滑行波震相对珠江口地区壳内低速层的约束作用     

杨碧峰  熊成  曹敬贺  孙金龙  万奎元  夏少红 《热带海洋学报》2020,39(1):106-119

深入研究珠江口地区海陆过渡带壳内低速层的结构和构造特征对于理解板内地震的发震机理、孕震构造及该区域的地壳结构具有重要的地质地球物理意义。利用2015年珠江口区域海陆地震联测L2-ME测线上的19个地震台站(包括陆上台站14台, 海底地震仪5台)记录到的地震数据来探明该区域低速层的结构和构造特征。在常规震相的基础上, 加入了大量的滑行波震相(Ph)进行结构模型计算, Ph震相的增加使得地壳内部10~20km范围内的射线覆盖密度有了显著提高, 从而获得了L2-ME测线下方更为精确的地壳纵波速度结构模型。结果发现, 模型中测线下方13~18km深度范围内稳定连续展布的壳内低速层被清晰成像, 其内部速度稳定在5.7~6.0 km·s^-1之间, 与上下层界面速度差分别为0.5km·s^-1、0.4km·s^-1, 低速特征明显。该低速层厚度由陆侧的3.5km左右降至海侧的1km, 呈现出向海侧逐渐减薄的趋势, 低速层底界面起伏变化较大且具有与莫霍面相似的起伏特征。  相似文献   

滑移隔震结构的抗风稳定性分析   总被引：1，自引：0，他引：1  

李黎  樊爱武  胡亮  张行 《世界地震工程》2007,23(4):148-152

滑移隔震结构要求在风荷载作用下保持安定。应用多种方法研究了不同摩擦系数、不同基本风压作用下滑移隔震体系的抗风稳定性：（1）考虑一阶振型的等效静力法；（2）采用谐波合成法模拟近似的具有给定功率谱密度函数的脉动风，作用于结构上，进行动力时程分析；（3）根据风压的功率谱密度函数计算脉动风压的概率法。研究结果表明时程分析法与概率法得到的风荷载相近，大于等效静力法得到的风荷载。摩擦系数为0.1可以满足基本风压小于0.90kN／m^2地区滑移隔震结构的抗风稳定性。  相似文献   

Seismic response control of smart sliding isolated buildings using variable stiffness systems: an experimental and numerical study     

Satish Nagarajaiah  Sanjay Sahasrabudhe 《地震工程与结构动力学》2006,35(2):177-197

Effectiveness of a new semiactive independently variable stiffness (SAIVS) device in reducing seismic response of sliding base isolated buildings is evaluated analytically and experimentally. Through analytical and experimental study of force—displacement behaviour of the SAIVS device, it is shown that the device can vary stiffness continuously and smoothly between minimum and maximum stiffness. Passive sliding base isolation systems reduce interstorey drifts and superstructure accelerations, but with increased base displacements, which is undesirable, under large velocity near fault pulse type earthquakes. It is a common practice to incorporate non‐linear passive dampers into the isolation system to reduce bearing displacements. Incorporation of passive dampers, however, may result in increased superstructure accelerations and drifts; while, properly designed passive dampers can be beneficial. A viable alternative is to use semiactive variable stiffness systems, which can vary the period of the sliding base isolated buildings in real time, to simultaneously reduce bearing displacements and superstructure responses further than the passive systems, which deserves investigation. This study investigates the performance of a 1:5 scaled smart sliding base isolated building model equipped with the SAIVS device analytically and experimentally, under near fault earthquakes, by developing a new moving average non‐linear tangential stiffness control algorithm for control of the SAIVS device. The SAIVS device reduces bearing displacements further than the passive cases, while maintaining isolation level forces and superstructure responses at the same level as the passive minimum stiffness case, indicating the significant potential of the SAIVS system. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Response of structures supported on SCF isolation systems     

M. Hamidi  M. H. El Naggar  A. Vafai 《地震工程与结构动力学》2003,32(10):1555-1584

Aseismic base isolation is an effective method used to protect structures and their contents against earthquakes. An isolated structure may be designed to remain elastic throughout major ground motions as a result of the efficiency of the isolation systems. In this paper, the equations of motion of two‐dimensional elastic structures supported on a new base isolation system called the Sliding Concave Foundation (SCF) are presented and a procedure for their solution is suggested. The responses of a number of structures subjected to different earthquake records are evaluated and the results are compared with those of the same structures supported on two other famous isolation systems and also a fixed base condition. The results indicate the effectiveness of the SCF in protecting the supported structures even during very strong and/or long period earthquakes. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

黄河黑山峡大柳树坝址岩体滑移-弯曲拉裂松动的有限元分析     

周立新  米素婷  黄晓波 《地球物理学进展》2003,18(3):426-428

通过实地勘测研究，建立了黄河黑山峡大柳树坝址区岩体的滑移-弯曲拉裂松动变形模式。并运用2D-Sig-ma有限元程序对其进行分析，充分论证了坝址区岩体的顺层滑移-弯曲拉裂是该处岩体松动的一种重要模式，并给出了若干重要结论。  相似文献   

考虑强度退化效应的堤坝抗震稳定性评价方法   总被引：2，自引：2，他引：2  

李湛  栾茂田 《岩土力学》2004,25(Z2):409-413

考虑土的动强度随振动孔隙压力上升的衰减效应,将拟静力极限平衡分析和滑动体位移分析相结合,提出了堤坝抗震稳定性评价方法.首先,基于土工动力有限元分析,确定坝坡潜在滑动土体的平均加速度时程,进而,基于拟静力概念,采用极限平衡分析,确定坝坡的安全系数随时间的变化历程,其中当安全系数瞬时小于1时,表明坝坡在地震中处于瞬时超载状态,采用Newmark刚体滑块模型估算瞬时超载所产生的滑动位移,将各个超载阶段的滑动位移叠加,求得设计地震动作用下堤坝边坡的累积滑移量,根据这种方法所进行的数值计算与分析表明,考虑强度循环退化效应后所得到的坝坡滑移量更为合理.  相似文献   

运用滑移线理论确定挤扩多盘桩盘下土体应力计算模式     

钱永梅  尹新生  蒋荣庆  王若竹 《吉林大学学报(地球科学版)》2004,(Z1)

通过对挤扩多盘桩桩周土体极限破坏机理的理论分析及试验研究,证明盘下土体的破坏形式为滑移破坏。据此,应用Coulumb-Mohr定律建立了应力函数表达式,并运用滑移线理论,通过简单破坏区域,选择适合盘下土体的破坏形式Prandtl区域应力场,建立极坐标应力方程,从而推导出挤扩多盘桩盘下土体应力的计算模式,以便进一步确定土体极限承载力。  相似文献   

Formation of clastogenic lava flows during fissure eruption and scoria cone collapse: the 1986 eruption of Izu-Oshima Volcano, eastern Japan     

Janet M. Sumner 《Bulletin of Volcanology》1998,60(3):195-212

The 1986 eruption of B fissure at Izu-Oshima Volcano, Japan, produced, among other products, one andesite and two basaltic andesite lava flows. Locally the three flows resemble vent-effused holocrystalline blocky or aa lava; however, remnant clast outlines can be identified at most localities, indicating that the flows were spatter fed or clastogenic. The basaltic andesite flows are interpreted to have formed by two main processes: (a) reconstitution of fountain-generated spatter around vent areas by syn-depositional agglutination and coalescence, followed by extensional non-particulate flow, and (b) syn-eruptive collapse of a rapidly built spatter and scoria cone by rotational slip and extensional sliding. These processes produced two morphologically distinct lobes in both flows by: (a) earlier non-particulate flow of agglutinate and coalesced spatter, which formed a thin lobe of rubbly aa lava (ca. 5 m thick) with characteristic open extension cracks revealing a homogeneous, holocrystalline interior, and (b) later scoria-cone collapse, which created a larger lobe of irregular thickness (<20 m) made of large detached blocks of scoria cone interpreted to have been rafted along on a flow of coalesced spatter. The source regions of these lava flows are characterized by horseshoe-shaped scarps (<30 m high), with meso-blocks (ca. 30 m in diameter) of bedded scoria at the base. One lava flow has a secondary lateral collapse zone with lower (ca. 7 m) scarps. Backward-tilted meso-blocks are interpreted to be the product of rotational slip, and forward-tilted blocks the result of simple toppling. Squeeze-ups of coalesced spatter along the leading edge of the meso-blocks indicate that coalescence occurred in the basal part of the scoria cone. This low-viscosity, coalesced spatter acted as a lubricating layer along which basal failure of the scoria cone occurred. Rotational sliding gave way to extensional translational sliding as the slide mass spread out onto the present caldera floor. Squeeze-ups concentrated at the distal margin indicate that the extensional regime changed to one of compression, probably as a result of cooling of the flow front. Sliding material piled up behind the slowing flow front, and coalesced spatter was squeezed up from the interior of the flow through fractures and between rafted blocks. The andesite flow, although morphologically similar to the other two flows, has a slightly different chemical composition which corresponds to the earliest stage of the eruption. It is a much smaller lava flow emitted from the base of the scoria cone 2 days after the eruption had ceased. This lava is interpreted to have been formed by post-depositional coalescence of spatter under the influence of the in-situ cooling rate and load pressure of the deposit. Extrusion occurred through the lower part of the scoria cone, and subsequent non-particulate flow of coalesced material produced a blocky and aa lava flow. The mechanisms of formation of the lava flows described may be more common during explosive eruptions of mafic magma than previously envisaged. Received: 30 May 1997 / Accepted: 19 May 1998  相似文献   

Determination of Characteristics of Main Sliding Lithological Groups with Displacement Table of Pascal-Yanghui Triangle in China     

Yan Tongzhen Li Yun ’an Faculty of Environmental Science  Geotechnique  China University of Geosciences  Wuhan Zhong Yufang Faculty of Earth Sciences  China University of Geosciences  Wuhan 《中国地质大学学报(英文版)》1998,9(2)

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广义纵弯褶皱叠加机制、类型及其应用   总被引：1，自引：0，他引：1  

杜思清  魏显贵  刘援朝 《矿物岩石》1998,(Z1)

早期褶皱的迁移机制和迁移型叠加类型的发现扩大了对广义纵弯褶皱叠加机制和类型的认识。广义叠加机制有多种,其中包括迁移和位移,褶皱变缓和展平,岩层变陡和变缓等。广义叠加类型中除基本类型外还有限制型、展平残留型、叠加挠曲、共轴重褶等。本文将用几个地质实例予以说明。此外还将讨论叠加褶皱层应变和小构造的多成因和应用问题,其中包括斜纵弯应变和褶皱变缓展平引起的应变和小构造。  相似文献