern part began to form earlier and formed as detachment fold with box geometry above the lower detachment horizon. In the higher deformations, the deformation occurs to the northeast, and the anticline forms detachment fold with a chevron geometry. The geometry of fold in the eastern part is a box fold. The degree of deformation in the eastern part is less than the central and west parts. Generally, Sefid-Zakhor field and its surrounding fields are formed based on the action and reaction of the compressive force of the region and the separation horizon.

In this research, seismotectonic analysis has been done Guriyeh area (subsidiary of Shooshtar city, Khuzestan province, Iran) with radius of 25Km. In this research, nine months of Guriyeh earthquake swarm from 2017-11-15 to 2018-7-20 has been studied. The main purpose of this study is to provied evidences to prove the activity of new seismic trends and finally, the need to strengthen historic and dilapidated buildings in this area. Seismogenic history, field evidences, epicenter locations (in the form of seismic bunch) and their migration trend toward Southwest (N30E), indicate the activity of Northeast-Southwest seismic trend in the vicinity of Northwest-Southeast seismic trend (Zagros trend) and their conformity with location of surface and subsurface faults in this region. It also expresses the focal mechanism provided for earthquakes in this region, the compression mechanism and some cases with oblique right-slip component, for faults causing seismogenic in this area. The main collected evidence indicates reactivation of Sardarabad fault, subsurface fault(UGC-FAULT) and magnetic lineament (MGL-1). To continue, seismic hazard analysis has been done using deterministic approach for this region, and maximum seismogenic power (MSmax), 7.14 in Richter scale for the subsurface fault(UGC-FAULT) and peak ground horizontal acceleration(PGA)of 0.27g for the magnetic lineament (MGL-1) were calculated.

Landslide is a natural phenomenon that causes severe erosion of the earth's surface and may cause financial and human risks. The Havanan landslide has occurred in the mountains south of Birjand. The lithological, topographic and structural conditions of the area are such that, in the rainy season the conditions for reactivation of the landslide are provided. Due to the creeping movement of materials downwards, the old portion of the Havanan village is gradually being destroyed, and its fields are being damaged due to being located at the edge of the valley. In this paper, using geological, geoelectric, seismic and area mapping studies, the surface and subsurface conditions of the earth have been studied. According to local evidence, the Havanan landslide is a large transitional landslide. Although the main motion is a plane slip, the presence of several flat areas in the region indicates the occurrence of local rotational slides. The geoelectric study showed that the sliding mass thickness is between 10 to 30 meters, and the base rock is a sound ultramafic. According to the two stages of on-site mapping, the sliding mass moves an average of 23 mm per year. Also, the appearance of new cracks in the walls of houses, and the sounds heard occasionally, indicate the slow creep movement of the sliding mass.

Considering that the relationship between active tectonics and geomorphology has not been studied in the study area so far; It seems necessary to study the tectonic morphological characteristics in order to identify the impact of active tectonics on the area. In order to study the active tectonics in the study area, the morphometric indices of the catchment such as integral index and meta-measurement curves, catchment asymmetry index, transverse topographic asymmetry index, waterway slope index, mountain front maze index and The elongation ratio is used. In order to establish the relationship between structural elements such as lines, faults and morphometric indices, remote sensing studies such as automatic extraction of lines and fractures and density map of lines have been performed. The study of the risk of surface rupture in Pardis shows that the bed of this city hosts important faults that in the initial studies of this city, geological conditions and construction studies have not been considered. According to the results of the study of relatively active tectonics in the study area, it can be concluded that most of the total area under study is in the category of high tectonic activity due to the performance of faults in the area. Comparison of the density map of the ridges with morphometric indices indicates that the high density areas correspond to the active fronts and the density map of the ridges is a confirmation of the high tectonic activity in these areas.

Miamei city is located in the east of Semnan province and It is important to seismic study because of proximity to the active Miamei Fault and recorded seismic events. Miamei, Hokmabad and Armian Faults are more importance for Seismic sources around Miamei city. In this research two methods (Gutenberg-Richter and Kijko-Selevoll methods) have been used for seismic statistical studies. Statistic studies based on Gutenberg-Richter show a 100 years return period for an earthquake with magnitude 6.5 Richter. Also based on Kijko-Selevoll show a 100 years return period for an earthquake with magnitude 5.9 Richter tat statistically has more coincide with actual events. The results of probabilistic seismic hazard analysis around the Miamei city at a radios 150 km indicate maximum horizontal acceleration of 0.7g in a 475 years return period. In this zoning, Miamei city is located in horizontal acceleration of 0.3g-0.4g which can be considered as a city with high seismic hazard class in area.

The Zagros fold-thrust belt is one of the most seismicity active zones of the Iranian plateau and Its seismic behavior has certain complexities and changes in space and time under influence of various factors. Based on various studies on seismic data recorded in the area between Kazerun and Sarvestan faults, Some complexities in the seismicity changes of this part of the Zagros fold and thrust belt have been investigated. The main faults in the region are Zagros Mountain front faults, Zagros foredeep fault, Kazerun-Borazjan, Sabzpooshan, Qir and Sarvestan Faults. By preparing scattering maps and depth changes of seismic data, it was determined that earthquakes are mainly concentrated around the main faults in terms of number and magnitude and occurred at depth of less than 20 km.. Estimation of seismic parameter by using Gutenberg-Richter model shows the β value is 1.55± 0.03 and λ for Mmin equal 2.8 is 12.07±0.6 . Spatial changes of seismicity have been investigated using networking and plotting changes of a-value and b-value parameters. Changes in a range from 3.98 to7.64.The changes of b in the region are from 0.44 to 2.4. The highest value of a and b occurred in the western and southeastern part of the region Which indicates the existence of smaller earthquakes that occurred in these parts and more of them. Analysis of seismic data shows that one of the seismic factors of the region is transverse faults that are mainly basement faults and control the shape of the folds in the area.