علی سربی

The sensitivity of the drainage pattern to the active tectonics processes leads to a geomorphic expression that provides a useful tool to evaluate relative tectonic activity (Cox, 1994). Geomorphic indices provide a useful method for assessing the extent of tectonic activity; Especially in areas where earthquakes happen on faults in which there was not enough information in advance. The study area is in the west of Lut block, southeast of Iran, which is in the range of longitude from 55°22ˊ 15˝ to 58° 31ˊ17˝E and latitude from 28°50ˊ4˝ to 31°9ˊ30˝N. This region has a long history of devastating earthquakes, the historical types of which date back to around 1850AD. The occurrence of earthquakes on previously unknown faults (Bam, 2003) and the need to pay attention to areas in this part that have not yet experienced a devastating earthquake despite being surrounded by active faults (Kermen city), are the most important reasons that led us to find the best way of morphotectonic analysis and compare the results to seismic structures and data as a tool to identify structures and their activities also to estimate the seismic risk.

To obtain the drainage network layer, basins area, and water dividing layer in the study area, the hydrological modeling process was done by Arc GIS10.3 software. The basic data used are 30 m resolution DEM and geological maps. Also, to investigate the relationship between seismicity and tectonic activity, seismic data were used for earthquakes greater than 0.4 Mw. In this study, the results of calculating 7 geomorphic indices, including stream length-gradient index(SL), drainage basin asymmetry(Af), hypsometric integral(Hi), the ratio of valley-floor width to valley height(Vf), index of drainage basin shape(Bs), index of mountain front sinuosity(Smf), and Transverse Topographic Symmetry Factor(T), for 51 basins were analyzed by Iat and AHP methods. Finally, by using seismic data and field studies, we discuss our findings to compare the accuracy of AHP and Iat methods in analyzing morphometric indices to assess seismic risk, which is the aim of this paper.

The evaluation of the distribution of relative tectonic activity in the study area according to Iat, which is obtained by averaging the different classes of morphotectonic indices, divided the region into three categories in terms of tectonic activity. Class2, class3 and class4, have allocated 5.9%, 54.9%, and 39.2% of the total study area to themselves, respectively. It should be noted that none of the basins were in class1. 43.2% of epicenters were located in basins with high activity and 17.6% in low ones. Since the Iat index is not based on the weighting of the indices, all the indices were calculated with equal importance ratios. Therefore, there are some inconsistencies in comparing the Iat distribution map with the main structures of the region and the epicenter of the earthquakes. The AHP makes it possible to determine the amount of tectonic activity in the study area base on the weight and importance of each index compared to others, instead of relying solely on the average of each index (Iat). The values of the coefficient of determination(R2) are extracted from the graph of the indicators relative to each other. The correlation coefficient(R) was calculated from the roots of R2. After checking the acceptability of the Inconsistency, the final weights assigned to each of the indicators are (0.015)Bs, (0.012)Smf, (0.025)AF, (0.021)T, (0.104)Hi, (0.116)Vf, (0.708)SL. These results were classified into four categories. Accordingly, class1, class2, class3 and class4, occupy 21%, 24%, 31%, 24% of the total study area, in turn. The basins with very high and high tectonic activity, are all located along the main faults of the region, in addition, the distribution of earthquakes in these basins (81.8.% of earthquakes were in high active basins and 4.4% in low ones), shows how they are consistent with the results of AHP.

In this study, we tried to more accurately assess the impact of active tectonics and determine the most appropriate method for analyzing geomorphic indices, by comparing the results obtained from Iat and AHP methods. Proper matching of geomorphic features, calculated indices, and classification of relative tectonic activity obtained by the AHP, with the main structures, field observations, seismic data and previous studies in the study area, confirms the significant superiority and higher accuracy of AHP over the Iat in the identification of tectonically active areas which subsequently leads us to seismic hazard assessment. Based on the final map derived from the AHP, the study area was divided into four tectonic activity classes. The results show that morphological features in the study area are strongly affected by the main faults. The basins along them, generally show very high to high tectonic activity rates. The existence of many active faults, the epicenter of earthquakes and the location of most cities in the study area within or adjacent to basins with very high to moderate tectonic activity indicate the need for attention and additional studies there.The findings of this paper show how using a suitable way of morphometric analysis can help us to identify areas with the potential for seismic hazards. Due to its low-cost and timesaving, this method can be a good alternative for expensive and complex methods, especially in vast and remote places. As a result, it can be a useful tool for regional planners and decision-makers involved in seismic risk assessment and disaster risk reduction.

The Sarvak and Ilam Formations in the Zagros sedimentary basin are known as hydrocarbon reservoir formations. More than half of the hydrocarbon fields in the Zagros Basin on the Sarvak and Ilam horizons contain hydrocarbons. In this research, to identify areas with hydrocarbon potential of the horizon of Sarvak and Ilam at Bandar Abbas hinterland, parameters such as outcrops of formations, main faults, salt plugs, isopach maps and upper sediment volume of formations from the geological map of the region and well data were extracted. With designing a network inference among data and using Fuzzy logic method with the high hydrocarbons, potential of the Sarvak and Ilam horizons were identified in the Bandar Abass hinterland. This area identified as a relatively weak area in terms of exploratory potential in Sarvak and Ilam reservoir horizons. 68% of the hinterland region has low hydrocarbon potential, 18% has medium hydrocarbon potential and only 14% has high hydrocarbon potential for exploration in Sarvak and Ilam horizons. However, considering the effect of anticlines, the mentioned percentages for areas with high hydrocarbon potential reduced to 4.3%. Together, it seems that the anticlines of South Gashu, Bastaneh, Kisn, West Namak and Suru have hydrocarbon potential in Sarvak and Ilam horizons.

In the Northern part of Suture Zone (Kermanshah) the deep sea sediments, oceanic crust remnants, platform carbonates, igneous and metamorphosed rock of active margin and carbonate sequence of passive margin are assembled in this studied area. This convergent area has provided a very complicated structural zone. The main purpose of this study is stress characteristic analysis. A great data has gathered from the faults which are appeared within the rocks specially the radiolaritic rocks. The data includes characteristics of fault surface geometry, fault slip and lineation slip related. By using the method Right Dihedral, the position of main stress was obtained. The great number of reverse faults have a NW- SW trend, while the strike- slip faults, show a NE- SW direction. The Normal faults with a different displacements appeared younger than the other faults. The result of this study that we obtained the situation of main stress σ1, σ2 and σ3 respectively is 059, 305 and 195.

Geomorphic indices of active tectonics are useful tools to analyze of the active tectonics in a large area. These indices have the advantage of being calculate from the software and remote sensing packages over large area as a reconnaissance tool to identify geomorphic anomalies possibly related to active tectonics. This is particulary valuable in Ajichai basins where relatively little work on active tectonics based on this method was done, so this method is new and useful. Based upon valuable of the stream length-gradient index(SL), drainage basins asymmetry(Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), drainage basins index shape (Bs), and index of mauntain front sinuosity (Smf), we used an overall index (Iat), that is a combination of the other indices that divides the landscape into four classes of relative tectonic activity. The moderate class of Iat is mainly in the class 2 (high), with 1045.46 Km2 ,11.26 percent, class 3 (moderate), with 2940.67 Km2 ,31.67 percent and with 5297.30 Km2 ,57.06 percent occupying of all zone. The stream network asymmetry (T) was also studied using morphometric measures of Transverse Topographic Symmetry. Analysis of the drainage basins and sub-basins in the study area results in a field of T-vectors that defines anomalous zone of the basins asymmetry. A comparison of T index clearly consist with the values and classes of active tectonics indices and the overall Iat index.

Mass movements, especially landslides, are one of the natural hazards that to a large extent occur, are controlled, or are prevented by human. It is obvious that human interferences in nature regardless of stability conditions and its natural balance leads to physical reactions from the environment to return the sustainability and balance. Damages caused by the landslides, which have been growing in recent decades, have made humans to find appropriate solutions to reduce and control this phenomenon. Zonation of areas susceptible to landslide is one of the most widely used methods to avoid hazardous areas or applying controlling methods in hazardous areas. This research uses artificial neural network for zonation of landslide susceptibility in the Qazvin-Rasht quadrangle area. The studied area is one of the most susceptible areas for landslide event in terms of topography, climate, and geology, as the history of the area shows 338 recorded landslides. Fifteen variables studied in other researches as effective variables in occurrence of landslides were selected to investigate this area. By combining these variables and the map of existing landslides, value of each of the 15 variables was extracted for sliding points. In the next stage, a number of points (1000 points) were randomly selected from the area and values of these variables were extracted for them. Each of the two data sets was divided into two training (70%) and test (30%) categories. We combined each of the two training and test categories, and used their output for training and testing the network. The number of internal layers of the neural network was determined to be 9 layers based on trial and error method and calculation of the root mean square error value (RMSE = 0.4041). The constructed neural network is of feedforward networks type with back-propagation algorithm and its training algorithm is of Levenberg-Marquardt back-propagation training algorithm type. After training and testing the network and conducting necessary corrections on it, the constructed neural network was used to predict the sensitivity of landslides in studied area. We placed results of this prediction in a range from 0 to 1 and obtain the best zonation map of the landslide susceptibility by choosing a threshold. Final evaluation of the zonation map of landslide susceptibility in the Qazvin-Rasht quadrangle shows an error of approximately RMSE = 0.4164 and the constructed neural network identifies 298 out of 338 occurred landslides in the high-risk zone, indicating the accuracy of 88.1%.

In terms of natural fractures, Iranian carbonate reservoirs have a global reputation. These fractures are known as dramatically important factor in the exploration and production of hydrocarbons. Many important oil and gas fields are classified based on the production from fractured reservoirs. At the first step, the aim of this study is the investigating the structural evolution of Farour B gas field and then determining how the detected fault influences this gas field. For this study, 2D seismic data, Persian Carpet-2000 (PC-2000), and all related information on the wells of the studied field were collected. Then these data were loaded on Petrel software,. Shifting and interpretation of all the chosen seismic lines were selected according to the excavation information from three wells and finally the deep balanced maps of formations and 3D patterns were provided. The flatting process was done for some seismic sections. According to seismic sections and tectonic analyzing the Farour B structure has two normal faulting trends in which the faults slope are approximately vertical and the eastern and western faults displacement are about 70 meter and 20 meter respectively.

Geomorphic indices of active tectonics are useful tools to analyze the influence of active tectonics. These indices have the advantage of being calculated ArcGIS and Remote Sensing software packages over large areas as a reconnaissance tool to identify possible geomorphic anomalies related to active tectonics. This method is particularly new and useful in areas relatively little work has been carried out on active tectonics based on this method. Based upon the values of stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf), we used an integrated index (Iat) that is a combination of the other indices. This index divides the landscape into four classes of relative tectonic activity. According to the Iat results, sub-basins 4 and 6 show zones of low tectonics activity (Class 4), sub-basins 1, 2, 7, 9, 10, 11, 12, 14, 15 and 19 fit to areas of moderate tectonic activity (Class 3), and high tectonic activity is represented by sub-basins 3, 5, 8, 13, 16, 17 and 18 (Class 2). The Tranverse Topographic Symmetry (T) was also studied using morphometric measurements, which finally gave a plot of T-vectors defining anomalous zones of basin asymmetry. A comparison between T index and map of relative tectonic activity showed a consistent coincidence between areas of higher Iat classes with zones of greater asymmetry.

In this paper, the relative active tectonics of the Mordaq-Chai basin has been discussed according to the geomorphic indices using Global Mapper software. The calculated indices are as follows: stream length–gradient index (SL), hypsometric integral (Hi), ratio of valley floor width to valley height (Vf), index of drainage basin shape (Bs),index of mountain frontsinuosity (Smf), asymmetry factor (AF), and transverse index of basin topographic symmetry (T). Using above indices results, led to calculation of relative tectonic activity index (Iat).The results show that the Mordaq-Chai basin’s relative tectonic activity index falls into two groups: the first one includes the areas around the Sahand volcano crater (upper part of sub-basin one) and the Goshayesh Valley (upper part of sub basin three), both of which have high levels of relative tectonic activity. The second one includes high lands located at northern part of the Maragheh fault towards the Kordeh-Deh village (sub-basins one and two), the opening of the Mordaq-Chai river into the Malekan plain (from the Ekiz village to the Sheikh-o-eslam village in central of sub-basin 3) and the southern portion of the Sahand Volcano’s crest (central part of sub basin one), which all have moderate levels of relative tectonic activity.