جستجوی مقالات مرتبط با کلیدواژه "بعد فرکتالی" در نشریات گروه "زمین شناسی"

During the last two decades, the south part of seismotectonic zone of Zagros (Fars) was active. The Zagros seismotectonic belt consists of a series of fault-related folds that within their evolution, seismic areas and hydrocarbon reservoirs formed. Although the characteristics of Zagros are well known, the distribution of active deformations, style of fault-related folds, and its seismotectonic behavior are among the features that require further investigation.    In this study, changes in seismic rate based on changes in seismic parameter (b-value) and fractal dimension of seismicity (D-value) have been investigated using instrumental seismic data in the period of 2000 to 2021. Total amount of b-value and D-value were calculated by the least square’s method and the correlation integral method, respectively. The map of these parameters was plotted by interpolation method.    Frequency-magnitude distribution power law (logN=a–bM) relates the cumulative number of earthquakes (N) to their magnitude (M). This ratio is frequently used in seismic studies. In this relationship, a-value describes the productivity and b-value characterizes relative size distribution of earthquakes. Most b-value studies associate the seismicity parameter with the physical properties of a particular zone.    Since the introduction of fractal in 1976, the fractal concept has covered a wide range of pure mathematics and many experimental aspects of engineering. It has found a comprehensive concept. We analyzed seismicity using the IIEES and IRSC catalog. Decreasing the b-value in the northeastern of study area indicates that stress is increasing, which may signal a future sizable earthquake. The spatial variation of b-value suggests that the SW segment is less stressed compared to the NE segment.Considering that the correlation coefficient is about -0.78, the probability of occurrence of large earthquakes on large area faults increases. The zoning map parameter b-value to D-value ratio found valuable information on the invariance property of the seismic variation scale in the area. These results suggest that this approach can be used as a useful tool to evaluate seismic power distribution on active seismotectonic regions.    According to the zoning maps and the identification of high stress zone in the study area, the north parts of MFF, around Jam and Farashband and in the later stages, Khormuj will be the main candidate areas for future earthquakes. The seismicity pattern analyzed does hold the key to understand the seismotectonics of the region.

Jalal Abad iron deposit is located in 38 km northwest of Zarand city with about 200 million tons of iron ore reserves with an average grade of 46.2% iron, 0.98%, sulfur and 0.07% phosphorus. It is one of the seven important iron deposits of central Iran. The rock types of this area include low-sulfur oxide high-grade iron ore, sulfur-containing high-grade iron ores and low-grade silicate magnetite iron ores. Separation of mineralized zones based on the extent of ore and geological gangues is important for mine planning and drilling operation in mines. The main purpose of this study is the separation of mineralized zones based on the frequency and spatial expansion of mineral ores and gangues using fractal modeling in the deposit. The concentration-volume (C-V) fractal model was used for iron, sulfur and phosphorus in this deposit. These results showed that the main mineralized zones have a grading range as Fe ≥ 51, S ≤0.7 and P ≤0.4%. The fourth and fifth populations obtained by the iron block model are related as the main ores. Gangues and weakly mineralized zones also indicated at the first and second zones. Finally, optimal decisions can be made based on economic changes related to time and market conditions, for the third zone.

Fractal analysis of earthquakes, lineages and waterways are considered as one of the practical tools to evaluate tectonic activity. With the help of fractal analysis, structural maturity and tectonic dynamics can be evaluated. In this research, using fractal analysis and box counting method and fild studies, the measured fractal dimensions for the designed network of Alborz province were studied and compared. This network consists of 65 square meters with a side length of 12.5 km, for which the fractal dimensions of earthquakes, lines and waterways were calculated separately for all of them. The results of fractal analysis of lineages and network of waterways show high structural activity around Alamut, Mosha, north of Tehran and Taleghan faults located in the northern part and Ipak and Eshtehard faults in the southern part of the study area. In addition, due to the diversity of lithology in the study area, fractal analysis of earthquakes was performed and areas 54, 55, 45 and 46 have high tectonic activity, which these results only in the fractal analysis of earthquakes. Showed. In general, it seems that tectonic activity in Alborz province is strongly affected by the activities of major faults and, of course, the presence of sub-hidden faults (south of Alborz province) in the region, which was found in the analysis of fractal dimensions of earthquakes.

In this study, the concentration-number fractal method was used for regional exploration studies, and determining the anomalies of copper, lead and zinc elements. For this purpose, 800 samples of stream sediments were selected from the rivers in the area (i.e. from Kahak and Aran geological maps, 1: 100,000 sheets) and then the anomalies of these elements were mapped. The results show that strong copper anomalies are observed in the northern, central, southern and western parts of the area and the highest lead anomalies are located in the western part of the area. Strong anomalies of the zinc element are located in the central, southern and western parts of the region. These anomalies coincide with the lithological units of andesitic- basalt lava, volcanic breccia, tuffs, dacites, small scale masses of quartz -diorite, and small-scale masses of quartz-monzonite. The obtained map from combining anomalies and faults map reveals that the anomalies are mostly concentrated in fault zones and fault intersection points in the area and faults play a fundamental role in ore mineralization.

Shotori active fault zone (in the northern end of Nayband fault) has a dextral strike-slip mechanism with a revers component. Landsat image studies show that this fault is uncontinuous and segmented. In this research, based on fault geometric discontinuity, two segments, were determined on both the northern (with trend of N40w) and southern segments (with trend of N20w). Both of them are reverse with a right lateral slip movement component. The southern segment is the most active segment, based on fractal earthquake and fractal fractures (Ds= 1/60, DN=1/73) and earthquakes (Ds=0/43, DN=0/68) morphotectonic parameters such as river slope indicator (SLs=1703/27,SLN=1526/7), sinuosity river channel (SS=1/24,SN=1/27), the V ratio (Vs=0/7,VN=0/9) and structural and seismic data. The most frequent recorded earthquakes and the biggest registered earthquake with a magnitude of 7.4 on the Richter scale have taken place in the southern segment. This indicates a high potential of seismic activity on this segment of the Shotori fault.

  The East Azarbaijan geothermal area is located in northwest of Iran, which hosts several hot springs. It is situated mostly around the Sabalan and Sahand mountains. The Sabalan and Sahand geothermal area is now under investigation for the geothermal electric power generation. It is characterized by high thermal gradient and high heat flow. In this study, our aim is to determine the fractal parameter and top and bottom depths of the magnetic sources. A modified spectral analysis technique named “de-fractal spectral depth method” is developed and used to
estimate the top and bottom depths of the magnetized layer. A mathematical relationship is used between the observed power spectrum (due to fractal magnetization) and an equivalent random magnetization power spectrum. The de-fractal approach removes the effect of fractal magnetization from the observed power spectrum, and estimates the parameters of the depth to top and depth to bottom of the magnetized layer using iterative forward modelling of the power spectrum. This approach is applied to the aeromagnetic data of the East Azarbaijan Province. The obtained results indicated variable magnetic bottom depths ranging from 9.8 km to about 16.8 km. In addition, the fractal parameter was found to vary from 1.6 to 3 within the study area. The interpretation of potential fields is generally carried out in the frequency domain due to (1) simplicity in the implementation of signal processing tools, and (2) easy and concise characterization of potential field signals caused by a large variety of source models. In the frequency domain, the geophysical source parameters such as density have been assumed as uncorrelated distribution. To the contrary, source distribution of the physical parameters is correlated following the scaling or fractal laws. Fractal source distributions have power spectra proportional to , where k is the wave number (i.e. length of the wave vector) and β denotes the respective fractal parameter. This has been discovered by the detailed analysis of the densities
and susceptibilities of several borehole data around the world including the German continental deep drilling program in southeastern Germany. The fractal parameter reflects the proportion of long and short wavelength variations of a signal. The higher the value of the fractal parameter, the stronger is the relative intensity of the long wavelength variations of the signal. The main objective of the current work is to develop an algorithm for estimation of the fractal parameter using a defractal spectral analysis of the aeromagnetic data from the study area in order to determine the bottom depths of magnetic sources. This approach for analysis of magnetic data assumes that the observed power spectrum is equivalent to the random magnetization model multiplied by the effect of fractal magnetization. It is believed that the de-fractal method can reduce the ambiguity related to the selection of fractal parameter to provide an estimate of bottom depths of magnetic sources more reasonable than the estimates using conventional methods. However, the ability of the de-fractal method has not been verified so much in practical exploration applications. Hence, in this work, an attempt has been made to use this approach to remove the effect of fractal magnetization from the power spectrum of real magnetic data to have a reasonable depth estimate of magnetic sources. In the last four decades, variations on several methods have been proposed and applied for estimation of the bottom depths (zb) of magnetic sources using azimuthally averaged Fourier spectra of magnetic anomalies. The mathematical formulae of these methods are based on assumptions of flat layers with particular distributions of magnetization, namely: 1) random (uncorrelated) magnetization models or 2) self-similar (fractal) magnetization model. The idea of using models with fractal magnetization distribution comes from the concept of self-similarity. The de-fractal method is based on the assumption that the observed power spectrum is adequately represented by a simplification of the fractal magnetization power spectrum where the magnetization in the x and y directions is fractal and is constant in the z direction. In this case, the observed power spectrum is equivalent to the result of power spectral density of the random magnetization model multiplied by k-α. Having removed the fractal effect, one can treat the resulting de-fractal power spectrum as though it was the power spectrum of a random magnetization model. The present approach can be considered as a correction to the power spectrum of the magnetic field for the fractal distribution of magnetization. In this work, we have determined the bottom depths to magnetic sources using de-fractal spectral analysis method. This method applies a transformation to the observed magnetic field based on an estimated fractal parameter such that the power spectrum resembles the power spectrum that would be generated by a random magnetization distribution. The advantages of this method are that the range of the feasible de-fractal parameters can be estimated, and the bottom depths of the magnetic sources or anomalies are obtained based on simultaneously estimating the depth values from the centroid method and visual inspection of the forward modeling of the spectral peak. The method has been applied to 50% overlapping 11 blocks having 100 * 100 square km dimensions of aeromagnetic data in Ardabil area. As a result, the fractal parameter has been determined between 1.6 and 3 The obtained results also indicate that the bottom depths of
sources of the magnetic anomalies vary from 9.8 km to about 16.8 km.

The multifractal modelling is an effective approach for separation of geological
and mineralized zones from the background. Following cases are addressed
in this study; Concentration-Distance to Major Fault structures (C-DMF) fractal model
and distribution of the known Fe indices/mines in the Bafgh area to distinguish the Fe
mineralization based on their distance to basement faults, surface faults and master
joints, using remote sensing information, airborne geophysics information and field
surveys. Application of the C-DMF model for the classification of Fe mineralization
in the Esfordi and Behabad 1: 100,000 sheets reveals that the main Fe mineralizations
have a strong correlation with their distance to the major and basement faults.
Accordingly, the distances of Fe mineralization that has the grades upper than 55% in
this area )43%≤S≤60%), are lower than 1 km related to basement faults, while such
distance for this threshold is 2344

Fractal analysis of drainages and fractures is a useful tool to determine the maturity structure of a region. With the help of fractal geometry, this study investigates the fractal dimension of drainages and fractures in the southwestern part of Lenjan, and examines the role of geological structures after determining the most active part of region. In order for fractal analysis of fractures and drainages, box-counting method has been used. To achieve this, four parts A, B, C and D of high structural density were first detected in the region, and the fractal dimensions of drainages and fractures were then calculated and compared. Results of fractal analysis of fractures suggest that sector B is the most active part of the region, while fractal analysis of drainages indicates greater tectonic activity in sector A. The larger number of earthquakes and higher density of fractures in sector B, however, could indicate it as the most active part of the study area. Therefore, contradicts in different results obtained from the fractal dimension analysis of fractures and drainages can be explained by the varieties in lithology. The structural studies indicate the existence of a dextral transpression zone in the study area. The dextral transpression zone resulted in uplift of sector B by development of positive flower structures in this part of the region. Therefore, increased tectonic activity in part B is due to formation of positive flower structures and consequent tectonic uplift.

Porous media such as groundwater aquifers, oil and gas reservoirs have a large amount of heterogeneity. Modeling of flow and transport in such environments is based on a survey of the properties of porous media. In this paper, fractal permeability of porous media has been estimated using the Monte Carlo simulation. Using the results of previous studies and measurements on several sandstone samples, such as porosity, fractal dimension, fractal property and intrinsic permeability, using a Monte Carlo probabilistic model and a set of random numbers between 0 and 1 and pore diameter measurement, the sandstone permeability was determined. Finally the simulated and measured values of samples sandstone permeability were compared. Monte Carlo simulation results show that without any need for empirical coefficients, domain discretization with only a few laboratories measured parameters one can reasonably determine the fractal permeability of porous media. Measured and calculated permeability correlations are matched 83 percent.

Baladeh-Kojour earthquake of May 28th, 2004 is one of the largest earthquakes in vicinity of Tehran, occurred in the northern part of the Alborz range. In this research, spatial variation of fractal parameters has been studied to estimate the seismic pattern of the study area. In order to draw the spatial variation maps, b-value, correlation dimension of epicentral and temporal distribution of earthquakes, De and Dt have been calculated for the data sets of before and after the mainshock, separately. The results show that before the earthquake, these parameters have low values in the eastern side of the mainshock epicenter. It seems that these low values before the earthquake may arise due to clusters of events with larger magnitude and small events after it. Seismic rate has decreased in the surroundings of the mainshock (seismic quiescence). After the mainshock, the lowest values of b-value and Dt is seen in the epicentral and western part of the mainshock. These low values are due to aftershock clustering and stress release, took placed just after the mainshock and during the aftershock sequence. Intensity increasing is observed in the shake map of earthquake. The De parameter is low after the mainshock occurrence. Low b-value and high De indicate high level of seismic activity in the region. The obtained results show the fractal parameters sensitivity to spatial and temporal clustering of earthquakes. Therefore, these parameters can be used as an indicator for seismic precursory patterns of major earthquakes.

In this study active faults in the region of Shahid Rajai dam of sari with 100 km radius was categorized on based fractal dimension of faulting and Earthquake and also evaluating of slip rate and investigate those activity rate. Using the fractal dimension of faulting and earthquake with squares method (Box-counting) and finally by classification this fractals dimension، the faults of North Alborz، Damghan and Garmsar more activity faults in the region of study area during 100 years late which based on activity degree of faulting and Earthquake with method of fractal analysis which based on assessment of activity degree of faulting and earthquake with method of fractal analysis also set in BD grade and this activity was confirmation. For assessment of slip rate beginning the seismicity parameters (a&b) of study area was determination، then these parameters were normalized for each fault. Based on existing relationships and having a&b for each fault، the seismic moment those fault was calculated. According to The relationships for calculating the rate of seismic moment، slip rate of each fault has been estimate and based on faults in study area was classification. The Faults with very low slip rate and high return period of earthquake could cause occurrence large earhquakes which earthquake of 856 A. D Qumes and causing smith therefore Damghan Fault could this fault know. Thereupon Therefore expectance larger slip in the future on faults such as Astaneh، Rameh، Cheshme-Ali and etc Will have. High slip rate along the New faults introduced (Khorram-Abad، Majid، etc.) in this area is noteworthy that according to occurrence the earthquakes in the privacy of their fault، the high slip rate is reasonable.

In this research, to investigate seismic pattern and precursory properties of fractal dimensions, spatial distribution and temporal variations of correlation dimensions of epicentral, De, and temporal distribution of earthquakes, Dt, before the Baladeh-Kojour earthquake have been studied. The May 28th, 2004, Baladeh-Kojour earthquake with Mb= 6.2 (ISC), which is one of the largest earthquake in the vicinity of Tehran, was occurred in the northern part of the Alborz mountain ranges. The spatial distribution maps show decreasing in De and Dt in the eastern part of the epicenter, which is observed at 2002 in the temporal variation plots. With respect to space-time plot, it seems that this decreasing caused by the earthquake clusters that were occurred between 2002 -2003. Investigation of seismic pattern based on spatial and temporal variations of fractal dimensions and space-time plot of earthquakes demonstrate doughnut pattern (some earthquake clusters and a lot of small events) and seismic quiescence before the main shock. The results indicate that fractal dimensions are sensitive to clustering in space and time. So, the spatial and temporal variations of these parameters can be used as a precursory phenomenon, which is caused by seismic activation and quiescence.

The Azerbaijan experimented several seismic activities during its history, that sometimes these earthquakes caused significant damage to lives and property. Most seismic activity in Azerbaijan can be seen around the major fault systems that distributedin the clustering system in the NW-SE direction. Seismic behavior in a fault could be related to geometrical irregularities, regardless of the scale, this can be a function off ractal geometry and so these geometricalirregularities can be investigated in case of fractal dimension (D). Box counting method off ractal analysis was conducted in Azerbaijan. Based on our results, with receding from the main fault systemin there gion which has a NW-SE trend and distributed from the NorthWest to Centre of Azerbaijan, the fractal dimension decrease. This is reason for the existence of discontinuities in the fault systems in the region. High value of fractal dimension in Tabriz, Osku and Bostan Abad regions and also decrease in value of fractal dimension in Qare Chaman, Sarab and Mianeh suggests that the ending zone of main fault systems in Azerbaijan lying in region between Bostan Abad and Qare Chaman region. On fractal analysis of Azerbaijan faults and surviving seismic data, main seismic activities in Azerbaijan are related to major fault or their branches in region. Also distribution of volume and surface fractal dimension in Azerbaijan shows high seismic activity in central and NW regions than other adjacent regions.