Application of Principal Component Analysis and Spectral Angle Mapper in the Mapping of Hydrothermal Alteration in the Jebal–Barez Area,Southeastern Iran     

Mehdi HONARMAND  Hojjatollah RANJBAR  Jamshid SHAHABPOUR 《Resource Geology》2012,62(2):119-139

The southeastern part of the central Iranian Cenozoic magmatic belt contains many areas with copper mineralization. In an analysis of this region, we used the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Enhanced Thematic Mapper plus (ETM⁺) images to map the distribution of hydrothermally altered rocks, based on their mineral assemblages. The spectral measurements, based on the field samples and satellite‐image‐derived spectra, show dominantly Al–OH (sericite and clays) and Fe–O absorption features in the visible–near infrared to shortwave infrared regions of the spectrum. Silica–bearing rocks, as well as silicic alteration, show an intense Si–O vibrational feature in the thermal infrared wavelength region. We analyzed ASTER/ETM⁺ images, performed a directed principal component analysis, and used spectral angle mapper to map areas of hydrothermal alteration and iron oxide/hydroxide minerals. The individual principal component images compiled by directed principal component analysis reveal the distribution of individual alteration minerals such as sericite, kaolinite, chlorite, epidote, and quartz. The best results, in terms of mapping the distribution of alteration, were obtained using the spectral angle mapper method. The altered areas were then sampled and the samples subjected to X–ray diffraction analysis, spectral analysis, and thin sections were observed under a microscope. Field observations reveal that more than 98% of the known copper mineralization occurs within the interpreted alteration areas. The present results indicate the great potential of ASTER and ETM⁺ data for mapping the distribution of alteration and exploring for copper mineralization in areas with a similar climate and geological setting to those of the present study.  相似文献   

The 27 August 2010 Mw 5.7 Kuh-Zar earthquake (Iran): field investigation and strong-motion evidence     

Mohammad P. Shahvar  Mehdi Zaré 《Natural Hazards》2013,66(2):689-706

In this study, seismological aspects and field observation of the 2010 Kuh-Zar earthquake has been investigated. The Kuh-Zar earthquake, of magnitude 5.7 (Mw), occurred in northeastern Iran on August 27, 2010. The area is surrounded by branches of the active faults which are coated by the quaternary alluvium. During the past several decades, this area has been struck by a number of earthquakes. This earthquake with a moderate magnitude caused a higher rate of damage contrasted with previous earthquakes of the same magnitude range in Iran. Fortunately, the source of the Kuh-Zar earthquake was in a sparsely populated area, and therefore, it caused a few loss of life with the highest observed intensity of shaking VII (modified Mercalli intensity) in the Kuh-Zar village. The shock killed 4 people, injured 40, and destroyed more than 12 villages. According to the field observation, the mechanism of this shock is defined as a left-lateral strike slip. We also checked out the properties of strong ground motions in this earthquake using the records availed by Iranian strong motion network. At KUZ station, about 7 km east of the epicenter, the recorded PGA and PGV in both horizontal and vertical components were remarkably large for an event of this size, and visual inspection of the velocity time history reveals a pulse-like shape. Unfortunately no other recording stations were located close enough to the fault to capture a directivity pulse. Finally, according to the strong-motion properties and observed information, ShakeMaps of the earthquake have been generated by the native intensity observations and the recorded strong motions.  相似文献   

Problematic Soft Soil Improvement with Both Polypropylene Fiber and Polyvinyl Acetate Resin     

Esmaeil Masoumi  Seyed Mehdi Abtahi Forooshani  Farzad Abdi Nian 《Geotechnical and Geological Engineering》2013,31(1):143-149

Several methods are used to improve mechanical properties of loose soils including rewetting, soil replacement, compaction control, chemical additives, moisture control, thermal methods, and more recently, discrete fibers. All the methods are applied to soft soil to increase load bearing capacity and to improve other properties such as prevention of erosion and dust generation. In the present study, a new method of soil improvement using both discrete polypropylene (PP) fibers and polyvinyl acetate (PVAc) is introduced. The method is applied to improve load bearing capacity of a problematic sandy soil in both dry and saturated states. Based on the results from CBR tests on various specimens, it has been revealed that the combination of PP fiber and PVAc resin with weight percentages of 0.1 and 0.6 %, respectively, had the optimum effect in increasing the CBR value in both saturated and dry soil specimens. It should be mentioned that this method has caused a great increase in the CBR value in the saturated soil.  相似文献   

Spectral Combination of Spherical Gradiometric Boundary-Value Problems: A Theoretical Study     

Mehdi Eshagh 《Pure and Applied Geophysics》2012,169(12):2201-2215

The Earth’s gravity potential can be determined from its second-order partial derivatives using the spherical gradiometric boundary-value problems which have three integral solutions. The problem of merging these solutions by spectral combination is the main subject of this paper. Integral estimators of biased- and unbiased-types are presented for recovering the disturbing gravity potential from gravity gradients. It is shown that only kernels of the biased-type integral estimators are suitable for simultaneous downward continuation and combination of gravity gradients. Numerical results show insignificant practical difference between the biased and unbiased estimators at sea level and the contribution of far-zone gravity gradients remains significant for integration. These contributions depend on the noise level of the gravity gradients at higher levels than sea. In the cases of combining the gravity gradients, contaminated with Gaussian noise, at sea and 250?km levels the errors of the estimated geoid heights are about 10 and 3 times smaller than those obtained by each integral.  相似文献   

The PBRM (perception-based regional mapping): A spatial method to support regional development initiatives     

Mehdi Saqalli  Patrick Caron  Pierre Defourny  Ali Issaka 《Applied geography (Sevenoaks, England)》2009,29(3):358-370

This paper examines the relevance of a perception-based regional level mapping tool in rural Niger. Two regions in Niger are examined. Results permit to assume that such a tool helped to fill several gaps: (i) a scale gap between local and nation wide studies; (ii) a scientific gap between biophysical and socio-anthropological sciences; and (iii) a methodological gap of integration between data sources. Moreover, this method is fast, cheap and action-oriented. Data are easily understandable and usable both by rural communities and development agencies. It provides information about human dynamics at a regional level, which cannot be achieved by other methods.  相似文献   

A geoid solution for airborne gravity data   总被引：2，自引：0，他引：2  

Lars E. Sjöberg  Mehdi Eshagh 《Studia Geophysica et Geodaetica》2009,53(3):359-374

Airborne gravity data is usually attached with satellite positioning of data points, which allow for the direct determination of the gravity disturbance at flight level. Assuming a suitable gridding of such data, Hotine’s modified integral formula can be combined with an Earth Gravity Model for the computation of the disturbing potential (T) at flight level. Based on T and the gravity disturbance data, we directly downward continue T to the geoid, and we present the final solution for the geoid height, including topographic corrections. It can be proved that the Taylor expansion of T converges if the flight level is at least twice the height of the topography, and the terrain potential will not contribute to the topographic correction. Hence, the simple topographic bias of the Bouguer shell yields the only topographic correction. Some numerical results demonstrate the technique used for downward continuation and topographic correction.  相似文献   

Wavelet and Gaussian Approaches for Estimation of Groundwater Variations Using GRACE Data          下载免费PDF全文

Farzam Fatolazadeh  Behzad Voosoghi  Mehdi Raoofian Naeeni 《Ground water》2016,54(1):74-81

In this study, a scheme is presented to estimate groundwater storage variations in Iran. The variations are estimated using 11 years of Gravity Recovery and Climate Experiments (GRACE) observations from period of 2003 to April 2014 in combination with the outputs of Global Land Data Assimilation Systems (GLDAS) model including soil moisture, snow water equivalent, and total canopy water storage. To do so, the sums of GLDAS outputs are subtracted from terrestrial water storage variations determined by GRACE observations. Because of stripping errors in the GRACE data, two methodologies based on wavelet analysis and Gaussian filtering are applied to refine the GRACE data. It is shown that the wavelet approach could better localize the desired signal and increase the signal‐to‐noise ratio and thus results in more accurate estimation of groundwater storage variations. To validate the results of our procedure in estimation of ground water storage variations, they are compared with the measurements of pisometric wells data near the Urmia Lake which shows favorable agreements with our results.  相似文献   

Fracture characterization using converted waves          下载免费PDF全文

Mehdi E. Far  Bob Hardage 《Geophysical Prospecting》2016,64(2):287-298

We present a method for inversion of fracture compliance matrix components from wide‐azimuth noisy synthetic PS reflection data and quantitatively show that reflection amplitude variations with offset and azimuth for converted PS‐waves are more informative than P‐waves for fracture characterization. We consider monoclinic symmetry for fractured reservoir (parameters chosen from Woodford Shale), which can be formed by two or more sets of vertical fractures embedded in a vertically transverse isotropic background. Components of effective fracture compliance matrices for a medium with monoclinic symmetry are related to the characteristics of the fractured medium. Monte Carlo simulation results show that inversion of PS reflection data is more robust than that of PP reflection data to uncertainties in our a priori knowledge (vertically transverse isotropic parameters of unfractured rock) than PP reflection data. We also show that, while inversion of PP reflections is sensitive to contrasts in elastic properties of upper and lower media, inversion of PS reflections is robust with respect to such contrasts.  相似文献   

The dichotomous Markov process with nonparametric test application; a decision support method in long-term river behavioural analysis: the Zayandeh Rud River; a case study from central Iran   总被引：1，自引：1，他引：0  

Mehdi F. Harandi  Shantia Yarahmadian  Mohammad Sepehrifar  Pieter H. A. J. M. van Gelder 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(7):1889-1896

We use the Dichotomous Markov Noise model with constant transition rates to describe the dynamics of fluctuations in the water level as a stochastic process, which is imposed on river discharge changes. By applying this model, two different regimes are determined for the long-term behaviour of the river. Based on these regimes, we define two nonparametric classes of the overall increasing/decreasing nature of the water level in the long-term behaviour, which are separated by an exponential steady state regime. In this paper, we develop a nonparametric testing procedure to test exponentially (steady state regime) against an alternative overall decreasing level distribution. The proposed test predicts the long-term regime behaviour of the river. The mathematical tools introduced to handle the problem should be of general use and the testing procedure can be considered as a new mathematical tool in the study of water level dynamics. Under conditions of data austerity and as a case of study, we examine the stochastic characteristics of the Zayandeh Rud (Zāyandé-Rūd or Zāyanderūd, also spelled as Zayandeh-Rood or Zayanderood) River (Isfahan, Iran) water level.  相似文献   

Ground motion record simulation for structural analysis by consideration of spectral acceleration autocorrelation pattern   总被引：1，自引：1，他引：0  

Alireza Azarbakht  Mahdi Sadeghi  Mehdi Mousavi 《地震工程与工程振动(英文版)》2014,13(2):195-202

A novel approach is introduced to generate simulated ground motion records by considering spectral acceleration correlations at multiple periods. Most of the current reliable Ground Motion Record(GMR) simulation procedures use a seismological model including source, path and site characteristics. However, the response spectrum of simulated GMR is somewhat different when compared with the response spectrum based on recorded GMRs. More specifi cally, the correlation between the spectral values at multiple periods is a characteristic of a record which is usually different between simulated and recorded GMRs. As this correlation has a signifi cant infl uence on the structural response, it is needed to investigate the consistency of the simulated ground motions with actual records. This issue has been investigated in this study by incorporating an optimization algorithm within the Boore simulation technique. Eight seismological key parameters were optimized in order to achieve approximately the same correlation coeffi cients and spectral acceleration between two sets of real and simulated records. The results show that the acceleration response spectra of the synthetic ground motions also have good agreement with the real recorded response spectra by implementation of the proposed optimized values.  相似文献