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801.
Two magnetotelluric (MT) surveys were carried out on the Mt. Etna volcano after two of the most intense eruptions of the last 30 years which took place in summer 2001 and winter 2002–2003. Surveying was pursued for two main reasons. First, we sought to contribute to the definition of the first-order structure and physico-chemical state (temperature, fluids, melts) of a volcano that has been extensively explored and monitored by means of various geophysical methods, but where only few electrical and electromagnetic surveys have been performed. Secondly, we acquired MT data in the same sites in the two different surveys with the aim of monitoring the possible changes of the first-order structure, since conditions are expected to vary on an active volcano such as Etna, and are supposed to be linked to the eruptive events. Soundings have been acquired in an E-W 10 km-long profile across the southern flank of Mt. Etna, at a distance of almost 6 km south from the Central Crater. The first survey was carried out three months after the 2001 eruption. Inverse models define a pronounced (4 km thickness) low resistivity section at a depth of about 1 km b.s.l. to the west. To the east, a low resistivity section is still present, but appears deeper, thinner and more resistive, and a shallow low resistivity anomaly also exists. The shallow anomaly to the east is tentatively correlated with altered and clayey volcanic units and/or temporary groundwater storage. The deep anomalies are interpreted as being due to melt storage at shallow depths which was not exhausted during the eruption. This would be confirmed by the abundance of lava erupted within one year from the end of the survey. The few good sites retrieved in the second survey, carried out a few weeks after the eruption of 2002–2003, confirm the picture defined in the first survey, and provide a better definition of the bottom of the deep anomaly located in the sedimentary basement. 相似文献
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803.
在实测资料和前人研究的基础上,引入“空代时”假说,分析研究了丹江口建库后汉江下游河流再造床过程的时空演替现象。分析表明,河流再造床过程在冲刷延展、河床粗化、含沙量及其特征、岸滩侵蚀以及河型变化等方面具有较典型的时空演替现象。产生时空演替现象的根源在于河流自调整作用在同一变源下空间和时间响应的一致性,是过程的相似。输入水沙条件的变化、水库下游河道支流入汇、河床边界条件的变化以及因此导致的不同调整方式是引起时空演替复杂响应的主要原因。如能排除干扰、建立时空演替现象的数学模式将有助于水库下游河流调整的分析和预测。 相似文献
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806.
This paper compares the performance of seven disaggregation models, based on various approaches and/or concepts, for the generation of 10-min time step rainfall series from hourly rainfall series. The so-called constant disaggregation model and a linear model based on the external temporal pattern of rainfall are first considered. The other models are stochastic: the first ones are based on a given probability density function applying for the 10-min rainfall amounts of the hour to disaggregate. This probability density function is either uniform or derived from the external temporal pattern of rainfall. The other stochastic models are scaling models using canonical or microcanonical multiplicative random cascades. The comparison of the models is based on their ability to reproduce some important statistical characteristics of the observed time series: variance, skewness coefficient, wet/dry properties of 10-min rainfall amounts; rainfall amounts quantiles for different return periods; autocorrelation of 10-min rainfall amounts. A continuous hydrological simulation is next applied to produce for each generated rainfall series a continuous discharge series used afterwards for a retention design. The ability of the different disaggregation models to produce rainfall time series resulting in the same retention design than the one obtained with the observed rainfall series is finally analysed. Deterministic models as well as simpler stochastic models have rather bad performances when compared to the others. Because it is non-conservative, the model based on a microcanonical random cascade performs also very poorly. It significantly overestimates all studied statistics. Models based on microcanonical random cascades achieve the best performance. They perform reasonably well for the reproduction of rainfall statistics and almost perfectly for the reproduction of runoff and storage design variables. Results finally highlight the interest of including in the disaggregation scheme information related to the external temporal pattern of rainfall. 相似文献
807.
新疆克拉玛依中基性岩墙群形成力学机制及其构造意义 总被引:13,自引:0,他引:13
克拉玛依岩墙群产出在克拉玛依北岩体及其围岩之中,具有不连续分段岩墙和连续分段岩墙两种类型,空间分布受区域张性构造裂隙控制,总体走向以北西-南东(280°~300°)为主,还有少量北东-南西(30°~50°)走向的岩墙。克拉玛依岩墙群所受最大主压应力方向垂直于地表,最小主压应力方向与岩墙扩容作用方向平行,并垂直于北西-南东走向的分段岩墙。岩浆沿构造裂隙贯入、充填形成岩墙,其发育程度与裂隙和区域各主压应力之间的夹角有关。岩墙分段的力学原因是岩浆在流动过程中,遇到与最小主压应力斜交的先存裂隙时,应力强度因子瞬间降低所致。估算的主伸长度为2.7%。克拉玛依岩墙群的大量出现进一步表明,二叠纪时,区域构造已经由碰撞挤压体制转变为伸展体制。 相似文献
808.
The Monegros playa-lakes are isolated saline wetlands, locally named ‘saladas’, situated in a vulnerable semi-arid territory where agricultural expansion threatens the natural hydrologic cycle with regular artificial flooding, risking the survival of a valuable natural resource. This study aims to examine the water regime of these playa-lakes from climate data and available hydrologic records. These records are historical and limited to a series of weekly measurements of depth and of water extent extracted from Landsat imagery. We have characterized the hydrological behavior of the playa-lakes by treating ground and satellite data separately. For this purpose, the playa-lakes are first grouped according to the water occurrence episodes. Then their hydrologic status is related to the previous rainfall and also to ET0, since there is a lack of local records of wind as well as brine or fresh water evaporation. The northern playa-lakes respond to rain faster than the southern ones. All playa-lakes have a significant relationship between water occurrence and rainfall accumulated within 180 days prior to an observation. A significant relationship between ET0 and water occurrence was found for a shorter 15-day accumulation period. Quantifying the current water regime now is critical for monitoring the effects of expanding irrigation in adjacent lands. Remote sensing is well-suited to an environmental assessment for regions of difficult access with the added benefit of lowered field measurement cost. The hydrological data from the Monegros playa-lakes could be integrated with other playa environments worldwide to compare regionally specific climate conditions. 相似文献
809.
两种新的水文频率分布模型:Pareto分布和Logistic分布 总被引:2,自引:0,他引:2
介绍了两种新的水文频率分布模型——Pareto分布和Logistic分布,分析了它们的统计特性和应用概况,制作了两种分布的离均系数表,能用一般的方法估计参数和设计值,可作为进一步研究频率曲线线型时的参考。 相似文献
810.
本文介绍在《超短波通信电路设计手册》的基础上,如何考虑设计中的抗干扰措施,这些措施包括:从抗干扰要求出发,调配系统方程参数;选择合适的工作频率;选择有利于抗干扰的设备技术指标;发挥天线的抗干扰作用。在通信电路设计中采取的抗干扰措施,和改善设备的抗干扰措施,是水文遥测系统抗干扰的两个重要方面,缺一不可,系统设计者应该引起充分注意。 相似文献