A RATE-DEPENDENT ISOTROPIC DAMAGE MODEL FOR THE SEISMIC ANALYSIS OF CONCRETE DAMS

In this paper a rate-dependent isotropic damage model developed for the numerical analysis of concrete dams subjected to seismic excitation is presented. The model is shown to incorporate two features essential for seismic analysis: stiffness degradation and stiffness recovery upon load reversals and strain-rate sensitivity. The issue of mesh objectivity is addressed using the concept of the ‘characteristic length’ of the fracture zone, to show that both the softening modulus and the fluidity parameter must depend on it to provide consistent results as the computational mesh is refined. Some aspects of the numerical implementation of the model are also treated, to show that the model can be easily incorporated in any standard non-linear finite element code. The application of the proposed model to the seismic analysis of a large gravity concrete dam shows that the structural response may vary significantly in terms of the development of damage. The inclusion of rate sensitivity is able to reproduce the experimental observation that the tensile peak strength of concrete can be increased up to 50 percent for the range of strain rates that appear in a structural safety analysis of a dam subjected to severe seismic actions.     

AN INVESTIGATION INTO THE BASE SLIDING RESPONSE OF RIGID CONCRETE GRAVITY DAMS TO DYNAMIC LOADING

A series of dynamic slip tests on a concrete gravity dam model was conducted on a shaking table. The aim of the experiments was to investigate the dynamically induced sliding and overturning characteristics of a typical low height gravity dam monolith cracked at its base. Tests indicated that downstream sliding is the main instability that could be expected during an earthquake. Dynamic, finite element analyses of the experimental model, using a Lagrangian contact surface algorithm, were also performed. A comparison of the experimental and analytical responses indicated that the seismically induced slip can be predicted reasonably by such a contact surface algorithm implemented in a standard finite element package. A comparison of observed displacements with Newmark's sliding block displacements indicated that a conservative estimate of seismic induced slip of a gravity dam could be obtained by using Newmark's sliding block concept, generally adopted for earth dams and embankments.     

区域数字地震台网实时速报系统对网缘地震自动处理能力分析

为了全面评估区域数字地震台网实时速报系统对网缘地震（网内边界至边界线外100公里）的自动处理能力,我们将福建台网在2000年1月至2007年12月所编目的1074个网缘地震记录转换为模拟实时波形数据流,对系统功能进行测试与分析。测试结果表明：1.系统基本具备福建台网网缘地震的自动速报能力,速报震级下限可达ML3.0级;2.系统对86.4%福建台网网缘地震自动定位的精度小于15公里,96.2%网缘地震自动定位的精度小于30公里;3.系统对99.6%福建台网网缘地震的震级自动测定偏差不大于0.3级。以上主要结论在2008年8月21日云南盈江M5.9级地震序列的实时速报实践中得到检验。     

首都圈地区地震重力测量数据的统一处理与分析

对首都圈地区由不同施测单位用不同仪器或不同方法获得的三组重力测量数据,通过绝对和相对测量的联合平差、相对测量结果的系统差消除,建立起绝对的、统一的重力时变体系;在此基础上分析了非构造因素地壳沉降的影响,并进行了测点位移改正,消除了长波干扰;实现了绝对和相对测量方法优势互补、消除矛盾和环境干扰、扩大信息量、加密时域采样间隔等目的,提高了识别构造活动过程的能力．结果表明,两组相对测量数据之间以及其中的10期观测资料中存在系统误差,研究区东南部的非均匀性局部地壳下沉导致10个点重力值线性上升,本文用回归分析的方法进行了改正．改正后的重力时变图对1995年10月6日古冶5.0级地震有明显而完整的反映．      

地震波传播有限差分模拟的人工边界问题

在用有限差分法模拟地震波传播中，差分网格人工边界的反射问题是至关的。本文简要介绍了几种消除人工边界反射的方法及其主要优缺点，联立这些不同的吸收边界条件于实际的有限差分计算可以给出好的结果。     

离散小波变换与重力异常多重分解

小波变换多尺度分析是位场分解的有益工具.离散二维小波变换产生的低阶小波细节具有尺度不变的特征,它们不随小波变换的总阶数改变,而总阶数的增加仅增加高阶小波细节的个数和改变最后的高阶逼近.因此,用小波变换分解重力异常时,可根据地质目的来组合小波细节,从而实现有地质意义的异常分解.实验表明,用小波变换分解的重力异常小波细节,同样起到功率谱分解的作用,用分解之后的小波细节功率谱可以精确确定场源的埋深.中国大陆科学钻探场地的重力异常分解给出局部异常分解的典型例子.     

离散小波变换与重力异常多重分解

小波变换多尺度分析是位场分解的有益工具.离散二维小波变换产生的低阶小波细节具有尺度不变的特征,它们不随小波变换的总阶数改变,而总阶数的增加仅增加高阶小波细节的个数和改变最后的高阶逼近.因此,用小波变换分解重力异常时,可根据地质目的来组合小波细节,从而实现有地质意义的异常分解.实验表明,用小波变换分解的重力异常小波细节,同样起到功率谱分解的作用,用分解之后的小波细节功率谱可以精确确定场源的埋深.中国大陆科学钻探场地的重力异常分解给出局部异常分解的典型例子.     

GPS/重力边值问题的求解及应用

从分析GPS技术在确定地球形状中的作用入手，论述了建立一类新的大地边值问题——GPS/重力边值问题的意义，给出了GPS/重力边值问题的定义及数学描述，推导出GPS/重力边值问题的逼近解式，并给出了应用GPS/重力边值问题确定（似）大地水准面、地面垂线偏差及外部重力场的基本公式. 对GPS技术用于物理大地测量的优势及有待解决的问题进行了简要归纳.     

核电厂混凝土安全壳的地震可靠性分析

本文给出了自重和地震作用下核电厂混凝土安全壳的可靠性分析方法。首先基于半解析有限环元法和随机振型分析法，用首超概率给出了给定系统参数时安全壳的条件极限状态概率，然后基于此概率用推广的一次二阶矩法求解了考虑系统参数不确定性的安全壳极限状态概率。一个预应力混凝土安全壳的实例分析表明，系统参数的不确定性对安全壳的可靠性有重要影响。     

河北省沧州地区重力变化的初步分析

重力复测资料表明,沧州地区出现趋势性变化,最大变幅达92×10~(-8)m/S~2。本文的分析结果认为,这种变化部分与沧州地区地面沉降有关,部分与地壳深部的变异因素有关,不排除该地区发生中强地震的可能性。     

包头地区重力场变化与阴山带中强地震关系的初步分析

本文对包头地区的重力复测资料及重力变化、地震活动特征进行了分析，讨论了重力观测对阴山带地震监测的意义。     

体元结构模型在三维地震模型正演模拟研究中的应用

本文采用双三次康氏（Coons）曲面模拟地震界面,提出了用体元结构来表示复杂构造地区的三维地震模型,同时以此为基础建立了灵活的动态射线追踪过程,实现了快速的、更具实用性的三维地震模型的正演模拟．     

重力测量野外数据处理软件设计与应用

本文介绍了流动重力测量外业数据处理软件的开发与设计,阐述了软件的主要功能和技术要求,并介绍了软件的使用方法和野外应用效果。     

体元结构模型在三维地震模型正演模拟研究中的应用

本文采用双三次康氏（Coons）曲面模拟地震界面,提出了用体元结构来表示复杂构造地区的三维地震模型,同时以此为基础建立了灵活的动态射线追踪过程,实现了快速的、更具实用性的三维地震模型的正演模拟．     

新疆地震活动分期及活动特征的分析

本文应用公元1600年以来新疆及边邻地区6级以上强震资料，详细讨论了1882年后本区经历的地震活跃强震活动情况。指出了期中地震能量积累、大释放、剩余释放三阶段各自不同的特点；给出了划分活动期的统计模式；讨论了强震轮回的持续时间、关系、强度及存在的韵律现象；估算了本地震活跃期的大致约束时间；并对未来强震活动的发展趋势作了初步的分析。这些结果可为研究新疆地震活动性及地震形势的估计与预测问题提供线索。     

RESPONSE OF EARTH DAMS TO P AND SV WAVES USING COUPLED FE-BE FORMULATION

A study of the effects of dam–foundation interaction on the response of earth dams to obliquely incident P and SV waves is presented. Emphasis is placed on the effects of the foundation flexibility and the spatial variability of the ground motion. The study is based on a rigorous hybrid numerical formulation that combines the efficiency and versatility of the Finite Element Method (FEM) and the ability of Boundary Element Method (BEM) to account for the radiation conditions at the far field. The developed hybrid method is very powerful and can be used efficiently to obtain accurate solutions of problems of complex geometry, material heterogeneity and, for time-domain analyses, material nonlinearity. The 2-D frequency-domain formulation is used here to investigate the response of infinitely long earth dams to obliquely incident P and SV waves. By accounting rigorously for the energy radiated back into the half-space, the study demonstrates the dramatic effect of the flexibility of the foundation rock in reducing the overall response of the dam. The effects of the spatial variability of the ground motion for P and SV waves travelling across the width of the dam are also important, but somewhat less pronounced than those of the foundation flexibility.     

乌鲁木齐市近断层场地的有限元动力反应分析

根据活断层性质、倾角及上覆层厚度等因素,按照一定的比例关系,利用有限元软件建立了8个活断层场地模型,并以地震动作为输入,对这些模型进行了地震分析计算。最后对结果进行了综合对比分析,讨论了断层倾角、上覆层厚度等因素与断层破裂带之间的关系,力图从城市规划与建设的角度,对建筑物与活动断裂之间的安全距离做一探讨。     

端承桩基础轴向地震反应分析

本文对分层弹性地基中端承桩基础通过特性分析建立了合理的力学模型，通过动力分析，给出了端承桩基础轴向自振特性及在竖向地震载荷作用下强迫反应的解析解。文中的解析公式为分层弹性地基中的端承桩基础轴向动力反应分析提供了一种新的解析方法。     

COMPREHENSIVE ANALYSIS OF RECENT GRAVITY AND CRUSTAL DEFORMATION IN NORTHWESTERN GUANGXI

Northwest Guangxi is located in the Youjiang fold belt and the Hunan-Guangxi fold belt of secondary structure unit of South China fold system. The South China fold was miogeosyncline in the early Paleozoic, the Caledonian fold returned and transformed into the standard platform, and the Indosinian movement ended the Marine sedimentary history, which laid the basic structural framework of this area. Since the neotectonic period, large areas have been uplifted intermittently in the region and Quaternary denudation and planation planes and some faulted basins have been developed. Affected by the strong uplift of Yunnan-Guizhou plateau, the topography of the region subsides from northwest to southeast, with strong terrain cutting and deep valley incision. Paleozoic carbonate rocks and Mesozoic clastic rocks are mainly exposed on the earth's surface, and its geomorphology is dominated by corrosion and erosion landforms. The dating results show that most of the structures in northwest Guangxi are middle Pleistocene active faults, and the movement mode is mainly stick-slip. According to the seismogeological research results of the eastern part of the Chinese mainland, the active faults of the middle Pleistocene have the structural conditions for generating earthquakes of about magnitude 6. In the northwest Guangxi, the crustal dynamic environment and geological structure are closely related to Sichuan and Yunnan regions. Under the situation that magnitude 6 earthquakes occurred successively in Sichuan and Yunnan region and magnitude 7 earthquakes are poised to happen, the risk of moderately strong earthquakes in the northwest Guangxi region cannot be ignored. Based on the analysis of deep structure and geophysical field characteristics, it is concluded that the Tian'e-Nandan-Huanjiang area in the northwestern Guangxi is not only the area with strong variation of the Moho surface isobath, but also the M_L3.0 seismic gap since September 2015, and the abnormal low b value area along the main fault. Regions with these deep structural features often have the conditions for moderately strong earthquakes. The paper systematically analyzes the spatial and temporal distribution features and mechanism of regional gravitational field and horizontal crust movement and further studies and discusses the changes of regional gravitational field, crustal horizontal deformation and interaction between geologic structure and seismic activity based on 2014-2018 mobile gravity measurements and 2015-2017 GPS observation data in the northwestern Guangxi. The results show that:1)On July 15, 2017, a M_S4.0 earthquake in Nandan happened near the center of four quadrants of changes of gravity difference, and the center of abnormal area is located at the intersection of the Mulun-Donglang-Luolou Fault, the Hechi-Nandan Fault and the Hechi-Yizhou Fault. The dynamic graph of differential scale gravitational field reflects the gravity changes at the epicenter before and after the Nandan earthquake, which is a process of system evolution of "local gravity anomaly to abnormal four-quadrant distribution features → to earthquake occurring at the turning point of gravity gradient zone and the zero line to backward recovery variation after earthquake". Meanwhile, according to the interpretation of focal mechanism of the Nandan earthquake, seismogram and analysis of seismic survey results, the paper thinks that the four-quadrant distribution of positive and negative gravity, which is consistent with the effect of strike-slip type seismogenic fault before Nandan earthquake, demonstrates the existence of dextral strike-slip faulting; 2)The pattern of spatial distribution of gravitational field change in northwestern Guangxi is closely related to active fault. The isoline of cumulative gravity generally distributes along Nandan-Hechi Fault and Hechi-Yizhou Fault. The gravity on both sides of the fault zone is different greatly, and gradient zone has influences on a broad area; the spatial distribution of deformation field is generally featured by horizontal nonuniformity. Tian'e-Nandan-Huanjiang area is located at the high gradient zone of gravity changes and the horizontal deformation surface compressional transition zone, as well as near the intersection of Hechi-Yizhou Fault, Hechi-Nandan Fault and Du'an-Mashan Fault; 3)The geometric shape of gravitational field in northwestern Guangxi corresponds to the spatial distribution of horizontal crustal movement, which proves the exchange and dynamic action of material and energy in the region that cause the change and structural deformation of fault materials and the corresponding gravity change on earth's surface. The recent analysis of abnormal crustal deformation in northwestern Guangxi shows that Tian'e-Nandan-Huanjiang is a gradient zone of abnormal gravity change and also a horizontal deformation surface compressional transition zone. It locates at the section of significant change of Moho isobaths, the seismicity gap formed by M_L3.0 earthquakes and the abnormal low b-value zone. According to comprehensive analysis, the region has the risk of moderately strong earthquake.     

三峡水库首区重力固体潮观测资料分析

介绍了中国科学院测量与地球物理研究所的LCR-ET20重力仪和中国地震局地震研究所的DZW-9重力仪在三峡水库首区的重力固体潮比对观测.获得了该地区高精度的重力固体潮潮汐参数,估算了DZW-9重力仪的格值,其值为（-756.06plusmn;0.05）times;10-8（mbull;s-2）/v. 分析了相应仪器的重力观测残差, 数值结果表明DZW-9重力仪的长期漂移具有线性特征, 观测精度与LCR-ET20重力仪在同一量级. 本文提供的相关结果可为该地区地表和空间大地测量观测提供有效的重力潮汐改正模型.