2018年斐济M_W8.2深震:高频辐射过程和发生原因          下载免费PDF全文

张喆  许力生  杜海林 《地球物理学报》2019,62(11):4279-4289

2018年8月19日，在斐济东部海域563 km深处发生了一次M_W8.2地震.我们首先挑选位于美国阿拉斯加地区的131个宽频带台站构成台阵，选用垂直分量0.5~2 Hz的高频信号，利用广义台阵反投影技术对这次地震的破裂过程进行了成像，然后基于破裂速度对地震的辐射效率进行了估计.结果表明，这次地震总体上呈单侧破裂，破裂方位在3.0°左右，破裂总长度约51 km，持续时间22 s，平均破裂速度为2.5 km·s^-1.但能量释放有2次高峰，形成两次子事件.第一次为前10 s，峰值在7 s左右，破裂速度为2.9 km·s^-1，辐射效率为45%.第二次为10~22 s，峰值在15 s左右，破裂速度为1.6 km·s^-1，辐射效率为26%.结合震源位置、震源机制、破裂速度以及辐射效率，我们认为这次地震是由于俯冲板块前缘受到下部地幔物质上浮阻力引起的剪切失稳所致，起初板块内部的脆性破裂表现突出，致使辐射效率较高，后来震源处高温高压下的熔融耗散特征逐渐凸现，致使辐射效率下降.  相似文献   

桥梁沉井基础抗震性能研究现状及展望          下载免费PDF全文

王义  陈兴冲  张熙胤  张永亮  刘正楠 《世界地震工程》2020,(1):044-55

随着国内外大跨桥梁特别是跨海桥梁建设的迅速发展，沉井基础在桥梁基础中所占的比例越来越大。虽然沉井基础作为1种刚性基础具有良好的力学性能，然而震害实践表明沉井基础在地震作用下也并非万无一失。通过分析国内外典型桥梁沉井基础的震害特征发现，沉井基础的地震破坏与桩基础有显著差异，且与埋置深度有直接关系；研究表明:地震作用下沉井基础的破坏机理及地基承载力与静力作用下明显不同，但目前在该方面的研究还较为欠缺；总结和对比了现有几种沉井基础-土相互作用研究方法，并分析了几种研究方法的优缺点和适用场合；同时也归纳和对比了各国抗震规范对桥梁沉井基础的基本规定、适用范围、计算方法和构造规定等方面的内容。最后结合现有的研究现状对沉井基础抗震性能研究的发展方向进行了展望，此外，随着我国跨海、跨江及跨库区大跨桥梁建设的发展，地震力和波浪力等多灾害因素共同作用下深水沉井基础桥梁破坏机理及设计方法的研究势在必行。  相似文献   

Crack nucleation in saturated porous media     

Luc Dormieux  Eric Lemarchand  Thomas Carlioz  Laurent Jeannin 《国际地质力学数值与分析法杂志》2020,44(5):553-574

Crack nucleation has been the subject of important contributions in the last two last decades. However, it seems that few attention has been granted to the case of saturated porous media. This is the question addressed in the present paper which is devoted to nucleation in traction mode. From a physical point of view, nucleation is a sudden phenomenon, so that the material response is both adiabatic and undrained. In the spirit of the variational approach, the nucleated crack is viewed as the final state of a region of space in which the material undergoes a full damage process. In traction mode, the opening of a saturated crack in undrained condition induces a drop of fluid pressure. In case of low fluid compressibility, the presence of the fluid delays the brittle failure usually associated with nucleation, as long as the fluid pressure remains above the saturation vapor pressure. Nucleation is therefore possible only if a partial vaporization of the fluid takes place.  相似文献   

Three-dimensional finite element simulation of fracture propagation in rock specimens with pre-existing fissure(s) under compression and their strength analysis     

Ramin Pakzad  Shanyong Wang  Scott W. Sloan 《国际地质力学数值与分析法杂志》2020,44(10):1472-1494

A FORTRAN program, consistent with the commercially available finite element (FE) code ABAQUS, is developed based on a three-dimensional (3D) linear elastic brittle damage constitutive model with two damage criteria. To consider the heterogeneity of rock, the developed FORTRAN program is used to set the stiffness and strength properties of each element of the FE model following a Weibull distribution function. The reliability of the program is assessed against available experimental results for granite cylindrical specimens with a throughgoing, flat and inclined fissure. The calibration procedure of the material parameters is explained in detail, and it is shown that the compressive to tensile strength ratio can have a substantial influence on the failure response of the specimens. Numerical simulations are conducted for models with different levels of heterogeneity. The results show a smaller load bearing capacity for models with less homogeneity, representing gradual coalescence of fully damaged elements forming throughout the models during loading. The maximum load bearing capacity is studied for various combinations of inclination angles of two centrally aligned, throughgoing and flat fissures of equal length embedded in cylindrical models under uniaxial and multiaxial loading conditions. The key role of the compressive to tensile strength ratio is highlighted by repeating certain simulations with a lower compressive to tensile strength ratio. It is proven that the peak loads of the rock models with sufficiently small compressive to tensile strength ratios containing two throughgoing fissures of equal length are similar, provided that the minimum inclination angles of the models are the same. The results are presented and discussed with respect to the existing experimental findings in the literature, suggesting that the numerical model applied in this study can provide useful insight into the failure behaviour of rock-like materials.  相似文献   

Characteristics and Analysis of the Seismic Damage from the M_S7.0 Jiuzhaigou Earthquake in the Area between Songpan and Jiuzhaigou     

Yan Zhaolun  Peng Xiaobo  Li Shuguang  Hong Haichun 《中国地震研究》2018,32(2):173-188

This paper expounds the features of the buildings and analyzes the seismic disaster characteristics of the Jiuzhaigou M_S7. 0 earthquake in the area between Songpan and Jiuzhaigou. New buildings (especially the frame structure) had good anti-seismic performance,but brick-wood structures and brick-concrete structures sustained large amounts of damage in the earthquake. By computing the seismic damage index,we found that the seismic damage index of the frame structure was far less than that of civil structures and brick-wood structures. The seismic damage index of frame structures were all zero in the Ⅵ area,and increased rapidly with the increase of intensity,but the increasing range was reduced. We also discussed how to evaluate the intensity in areas where there was a lack of buildings or there was only one structure type,which can be referenced in future field work.  相似文献   

窑洞外形特征对结构抗震性能影响研究          下载免费PDF全文

王飞剑  刘如山  马朝晖 《地震工程学报》2018,40(5):910-918

调查发现山西北部农村地区农居窑洞多是独立式土坯窑洞,结构主要受力体系是土坯砌体砌筑拱结构,其建造无统一标准,外形样式存在差异。由于拱结构的内力分布对外形尺寸变化比较敏感,为研究窑洞外形特征对结构抗震性能影响,建立相应的有限元模型进行计算分析,对比不同外形特征窑洞在地震作用下的损伤情况,并结合历史震害,指出窑洞结构的薄弱位置。研究结果表明覆土较厚的窑洞容易损伤,连拱孔数较多窑洞的两侧位置更容易发生破坏,拱的曲线形状对结构抗震性能有一定影响,合理拱曲线窑洞的抗震性能优于一般形状窑洞。  相似文献   

Implementation of a coupled plastic damage distinct lattice spring model for dynamic crack propagation in geomaterials          下载免费PDF全文

Chao Jiang  Gao‐Feng Zhao 《国际地质力学数值与分析法杂志》2018,42(4):674-693

This paper studies dynamic crack propagation by employing the distinct lattice spring model (DLSM) and 3‐dimensional (3D) printing technique. A damage‐plasticity model was developed and implemented in a 2D DLSM. Applicability of the damage‐plasticity DLSM was verified against analytical elastic solutions and experimental results for crack propagation. As a physical analogy, dynamic fracturing tests were conducted on 3D printed specimens using the split Hopkinson pressure bar. The dynamic stress intensity factors were recorded, and crack paths were captured by a high‐speed camera. A parametric study was conducted to find the influences of the parameters on cracking behaviors, including initial and peak fracture toughness, crack speed, and crack patterns. Finally, selection of parameters for the damage‐plasticity model was determined through the comparison of numerical predictions and the experimentally observed cracking features.  相似文献   

典型砖木结构农居地震弹塑性有限元分析   总被引：1，自引：1，他引：0       下载免费PDF全文

姚新强  孙柏涛  陈宇坤  杨绪连 《地震工程学报》2018,40(1):32-40

针对我国农居结构中比例最高的砖木结构,选取典型结构运用ABAQUS有限元软件进行模态和地震时程弹塑性分析。给出M0.5和M5两种砌筑强度砖木结构农居的前三阶特征周期和振型,并与经验周期公式值进行对比分析,提出后者存在的问题和修改建议。选取天津波作为地震动时程输入,分别计算不同峰值加速度下两种砖木结构农居弹塑性地震反应,给出相应的拉损伤云图,并对结构的破坏特征进行分析,给出结构抗震薄弱部位。结果表明,砌筑强度是决定结构抗震能力的关键因素之一。  相似文献   

Satellite-based Estimates of Canopy Photosynthetic Parameters for an Alpine Meadow in Northern     

NIU Ben  HE Yongtao  ZHANG Xianzhou  SHI Peili  DU Mingyuan 《资源与生态学报(英文版)》2020,11(3):253-262

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基于类柔度差曲率和频率摄动的结构损伤识别          下载免费PDF全文

何容  谭亚可  郭琪璇  何伟 《地震工程学报》2020,42(4):825-832

为提高梁式结构损伤诊断的效率,提出一种基于类柔度差曲率和频率摄动的结构损伤识别方法。首先根据结构振动理论,研究广义柔度矩阵计算公式;再利用模态柔度对结构损伤灵敏性高的优点,改进基于柔度差曲率的损伤定位指标,定义类柔度差曲率LCFC损伤指标,并初步识别损伤;最后基于矩阵摄动进行结构损伤识别结果确认。考虑多种损伤工况,对一简支梁结构进行损伤识别数值模拟验证。结果表明:仅使用一阶模态,建立的类柔度差曲率LCFC指标对梁式结构损伤定位具有良好的诊断效果,且计算工作量小;对于含边界损伤单元的多损伤工况,当损伤程度大于10%时,LCFC指标识别有效;当损伤程度不大于25%时,各工况二阶摄动识别结果精度较高,相对误差较一阶摄动结果明显降低,证明了该方法的实用性、有效性和精确性。  相似文献