1962年3月19日新丰江6.1级水库诱发地震时的构造应力   总被引：2，自引：1，他引：1  

官幼雄  李亚林  颜玉定 《华南地震》2005,25(3):83-86

对1962年3月19日新丰江MS6.1水库诱发地震震源附近的花岗岩质构造岩,进行三轴强度实验。根据实验结果,利用摩尔强度理论探讨该地震发震时的构造应力。研究表明:①1962年3月19日新丰江MS6.1水库诱发地震发生时,构造应力在震源处岩体断裂面上应力集中部位的剪应力已高达164MPa,为该处抗剪强度的97%;其它走向、倾向相似的无应力集中的断裂面上的剪应力(构造应力)约为18MPa。②在近代构造应力场中,新丰江岩体中只有走向在N30°±50°W范围内的断裂,才存在破裂的可能。  相似文献   

汶川大地震中土坝破坏程度与坝体几何形状的关系分析     

叶亚三  陈国兴  王志华 《地震工程与工程振动》2012,32(1):146-153

调查、搜集和研究了汶川地震中被评定为高危以上险情的147座小型水库土坝的地震破坏情况,给出了高危以上险情土坝的地震破坏程度划分为中等破坏、严重破坏和极严重破坏三个等级的原则和标准,以及土坝的地震破坏程度与地震烈度、土坝的宽高比、上游坡比、坝高的经验关系表,可发现:土坝的几何形状对其破坏程度起着重要的作用;对于6～8度地震烈度区,土坝的宽高比越小,或上游坡比越小,或坝体越高,则土坝的破坏程度越严重;对于9度以上地震烈度区,土坝通常发生极严重破坏。依据高危以上险情土坝的地震反应分析结果,给出了土坝地震破坏程度与土坝宽高比、坝高、土坝上游坡比及坝顶加速度放大系数、坝体最大动剪应力的经验关系曲线,发现在相同的地震烈度水平下,土坝的宽高比越小,或上游坡比越小,或坝高越大,且坝顶加速度放大系数越大或坝体最大动剪应力越大,则其地震破坏程度越严重;坝体最大动剪应力超过30kPa的土坝,通常发生严重或极严重破坏,坝体最大动剪应力大于100kPa的土坝,通常发生极严重破坏;土坝离发震断层越远,则其坝顶加速度放大系数越大。本文给出的高危以上险情土坝的地震破坏程度与坝体几何形状的经验关系,可为今后土坝抗震设计提供参考依据。  相似文献   

Hydraulics of a partially penetrating well with skin zone in a confined aquifer     

Gautam Barua  S.N. Bora 《Advances in water resources》2010

A steady/quasi-steady model is developed for predicting flow into a partially penetrating well with skin zone in a confined aquifer overlying an impervious layer. The model takes into account flow through the bottom of the wellbore, finite skin thickness and finite horizontal and vertical extent of the aquifer. Moreover, the solution can be easily extended to include the mixed-type boundary condition at the well face, where a Dirichlet in the form of a specified hydraulic head and a Neumann in the form of zero flux coexist at the same time at different portions of the well face. The validity of the proposed solution is tested by comparing a few results obtained from the developed model with corresponding results obtained by analytical and numerical means. The study shows that, among other factors remaining constant, both the horizontal and vertical extent of an artesian aquifer, thickness of the skin zone, bottom flow and conductivity contrast of the skin and formation zones, play an important part in deciding flow to a well dug in the aquifer, and hence these factors must be considered while analyzing the problem. The model proposed here can be used to estimate skin thickness as well as hydraulic conductivities of the skin and formation zones of a well with skin zone in an artesian aquifer underlain by an impervious layer by utilizing pumping test data falling in the steady or quasi-steady state of a typical pumping test. As the proposed solution is of a general nature in the sense that it can handle, apart from partial penetration and bottom flow, the finite size skin zone and finite horizontal and vertical extent of an artesian aquifer together with the mixed-type boundary condition at the well face, it is hoped that the predictions coming out of the model will be more realistic than those obtained using solutions developed with more stringent assumptions.  相似文献   

近30年来三江源地区土地覆被与宏观生态变化特征   总被引：16，自引：0，他引：16  

邵全琴  赵志平  刘纪远  樊江文 《地理研究》2010,29(8):1439-1451

利用1970年代中后期MSS图像和1980年代末、2004年以及2008年三期TM图像并结合野外调查,获得三江源地区四期土地覆被空间数据集,提出了土地覆被转类指数和土地覆被状况指数,以表征该区域生态变化的趋势。通过计算土地覆被转类途径和幅度、土地覆被转类指数和土地覆被状况指数,分析青海三江源地区1970年代中后期以来土地覆被时空变化特征及其反映的宏观生态状况变化。结果表明:三江源地区近30年平均土地覆被状况指数为38.20,土地覆被状况为4级,其中黄河流域最好,其次为澜沧江流域,长江流域最差;三江源地区土地覆被转类,在1970s~1990s和1990s~2004年两个时段,均主要以高生态级别向低生态级别转移为主,2004~2008年时段,主要以低生态级别向高生态级别转移为主;由土地覆被状况指数变化率和土地覆被转类指数,可以反映出近30年来三江源地区土地覆被和宏观生态状况,总体上经历了变差(1970s~1990s时段土地覆被状况指数变化率Zc为-0.63,土地覆被转类指数LCCI为-0.58)—显著变差(1990s~2004时段Zc为-0.94,LCCI为-1.76)—略有好转(2004~2008时段Zc为0.06,LCCI为0.33)的变化过程。这一变化过程前、中期主要受到气候变化和草地载畜压力共同驱动的影响,后期则叠加了生态建设工程的驱动作用。  相似文献   

环境背景数据的分类编码与应用   总被引：1，自引：0，他引：1  

刘劲松陈辉  高吉喜 《地球信息科学学报》2004,6(4):56-61

以环境背景数据为研究对象,通过对语义时间、存储格式、记载介质、负责机构、专题信息等属性特征的分析,提出完整的环境背景数据概念;强调环境背景数据的分类编码,应侧重环境背景数据的发现,并着重讨论分类编码的贯彻实施应以元数据为标准载体,在统一的环境背景数据分类编码无法确定时,利用核心元数据中的关键字字段实现分类编码的间接引用,确保元数据标准对不同系列分类编码的兼容并包。  相似文献   

Evaluation of floodplain variability considering impacts of climate change     

Mohammad Karamouz  Navideh Noori  Ali Moridi  Azadeh Ahmadi 《水文研究》2011,25(1):90-103

In this study, an approach is presented for handling hydraulic uncertainties in the prediction of floodplain. Different factors affect river flood characteristics. Furthermore, the high changeability of flooding conditions leads to high variability of the inundation. River morphology is one of the most effective factors in river flood characteristics. This factor is influenced by sedimentation and erosion in the river cross sections, which affects the discharge variation. The depth and the width of the river cross section lead to an increase or decrease in the river flow path. This results in changes in the extent of the floodplain based on the generated rainfall. The inundated region boundaries are determined by utilizing the mean first‐order second‐moment analysis. The proposed method is applied to the Kajoo River in the south‐eastern part of Iran. Determination of floodplain uncertainty is a damage‐reduction policy in this region. Also, it is useful to prepare the necessary activities for overcoming the flood hazards. Climate change is the second effective factor on the floodplain uncertainties. Climate change affects the magnitude, extent and depth of inundation and it may intensify the flood problem. Therefore, the future rainfall pattern of the study area under climate change is simulated to evaluate its impacts on the river flow characteristic. Subsequently, a hydraulic routing model is used to determine floodplain. Finally, the copula function is used to estimate the joint probability of the changes in the inundation area due to changes in river morphology and the rainfall changes due to impacts of climate change. Results show that the uncertainties of the extent of floodplain are affected by climate change and river morphology, leading to noticeable changes in the magnitude and frequency of floods. Evaluating these impacts and estimating corresponding river discharges will help in the study of river dynamics, and will also contribute towards devising effective mitigation and management strategies. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

2000—2020年中国荒漠化潜在发生范围区林草覆被时空变化特征     

李长龙  王燕  高志海  孙斌 《地理学报》2022,77(11):2803-2816

干旱地区林草植被生长动态变化是研究荒漠化形成发展和演变过程的重要依据。本文基于改进方向性像元二分模型构建的2000—2020年中国荒漠化潜在发生范围区（PEDC）年植被覆盖度数据集,采用Sen+Mann-Kendall时间序列趋势变化检测方法,分析了2000—2020年PEDC,特别是林草覆盖区的植被生长状况时空变化特征。研究结果表明：① 2000—2020年,PEDC平均植被覆盖度为0.284,改进的植被覆盖度估算结果能够较好地反映研究区植被覆盖状况,估算精度为86.98%。PEDC植被生长状况不断趋好,其中干旱区表现最为突出,显著增加区域达到了48%,而亚湿润干旱区平均增长量最大为0.1。② 林草生态恢复工程措施效果显著,但植被恢复是个长期缓慢的过程,特别是林草面积的恢复。2000—2010年林草面积增加较少（0.002%）;2010—2020年增加较多（0.371%）。③ 2000—2020年PEDC林地植被改善最明显,草地则较为稳定,植被覆盖度显著性增加区域分别为76.4%和71.8%。其中林地植被覆盖度在亚湿润干旱区增长量最大为0.15,而整个研究区草地增长了0.06。本文更深入地掌握PEDC林草覆盖区长时间序列植被生长状况,为进一步制定和实施各项生态工程提供重要信息参考。  相似文献   

The spatial extent and coverage of tornado sirens in San Marcos,Texas     

《Applied geography (Sevenoaks, England)》2015

The tornado siren has become the standard method of notifying resident populations of dangerous weather conditions. In March, 2012, the city of San Marcos, Texas purchased 14 Tempest-121 rotating sirens creating a coverage network. Because San Marcos has experienced two tornadoes during the previous twelve years, two research questions were constructed, 1) what is the spatial coverage of the tornado siren network in San Marcos, and 2) what is the approximate number of residents located outside the siren's network coverage area? The hypothesis stated that the siren network left more than 10 percent of the population outside the coverage area.Each tornado siren was individually located and associated GPS data allowed for construction of the siren network in a GIS. The analysis identified approximately 26 percent (22 km²) of San Marcos located outside the network's coverage area. Furthermore, analysis of census block data and the extent of siren coverage resulted in 5.14 percent of residents not included in siren coverage, approximately half compared to what was hypothesized. As San Marcos continues to expand, both in size and in population, the question of whether there is enough coverage for the entire city for the foreseeable future remains unclear.  相似文献   

Movement and variation of four typical glaciers in the Qilian Mountains, northwestern China     

ZheFan Jing  Kun Wang  Li Liu 《寒旱区科学》2015,7(3):206-211

We selected four typical glaciers in the Qilian Mountains and investigated their movements and variation using advanced technologies such as remote sensing,photographic measurements,and global positioning systems.The velocity of glacier movements in the Qilian Mountains is relatively low,and there has been no significant variation during the past 50 years.Glacier motion has maintained a normal style.The movement velocity of Laohugou Glacier No.12 presented a decreasing trend(by 48%) from 1960 to 2012.The movement velocity of the Qiyi Glacier also presented a decreasing trend(by 48.1%) from 1958 to 2012; it decreased by 29.4% from 1958 to 1977 and by 26.5% from 1977 to 2012.Therefore,the Qiyi Glacier's movement velocity varied greatly over the earlier 20 years(1958–1977),but presented a small decreasing trend during the latter 30 years(1977–2012).By comparing the movement velocity variation of these typical glaciers,we determined that the extent of variation was consistent among large glaciers(such as Laohugou Glacier No.12) and small glaciers(such as the Qiyi Glacier and Yanglonghe Glacier No.5),despite their different sizes.  相似文献   

海冰对南极磷虾（Euphausua superba）资源丰度的影响          下载免费PDF全文

陈峰  陈新军  刘必林  朱国平  许柳雄 《海洋与湖沼》2011,42(4):495-499

利用1997-2008年南极磷虾产量及各月南极海冰面积数据,分析南极磷虾产量的时空分布,以及海冰对南极磷虾资源丰度的影响。结果表明,近年来南极磷虾年平均产量在11万t左右,主要来自48渔区,渔汛期为3—7月。但不同渔区（48．1区、48．2区和48．3区）在不同年份和季节,其产量和CPUE均有明显差异。分析认为,48区...  相似文献