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991.
Ali A. Nowroozi 《Pure and Applied Geophysics》2010,167(12):1459-1474
The active faults near Tehran are capable of producing Mw magnitudes of 6.62?C7.23; at epicentral distances of 25?km from the active faults, and Mw?=?7.23, the peak ground horizontal acceleration, PGH, is between 386 and 730?cm/s2 and peak ground vertical acceleration, PGV, is between 192 and 261?cm/s2; the historic earthquake of the fourth century BC, Mw?=?7.16 produced the highest estimated PGH acceleration in Tehran, between 254 and 479?cm/s2 and PGV acceleration between 127 and 173?cm/s2. Earthquakes from 1909 to 2008, within 300?km from Tehran, are used for calculation of magnitude frequency relation, and results are applied to estimate PGH and PGV accelerations as a function of magnitudes for a set of fixed epicentral distance and site conditions; also as a function of epicentral distances for a set of fixed magnitudes and site conditions. Poisson??s distribution is used for probability calculation of PGH and PGV accelerations for several exposure times, site conditions and epicentral distances; accelerations with very high probability, near 1, are presented. At an epicentral distance of 10?km and exposure time of 450?years, in the northern part of Tehran, close to Mosha and the Northern Tehran faults, PGH acceleration is 800?C420?cm/s2 and PGV is 400?C220?cm/s2 with high probability. At an epicentral distance of 25?km and 1,000?years exposure time, PGH is 610?C320?cm/s2 and PGV is 310?C160?cm/s2 with high probability, where larger values are for soft soil and smaller values are for hard rock. 相似文献
992.
塔里木盆地大气降尘变化特征及影响因素分析 总被引:4,自引:2,他引:2
利用哈密、塔中与和田沙尘暴观测站2005—2008年大气降尘观测资料,结合铁干里克、民丰等18个大气降尘监测点2007年4月以来的大气降尘、沙尘天气等观测资料,分析了塔里木盆地大气降尘变化特征,同时分析了影响大气降尘浓度变化的主要因素。结果表明:①2005—2008年3站中哈密大气降尘量最少,其次为和田,塔中的大气降尘量最多; 2006年是4 a中降尘量最多年份,其次为2005年,2008年相对较少。②春夏季是大气降尘集中季节,秋季略大于冬季。塔里木盆地中部最高,南部及西南部的站点降尘明显高于盆地的东部和西部。③在沙尘暴季节,无论是5月还是6月,2007年大气降尘量基本上都高于2008年。④2007年5月和6月,除盆地东面的哈密、铁干里克以及西缘的阿拉尔3站外,其他18个站沙尘天气较多。沙尘天气是塔里木盆地大气降尘量高的主要因素,沙尘天气越多,大气降尘量越高。 相似文献
993.
古尔班通古特沙漠积雪覆盖、沙尘天气特征及其相互关系 总被引:2,自引:0,他引:2
利用TERRA/MODIS MOD10A2雪盖产品数据和地面观测积雪日数、冻土深度和沙尘天气日数等数据,从不同时间尺度分析古尔班通古特沙漠地表积雪覆盖与沙尘天气的特征及其相互关系。结果表明:①沙尘天气主要发生在4—10月,春季(4—5月)沙尘天气最多,夏秋季逐渐减少。从年际变化看,20世纪80年代前,沙尘天气发生日数呈逐年增加趋势,而积雪日数增减波动较大,二者间关系不明显,80年代后,沙尘天气逐年减少,积雪日数呈波动增加趋势。②冬春季积雪覆盖率、≥1 cm积雪日数、≥5 cm积雪日数、≥10 cm积雪日数与翌年春季沙尘天气发生均呈显著负相关关系,冬春季≥1 cm积雪日数每超过常年平均积雪日数1 d,翌年春季沙尘天气日数则减少4.3 d,而平均冻土深度与沙尘天气呈显著正相关关系。③积雪覆盖使沙漠地表形成冷源性下垫面和近地层逆温层结,增加了大气稳定度,同时春季积雪消融增加了土壤湿度,为荒漠植被生长提供充足的水分,使表层土壤为强风提供沙尘的可能性降低,从而对沙尘天气的发生起到阻碍、消弱作用。 相似文献
994.
As the Iranian seismic code does not address the soil–structure interaction (SSI) explicitly, the effects of SSI on RC-MRFs are studied using the direct method. Four types of structures on three types of soils, with and without the soil interaction, are modeled and subjected to different earthquake records. The results led to a criterion indicating that considering SSI in seismic design, for buildings higher than three and seven stories on soil with Vs<175 m/s and 175<Vs<375 m/s, respectively, is essential. A simplified procedure has been presented, on the basis that lateral displacement increments could be applied to the fixed-base models using simple factors. 相似文献
995.
According to the concept of “natural flow regime,” introduced and developed in the 1990's in aquatic ecology, streamflow can be described using five basic characteristics: magnitude, frequency, duration, period of occurrence and variability. A sixth could be added to these, namely, distribution curve. Our study, which focused exclusively on the temporal variability of these six characteristics, had these objectives: (1) to compare their stationarity, (2) to determine the links among these characteristics and (3) to analyze, for the first time, their relationship to six climatic indices (Atlantic Multidecadal Oscillation, Artic Oscillation, North Atlantic Oscillation, Niño3.4, Pacific decadal Oscillation and Southern Oscillation Index). To do this, we used the Vermillon River (2670 km²) as an example, analyzing the streamflow of heavy spring floods (equal to or greater than the annual flood streamflow), as measured between 1934 and 2000. 相似文献
996.
Comparison of ordinary kriging and artificial neural network for spatial mapping of arsenic contamination of groundwater 总被引:3,自引:2,他引:1
Mohammad Chowdhury Ali Alouani Faisal Hossain 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(1):1-7
In this technical note, we investigate the hypothesis that ‘non-linearity matters in the spatial mapping of complex patterns of groundwater arsenic contamination’. The spatial mapping pertained to data-driven techniques of spatial interpolation based on sampling data at finite locations.
Using the well known example of extensive groundwater contamination by arsenic in Bangladesh, we find that the use of a highly
non-linear pattern learning technique in the form of an artificial neural network (ANN) can yield more accurate results under
the same set of constraints when compared to the ordinary kriging method. One ANN and a variogram model were used to represent
the spatial structure of arsenic contamination for the whole country. The probability for successful detection of a well as
safe or unsafe was found to be atleast 15% larger than that by kriging under the country-wide scenario. The probability of
false hopes, which is a serious issue in public health monitoring was found to be significantly lower (by more than 10%) than
that by kriging. 相似文献
997.
Ali Olad Ali Reza Amani‐Ghadim Mir Saeed Seyed Dorraji Mohammad Hosein Rasoulifard 《洁净——土壤、空气、水》2010,38(4):401-408
The removal of Alphazurine FG (AF) dye from water by an electrocoagulation process has been studied. The effect of some operational parameters, such as anode material, current density, initial dye concentration, pH of solution, conductivity, and inter‐electrode distance, on the removal efficiency was investigated. Iron and aluminum were used as anodes in the electrocoagulation cell. It was found that the efficiency of the iron anode was better than that of the aluminum anode for AF removal. The factors that affected the removal efficiency were the current density and the initial dye concentration. The removal efficiency increased from about 35% at 25 A m–2 to about 97% at 100 A m–2, during 4 min of electrocoagulation. The results exhibited pseudo‐first‐order kinetics for AF removal by electrocoagulation. In addition, a mathematical model was successfully established for predicting the removal efficiency. A comparison between the model results and experimental data gave a high correlation coefficient (R2 = 0.9925), which indicates that the model is able to predict the removal efficiency of AF. 相似文献
998.
With a view to difficulties with explaining the physical mechanism of solar forcing on the Earth’s climate, we applied a new
approach of determining and quantifying an influence of solar-related events on water vapor variability by correlating the
total electron content (TEC) and precipitable water vapor (PWV), both derived from ground-based GPS observations.
In this study, ionospheric TEC and atmospheric PWV values are employed as solar activity and terrestrial climate parameters,
respectively. Three-year GPS data at five stations in Antarctica are analyzed on a daily mean basis. Results show significant
correlation between TEC and PWV differences during storms-affected days. The high correlation between the daily mean values
of TEC and PWV, both of which follow the seasonal signals and subsisting downward trend, suggests an influence of solar activity
on climate variability in Antarctica. These quantities are determined by changes of the upper-atmosphere level, which varies
in conformity with the zenith angle of the Sun. 相似文献
999.
Mariyam Sheibi Dariush Esmaeily Ann Nédélec Jean Luc Bouchez Ali Kananian 《Island Arc》2010,19(2):292-312
The Jurassic Shir‐Kuh granitoid batholith in Central Iran intrudes Lower Jurassic sandstones and shales. The batholith consists of three main facies: (i) a granodioritic facies to the north; (ii) a monzogranitic facies spread throughout the batholith; and (iii) a leucogranitic facies along the northwestern margin. The granodiorites are composed mainly of plagioclase, quartz, K‐feldspar, biotite, and some muscovite, garnet, cordierite, ilmenite, zircon, apatite, and monazite. This facies contains variable amounts of restite minerals which are mainly defined by calcic plagioclase cores and small aggregates of biotite. The monzogranites, with mineral assemblages similar to those in the granodiorites, range from relatively mafic (cordierite‐bearing) to felsic (muscovite‐rich) rocks. The leucogranites, exposed as small stock and dykes, consist mainly of quartz, K‐feldspar, and sodic plagioclase. The batholith is peraluminous, calc‐alkaline, and typical of S‐type, as indicated by Na2O content (2.74%), molecular Al2O3/(CaO + Na2O + K2O) (A/CNK) ratio (1.17), K2O/Na2O ratio (1.39), and isotopic data ([87Sr/86Sr]i = 0.715). The rocks are characterized by enrichment in large ion lithophile elements such as Rb, Th and K and depletion in high field strength elements such as Nb and Ti. Chondrite‐normalized rare earth element (REE) patterns are characterized by light rare earth element (LREE) enrichment, with values of (La/Yb)N between 4.5 and 19.53, unfractionated heavy rare earth element (HREE) with values of (Gd/Yb)N between 0.98 and 2.88, and a distinct negative Eu. The parental magma of the Shir‐Kuh Granite was derived from a plagioclase‐rich metasedimentary source (local anatexis of metagreywacke) in the crust, with heat input from mantle melt components. The separation of restite crystals from the primary melt followed by the fractional crystallization appears to have been an effective differentiation process in the batholith. 相似文献
1000.