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2008年5月12日,四川汶川发生了8.0级特大地震,这是新中国成立以来破坏性最强、波及范围最广、诱发地质灾害最严重的一次强烈地震。此次地震震撼了整个中国,引起了全世界的关注。在距离震中约250km,坐落于背后山古滑坡体前缘堆积体之上的汉源老县城,出现了比周边地区高出两度的烈度异常现象。如此高的烈度异常现象引起了广大科研人员和政府相关部门的高度关注。为了科学合理地解释汉源老县城高烈度异常的原因是否与背后山滑坡有关,并进一步探讨地震作用下边坡的稳定性及动力响应等问题,本文对背后山滑坡开展了与地震相关的一系列研究。本文的研究对推动这一领域的研究工作具有重要的理论和工程意义。本文系统地归纳、总结和评述了边坡稳定性的研究进展,对背后山滑坡的工程地质条件进行了详细的调查,整理和分析了汶川特大地震背后山滑坡科学考察的全部资料。在此基础上,通过有限元数值模拟,对背后山滑坡的共振特性,静、动力稳定性以及动力响应等进行了计算和分析研究,得到了若干有意义的结论,主要研究成果如下:(1)对汉源县的震害及背后山古滑坡进行了科学考察。在汶川特大地震发生后,防灾科技学院科考组在中国地震局的统一指挥下,负责汉源和北川的科考工作,对汉源县城背后山滑坡进行了野外调查,获得了地形地貌、地层岩性、地质构造等详细资料,揭示了背后山有古滑坡存在,圈定了古滑坡的边界范围,明确了古滑坡的活动期次、特征及现今稳定性状况。调查分析结果显示,汉源老县城位于背后山古滑坡体的前缘,但并未发现古滑坡整体复活的迹象,只在坡体后部出现了几条张性裂缝。(2)建立了背后山滑坡的地质模型、力学模型和有限元计算模型。选取典型的地质剖面,建立滑坡的地质模型、力学模型和计算模型,并制定了计算方案。提出4种安全系数的计算方法,对背后山滑坡的静力稳定性进行了计算和分析,得到静力安全系数为4.09。结果表明,在静力条件下,背后山滑坡是稳定的,同时为滑坡的地震稳定性分析提供了初始的静应力场。(3)分析了背后山滑坡的共振特性。分别通过ANSYS有限元模态分析和谐响应分析,得到了边坡体固有频率和振型,以及位移与频率的关系(共振曲线)。对比分析汉源县附近强震台站记录到的地震动卓越周期,我们发现,滑坡的固有周期与其基本相近。现场考察发现,汉源老县城坐落于背后山滑坡体前缘之上,由此分析认为,可能是由于滑坡体发生共振而导致了汶川地震时汉源老县城的高烈度异常。(4)计算和分析了背后山滑坡的地震稳定性。分别用拟静力法和有限元动力时程分析法计算了地震作用下滑坡的安全系数,重点是运用后一种方法进行计算、分析和评价。通过有限元动力时程分析,得到滑坡在地震作用下的安全系数时程曲线,通过分析给出了滑坡最小动力安全系数值为1.1,由此判断,滑坡整体是稳定的。对于边坡稳定性评价,本文提出可以根据安全系数最小值是否大于1,边坡关键点速度时程末段是否趋于零,以及在地震动时程末段位移、应力矢量场大小几个方面来判断滑坡的稳定性。在判断滑坡整体稳定的情况下,针对坡肩、坡脚等关键部位,提出从受力情况和振动速度两方面对其进行局部稳定性的分析和判断,并计算了关键点处的安全系数。计算和分析的结果表明,汶川地震中汉源县高烈度异常现象与滑坡滑动无关,但在坡肩附近以及坡体上部小范围内有轻度的拉张开裂,这与实际调查现象基本符合。(5)分析和讨论了背后山滑坡的动力响应,以及地震动三要素对边坡动力响应的影响。具体计算分析中,本文在坡面上、滑体内、滑面上、坡体内设置了32个监测点进行计算和分析。计算结果发现:在坡面附近,动力响应加速度峰值相较于输入地震动加速度峰值达到3倍以上,即PGA放大系数达到3以上。并且边坡体各点PGA放大系数在竖向上随高程增加而增大;沿坡体坡面方向从左至右,PGA放大系数逐渐增大后缓慢减小。坡体水平位移在竖向上随高程增加而增大;沿坡体坡面方向从左至右,位移逐渐减小。坡面陡坎对加速度、位移响应的突变效应很明显。分析地震动三要素对坡体动力响应的影响可以看出,加速度、位移动力响应的绝对量随输入地震波振幅增大呈明显的线性增长关系,但位移、加速度放大系数保持不变,它们不受振幅的影响,只取决于岩土体材料以及频谱特性。随着输入地震波频率的增大,坡面上各点的PGA放大系数减小,位移峰值随输入地震波频率的增大而减小。持时对坡体加速度峰值响应的影响不明显。综上所述,本文在背后山古滑坡工程地质条件调查的基础上,建立了地质模型、力学模型和计算模型。采用有限单元法对背后山滑坡进行静、动力稳定性分析、共振特性分析、动力响应分析等方面的研究是可行并且有效的。本文研究结果表明,背后山滑坡在汶川特大地震中并没有发生整体滑动,只是在坡肩附近小范围内产生轻微的拉张开裂。汉源县老县城高两度的烈度异常现象与背后山滑坡整体稳定性无关,与滑坡体共振产生剧烈振动有关,坡面的加速度放大效应非常明显。此外,本文认为,对于避免地震作用下边坡的失稳问题,可以通过分析边坡响应变化趋势、响应最明显的位置以及产生共振反应的频率段等相关特征给出相应的抗震措施。 相似文献
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汶川特大地震汉源烈度异常原因的初步分析 总被引：7，自引：1，他引：6
远离震中的汉源县老县城在汶川大地震中遭到了严重震害,是Ⅵ度区内的唯一的Ⅷ度烈度异常区.汉源的地震烈度异常现象引起学术界的广泛关注.在汉源科学考察基础上,介绍了汉源震害情况,收集和整理了汉源县城及附近有关工程场地的强震和土体力学参数资料.通过背后山滑坡体有限元分析结果与汉源附近强震台记录的比较,从传递函数角度分析了背后山滑坡复活对烈度异常的影响,研究了汉源特殊土层结构对地震动的影响.结果表明,背后山滑坡的复活和特殊土层结构的放大作用等场地条件的影响是引起烈度异常的主要原因.所得结论对进一步分析汉源烈度异常的原因具有一定的参考价值. 相似文献
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汶川MS8.0大地震在远离震中近200 km的汉源县县城产生了高烈度异常, 其原因比较复杂．为了分析土层结构对汶川大地震中汉源县老县城高烈度异常的影响, 在汉源县城震害科学考察基础上, 依据地震烈度异常的分布情况, 在背后山滑坡前缘地带布设5个工程地质勘察钻孔, 获得了汉源县老县城场地土层结构资料．在现场测试和室内试验的基础上, 给出了汉源县老县城场地各层土体动力学参数．本文利用汶川地震九襄强震台的强震记录, 结合其台站的场地资料反演给出了汉源县老县城的基岩地震动时程, 作为地震反应分析的基岩输入地震动．在此基础上利用土层地震反应一维等效线性方法对汉源县老县城场地进行了地震反应分析, 并将计算所得结果与Ⅵ度区其它强震台站获得的强震记录进行比较．研究结果表明, 汉源县老县城土层结构对地震动的放大作用导致地表地震动异常, 是汉源县老县城高烈度异常的主要原因之一． 相似文献
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合理的地震动输入是定量解释震害和烈度异常的基础.以汉源老县城震害为评价基准,确定了汉源老县城高烈度异常区的汶川地震基岩地震动输入.基于汉源老县城周边的九襄、清溪、宜东和乌斯河4个强震台站记录,采用LSSRLI-1程序反演给出了各自台站的水平向基岩地震动;选取汉源县城典型场地,利用LSSRLI-1程序计算给出了不同强震台站基岩地震动作用下的场地地表加速度时程和反应谱,以最可能引起汉源老县城震害的强震台站基岩地震动作为汉源县城的基岩地震动输入.研究结果表明:九襄台站反演的基岩地震动最可能反映汶川地震时汉源老县城的基岩地震动特性,因而用九襄台站的基岩地震动作为汉源老县城的地震动输入解释汉源县城高烈度异常现象是合理的.本文的研究思路为定量解释震害的地震动输入确定提供了重要参考. 相似文献
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汶川地震中一个特殊场地研究初探 总被引：1，自引：0，他引：1
为探明汶川大地震中汉源县城高烈度异常的原因,对汉源县城震害进行了科学考察。依据震害情况,首先考察了汉源县城的建筑结构破坏,在此基础上圈定了严重破坏范围,然后考察了几处液化现象,最后对背后山滑坡进行了考察,并作了简要分析。根据汉源县城震害科学考察的结果,对汉源县城5个场点进行了对比性的地脉动测试。测试结果表明,震害严重的汉源二中、老财政局和汽车站3个场地的自振频率较小,而震害较轻的流沙河左岸和萝卜岗2个场地的自振频率较大。初步揭示了汉源县城高烈度异常的可能原因是砂土液化、滑坡和场地软弱。 相似文献
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汉源县城位于汶川M_S8.0特大地震六度区内唯一的八度异常区,为典型且罕见的远震高烈度异常区.汉源县城处于流沙河的河流阶地之上,河谷地形对地震震害有显著的影响.为定量分析河谷地形对汶川大地震汉源县高烈度异常的影响,基于汉源县城震害科学考察和场地勘察获取的资料,根据震害分布特征和流沙河谷地形的特点,选取1条实测得到的横切汉源县城并垂直流沙河河谷方向的典型剖面作为计算模型,以脉冲作为基底输入,采用有限差分方法研究了该剖面的场地放大效应,分析了地形对高烈度异常的影响.计算结果表明:汉源县城场地对地震动放大效应的显著频段是1.0~10Hz,且这一频段老县城场地的放大效应比新县城场地显著;汉源老县城场地对汶川M_S8.0地震主震的地震动有显著的放大效应,地表峰值加速度大大超过了抗震设计规范的规定值;汉源场地地形放大效应显著频段与汶川M_S8.0地震的能量集中频段基本吻合,汉源老县城建筑物的自振频率恰恰位于该频段,产生共振效应,从而造成更显著的放大效应,这也是汉源震害异常的主要原因之一.由此可见,河谷地形对地表地震动有重要的影响,在工程选址和抗震设计时应考虑其影响. 相似文献
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四川省叠溪区域地质构造复杂、地震频发,沿岷江发育有大量古(老)滑坡及堵江灾害,特别是晚更新世晚期发生了一次大型滑坡堵江事件,形成了流域内规模最大的古堰塞湖—叠溪古堰塞湖,受到国内外学者的广泛关注.本文结合野外详细调查、无人机及LiDAR测绘、地貌分析、地球物探等多种技术手段,从"空—陆—地"三个视角剖析叠溪古滑坡,揭示古滑坡的地质、地貌和堆积体内部结构特征,确定了叠溪古滑坡的位置与规模,并讨论了其对区域地质环境的长期影响效应.研究结果表明,叠溪古滑坡为一巨型顺层岩质滑坡,源于岷江左岸的高陡岩壁,滑坡体方量达到1400～2000×106 m3.位于岷江右岸的平台上可见特殊的洼地凹陷,结合密度电阻率法对坡体内部结构的反演结果,发现叠溪古滑坡坝不仅完全堵塞岷江主河道,同时还阻碍了支沟流域,形成了沿汇流方向的低电阻率通道.叠溪古滑坡坝存活了约1.5万年,随后逐渐溃决,反映了构造活跃山区滑坡堵江链式灾害对山区地貌演化的长期作用. 相似文献
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定量研究地震滑坡物质河流卸载时间对理解地震与造山带地貌演化之间的关系有着十分重要的意义.本文以青藏高原东缘龙门山构造带内岷江流域为例,定量估算了2008年汶川大地震滑坡物质的河流卸载时间.研究结果表明,如果以位于龙门山构造带内的岷江河段现有搬运能力计算,并且岷江可以有效地搬运汶川地震滑坡物质,地震滑坡物质至少在3100 yr内被岷江卸载出龙门山.而龙门山构造带中段类似2008年汶川Ms8.0级大地震的复发周期约为3000 yr左右,暗示大地震所产生的滑坡物质量可以在大地震复发周期内基本上被侵蚀和剥蚀所平衡,并被卸载出龙门山构造带. 因此,我们推断:除了周期性大地震造成的地表抬升的累积外,龙门山地区地震及其它地表过程所产生的剥蚀物质通过河流快速卸载驱动了地壳均衡反弹和深部物质上涌,形成了青藏高原东缘的高陡地形梯度带. 相关的地球物理证据表明在青藏高原东缘可能存在由地表快速剥蚀(或侵蚀)所引发的地球深部地幔软流圈物质上涌. 相似文献
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本文简要报导华北地区几个古地震实例:1.内蒙磴口西北地震毁坏的汉代古城废墟;2.宁夏平罗西北红果子沟长城错开及古地震断层陡坎;3.宁夏中宁古城子古地震断层及沙基液化变形;4.天水—宝鸡—常兴古地震黄土滑坡带;5.辽宁海城黑音寺山地震裂缝及岩崩;6. 山东临朐山旺湖相硅藻土层中地震引起的揉皱变形;7.江苏新沂嶂山闸古地震裂缝 相似文献
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The determination of the coefficient of viscosity of eruptive products gives useful elements to the knowledge of possible variations of composition and physical conditions of the magmas. 相似文献
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Geomagnetism and Aeronomy - The magnetic evolution of the active region of the Sun at the level of the photosphere has been studied. Magnetic synoptic maps of the 2007 Kitt Peak Observatory were... 相似文献
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Studia Geophysica et Geodaetica - 相似文献
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V. E. Pavlov T. Yu. Tolmacheva R. V. Veselovskiy A. V. Latyshev A. M. Fetisova I. V. Bigun 《Izvestiya Physics of the Solid Earth》2017,53(5):702-713
Until recently, the existing data prevented the geophysicists from accurately dating the Bysy-Yuryakh stratum, which outcrops in the middle reach of the Kotuy River, constraining the time of its formation to a wide interval from the end of the Late Cambrian to the beginning of the Silurian. The obtained paleomagnetic data unambiguously correlate the Bysy-Yuryakh stratum to the Nyaian regional stage and constrain its formation, at least a considerable part of it, by the Tremadocian. This result perfectly agrees with the data on the Bysy-Yuryakh conodonts studied in this work and yields a spectacular example of the successful application of paleomagnetic studies in solving important tasks of stratigraphy and, correspondingly, petroleum geology. Within the Bysy-Yuryakh stratum, we revealed a large normal-polarity interval corresponding to the long (>1 Ma) period when the geomagnetic reversals were absent. This result, in combination with the data for the Tremadocian and Middle–Upper Cambrian sequences of the other regions, indicates that (1) the rate of occurrence of the geomagnetic reversals on the eve of the Ordovician Moyero superchron of reversed polarity was at most one reversal per Ma; (2) the superchron does not switch on instantaneously but is preceded by a certain gradual change in the operation conditions of the dynamo mechanism which, inter alia, manifests itself by the reduction of the frequency of geomagnetic reversals with the approach of the superchron. This finding supports the views according to which a process preparing the establishment of the superchrons takes place at the core–mantle boundary. 相似文献
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Summary A simple model is proposed suitable for studying the effect of the ground layer of the atmosphere, polluted by aerosol, on the albedo. This model is founded on solving the equation of transfer of radiative energy. The numerical results are discussed, particular attention being paid to the analysis of errors due to neglecting the multiple reflection of solar radiation on the aerosol particles. A method which would also include the multiple reflection is proposed, and the conditions under which the presence of the aerosol is responsible for an increase or decrease of the solar radiation balance on the Earth's surface, are analysed. 相似文献
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Ivanka Jakubcová Věra Marvanová Miloš Pick Antonín Novotný Reviewer Z. Šimon 《Studia Geophysica et Geodaetica》1982,26(2):193-196
Summary The results of two different methods of the determination of the non-linearity of the gravimeter scale are compared; the economy is discussed as well. 相似文献
18.
Atmospheric temperature and humidity fields as well as information on other meteorological parameters are nowadays retrieved from radiance measurements recorded by operational meteorological satellites. Up to now, the inversion procedures used only take into account crude information on the topography of the Earth’s surface. However, the applied radiative transfer codes have to consider the Earth’s surface as the lower boundary of the atmospheric model and, therefore, need a more precise mean elevation and a classification of the roughness of the Earth’s surface. The influence of the topography of the Earth surface on retrieved temperature profiles is studied by using a physico-statistical inversion method. An objective analysis is made of the more precise mean elevation and derivation of roughness parameters using a new high-resolution digital elevation model (DEM) with a resolution of 500 m×500 m. By means of a geomorphological process and a newly developed topography rejection test, areas with a high surface roughness are localized and singled out. The influence of topography on the retrieved temperature profiles is illustrated by case studies. Changes are found predominantly in areas with a high variation of topography. Using the new high-resolution DEM and the topography rejection test, the geographical position of the calculated temperature profiles tends to be shifted towards areas with a small vertical variation of topography. The mean elevation determined by the new elevation model better characterizes the area observed. Hence, the temperature profiles can be calculated down to lower atmospheric levels. Furthermore, a guess profile better describing the atmospheric situation is selected by the more precise elevation. In addition, the temperature profiles obtained near the coast are improved considerably by the more precise determination of the surface property ‘sea’ and ‘land,’ respectively. Integration of an independent physical information such as topography leads, on average, to a slight improvement of the results of the physico-statistical inversion procedure. In some cases, however, significant improvements have been achieved regarding the desired accuracy of temperature profiles of the order of 1 K. In future, the spatial resolution of new high-resolution sounding instrumentation on the next generation of operational meteorological satellites will be increased. To exploit the resolving power of this new instrumentation, the different variation of the topography of the Earth surface, especially in regions with a high variation of topography, can be taken into account more precisely by using a high-resolution DEM. 相似文献
19.
Josef Vykutil 《Studia Geophysica et Geodaetica》1968,12(2):217-220
Резюме Дается вывод формул для вычислений длины хорды, длины и азимутов нормаляных сечений и длины геодезической линии эллипсоида.
Применяются тригонометрические функции данных величин и постоянные принятого ргфгргнц-эллипсоида, что является целесообразным
при использовании вычислителQjных машин, особенно автоматов. Рабочие формулы рекомендуются в форме (8–11).
Dedicated to Professor František Fiala on His 85th Birthday
Address: Veveři 95, Brno. 相似文献
Dedicated to Professor František Fiala on His 85th Birthday
Address: Veveři 95, Brno. 相似文献
20.
Summary The maintenance of the axisymmetric component of the flow in the atmosphere is investigated by means of a steady-state, quasi-geostrophic formulation of the meteorological equations. It is shown that the meridional variations in the time-averaged axisymmetric variables can be expressed as the sum of three contributions, one being due to the eddy heat transport, another to the eddy momentum transport, and a third to the convective-radiative equilibrium temperature which enters the problem through the specification of a Newtonian form of diabatic heating. The contributions by the large scale eddies are evaluated through the use of observed values for the eddy heat and momentum transports.The contributions from each of the three forcing mechanisms to the temperature and zonal wind fields are invstigated individually and found to be of about equal importance. The sum of the three contributions are also presented for the temperature, the zonal wind, the stream function associated with the mean meridional circulation and the corresponding vertical motion. Although the results fail to reproduce the main observed features of the lower stratosphere, they are found to be in good agreement with observations in the middle latitude troposphere. At any pressure level, for example, the computed mean zonal wind has a jet-like profile and the axis of the jet is found to slope to the south with height, as observed in the atmosphere.Based in part on a thesis submitted by the first author as partial fulfillment of the requirements for the Ph.D. degree at the University of Michigan. — Publication No. 194 from the Department of Meteorology and Oceanography, The University of Michigan. 相似文献