Mohammad Ali Sharifi; Abbas Bahroudi; Saleh Mafi
Abstract
Extended Abstract Introduction Attitude determination of the fault planes and slid movements occurring on these planes are among the topics of interest to geoscientists. Among the methods that have been introduced to determine the attitude of the fault planes so far, the use of geological tools for justifying ...
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Extended Abstract Introduction Attitude determination of the fault planes and slid movements occurring on these planes are among the topics of interest to geoscientists. Among the methods that have been introduced to determine the attitude of the fault planes so far, the use of geological tools for justifying the geometry of the faults with surface outcrops, and examining the changes of the stress field and the displacements appeared on the Earth’s surface can be mentioned. The slip rate is calculated using the displacement of the sedimentary rock layers relative to the displacement time and the simulation models. Materials & Methods In this research, a geometric method is presented to calculate the slip rate of Zagros faults. We consider each fault as a continuous set of fault fragments whose surface positions are known. Given that most of the Zagros faults are hidden, locating thefaults is carried out using the geologicalmap of Iran’s faults. The first issue in performing these calculationsisto determine the attitude of the fault planes in the Zagros seismogenic layer. The seismogenic layer is that part of the earth's crust whose deformation is elastic, and the major fractures caused by the earthquakes occur in this part. In order to determine the attitude of the fault’sfocal plane, we use the focal coordinates of the earthquakes occurringaround each fault segment. In performing these calculations, the focal locations of the earthquakes are transferred to the geodetic coordinate system and, the equation of the fault plane is calculated using the least squares method in the Cartesian coordinate system. One can obtain the azimuth of the strike of the planes relative to the astronomical north by calculating the coefficients of the fault planes. To determine the azimuth, we first obtain the unit vector of the strike line by cross product of the geodetic z-axis (normal vector of the horizontal plane) and the normal vector of the fault plane. The fault plane azimuth will then be the angle between the strike line vector and the north vector.The north vector is the vector which is determined by connecting the point located on the center of each faultfragment to the intersection point of the horizontal plane and thez-axis. Variation in dynamic mechanisms of thefaults in the region creates fractures with different directions on the ground. We obtain theslip angle (rake) of the fault from the difference of the fault direction and the direction of thesurface fracture and the type of thefault (strike-slip, dip slip and oblique).By calculating the slip angle, we now calculate the unit vector of the slip direction from the rotation ofthe strike line vector as much asthe rake angle. Results & Discussion In order to calculate the slip rate of each fault, we consider Zagros crust as an integrated object, which deforms uniformly by imposing the stress. Based on this assumption, we project the velocity vectors of the Zagros geodynamic network on the fault planes and calculate the slip rates using the slip direction vectors. It should be noted that the velocity vectors of the geodynamic network have been defined in the navigation coordinate system. According to the definition of the fault plane equations, it is necessary to transfer the velocity vectors to the geodetic coordinate system. The resulting slip rate is a parameter which is calculated for each fault fragmentindividually. Considering the effect of the systematic errors in the focalposition of theearthquakes, (including the error of the focal depth and the epicenter location), the slip ratesobtained for the fault fragmentsalways have systematic errors. Therefore, we define an average slip rate for each fault in order toreduce the error effect. In this study, velocity vectors of seventeen permanent stations of the Zagros geodynamic network provided by the National Cartographic Center (NCC) are used. The focal positions of the earthquakes are also published by the International Institute of Earthquake Engineering and Seismology (IIEES). Conclusion The obtained results showed that the regions with high fault slip rate usually have dense earthquakes. In addition, the seismicity potential of any region can be found by comparing the slip rate of each fault and the density of its earthquakes in the region. According to the changes in the slip rate obtained in Zagros, faults in the western part of Zagros, especially in Ilam province, have low slip rates. However, the province is considered asone of the seismic areas of the state in terms of earthquake density.It means that most of the slip movements occurringon the faults of the western region have been accompanied by vibration.
narges fatholahi; Mehdi Akhoondzadeh Hanzaei; Abbas Bahroudi
Abstract
Extended Abstract
Land subsidence is a vertical movement of the earth surface relative to a stable reference level. It occurs as a result of plate tectonic and human activities. The common causes of subsidence from human activities are pumping under-ground water, oil and gas from overlying reservoirs. ...
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Extended Abstract
Land subsidence is a vertical movement of the earth surface relative to a stable reference level. It occurs as a result of plate tectonic and human activities. The common causes of subsidence from human activities are pumping under-ground water, oil and gas from overlying reservoirs. Withdrawal of fluids from hydrocarbon reservoirs causes their pressure to decrease. This pressure reduction rises the stress of reservoir’s overburden sediments which was previously controlled by the pressure of inside fluids before exploitation, and consequently increases the density of their porous surroundings. If the reservoir’s density exceeds a specific threshold, overburden rocks start to subside because of their weight. Therefore pressure drawdown leads to reservoir compaction, movement of the overburden and subsidence over the reservoir. This subsidence can prove costly for production and surface facilities. So study of the subsidence caused by hydrocarbon exploitation is an important task which needs precise considerations. Several methods are available to monitor land subsidence. Classical surveying such as Leveling and global positioning system (GPS) can produce some related data whereas they are expensive and cannot also produce the needed map at a particular period of time. Recent advances in satellite and Radar technology have made it possible to measure very small movements of the earth surface. Interferometric Synthetic Aperture Radar (InSAR) is a novel technology for measuring the surface deformation. Using the InSAR technique at relatively large subsidence areas can be monitored. The pros of InSAR are that it is not necessary to physically access the deformation areas and also the high spatial and temporal resolution of its data. Sub-centimeter accuracy has been reported for InSAR derived surface deformations. Interferometric Synthetic Aperture Radar relies on repeated imaging of a given geographic location by space-borne radar platforms. Synthetic Aperture Radar sensors measure both magnitude and phase of the transmitted electromagnetic signal that is backscattered from the earth surface. The phase measurement is used to derive information on heights and deformations of the terrain. This phase represents a combination of the distance scattering effect. If a second SAR data set is collected then from comparing the phase of the second image with the phase of the first, an interferogram can be formed. The basic principle of interferometric SAR is that if the surface characteristics are identical for both images, the phase differences are sensitive to topography and any intrinsic change in position of a given ground reflector. The interferogram can be corrected for topographic information using an external digital elevation model (DEM). The change in distance is along the line of sight to the satellite, preventing it from directly distinguishing vertical and horizontal movement. As geometrical and temporal baseline de-correlations and atmospheric noise are limitation factors to assess slow movements in subsidence areas, recent developments in multi temporal InSAR (MTI) algorithms have enabled the detection and monitoring of the slow deformation with millimetric precision. In this paper, Marun oil field; the second-largest oil field which is located in the south west of Iran has been studied. The Small Base Line Subset (SBAS) approach that is an (InSAR) algorithm has been performed for generating mean deformation velocity map and displacement time series from a data set of subsequently acquired SAR images. SBAS technique identifies coherent pixels with phase stability over a specific observation period which has been implemented in StaMPS software. This method which is based on multiple master interferograms, works with interferograms with small spatial baselines and short temporal intervals to overcome de-correlations by increasing spatial and temporal sampling and coherent areas. For this study, we have used 10 ASAR images acquired by the ENVISAT satellite from European Space Agency (ESA) during 2003 to 2006 and have generated 22 interferograms by the SBAS method. All interferometric processing were implemented using DORIS software. A SRTM Digital Elevation Model (DEM) with 3-arcsecond geographical resolution has been used to remove the topographic phase. SBAS processing was then implemented using the Stanford Method for Persistent Scatterers (StaMPS) software. As a result, the mean velocity map obtained through InSAR time series analysis which is in the Line-Of-Sight (LOS) direction of satellite to the ground. The time series analysis results of InSAR have been then compared with field production data. This sampled data allows us to evaluate potential of non-tectonic effects such as petroleum extraction on surface displacements and the relationship between both deformation and oil production rate. The results of InSAR analysis reveal the maximum subsidence on order of 13/5 mm per year over this field due to the extraction and geological characteristics in the time period of 2003-2006.
Hojat Shirmard; Abbass Bahroudi; Amir Adeli
Abstract
Due to the costly and time consuming drilling operations andits high risk of mineral exploration, this stage is of great importance.In order to determine optimum drillingpoints, it is essential to prepare a mineral potential map using the Geographic Information System(GIS), to integrate all exploratory ...
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Due to the costly and time consuming drilling operations andits high risk of mineral exploration, this stage is of great importance.In order to determine optimum drillingpoints, it is essential to prepare a mineral potential map using the Geographic Information System(GIS), to integrate all exploratory factors.Various methods have been developed for preparing the potential mapso far. One of the most effective ones, considering the nature of the geological and mineral phenomena, is the hierarchical method (AHP) in combination with fuzzy logic.In this research, a combined method consisted of hierarchical and fuzzy methods has been used under the name of fuzzy analytic hierarchy (FAHP). In this study, GIS technology has been used as one of the most effective tools for data and exploratory information management for the integration of various data in order to prepare the mineral potential map. In this research, the Naysian Porphyry copper deposit was used as a case study, because this mine, located in Isfahan province on the Uromieh-Dokhtar Volcanic belt of the country, has been under exploratory study, and because of the geological and mineral complexities, the optimal location of drilling sites has a significant sensitivity for detailed studies.The main purpose of this study is to determine the optimum drilling location using FAHP methods. To produce geological, geochemical factor maps, all available data of the Naysian copper deposit have been collected and analyzed. Fuzzy hierarchical process is used to calculate the weight of exploration layers and to implement this precisely, the geological and geochemical experts are used. In the process of integrating the resulting information layers in the GIS, fuzzy operators are used, and to evaluate and validate the obtained mineral potential map, the exploratory boreholes are used. Comparing the generated potential map with the boreholes shows a significant and positive adaptation between suggested drilling locations resulted from this study and the previous drillings. In this regard, the proposed points for the required drilling are provided.
