Estimation of strong seismic ground motion for engineering use in Perth Western Australia

Probabilistic seismic hazard analysis (PSHA) was performed to determine two alternate magnitude-distance combinations for the 475 yr event, and the worst-case scenario event in Perth, Western Australia. Regional strong ground motion (SGM) time histories on rock sites are used to modify an eastern North America (ENA) seismic model to suit southwest Western Australian (SWWA) conditions. This model is then used to stochastically simulate a set of 475 yr design events and a set of worst-case scenario event for rock sites in the Perth metropolitan area (PMA). The simulated time histories are then used as input to typical soft soil sites in the PMA to estimate surface ground motions. The spectral accelerations of the ground motions on rock and soil sites are calculated and compared with the corresponding design spectra defined in current and previous Australian earthquake loading code. Discussions of the adequacy of the code spectra and the differences to ours, along with implications on structural response and damage are made.     

Influence of plasticity on the seismic soil–micropiles–structure interaction

This paper includes an analysis of the influence of soil plasticity on the seismic response of micropiles. Analysis is carried out using a global three-dimensional modeling in the time domain. The soil behavior is described using the non-associated Mohr–Coulomb criterion. Both the micropiles and the superstructure are modeled as three-dimensional beam elements. Proper boundary conditions are used to ensure waves transmission through the lateral boundaries of the soil mass. Analyses are first conducted for harmonic loadings and then for real earthquake records. They show that plasticity could have a significant influence on the seismic response of the soil–micropiles–structure systems. This influence depends on the amplitude of the seismic loading and the dominant frequencies of both the input motion and the soil–piles–structure system.     

Travel distance of failed slopes during 2004 Chuetsu earthquake and its evaluation in terms of energy

A number of slope failures during the 2004 Niigataken Chuetsu earthquake were investigated, revealing that the travel distance becomes longer as the slope gets gentler and the failed soil mass gets larger. An energy-based approach, proposed in previous research to evaluate the travel distance of failed slopes, is modified by adding the model test results and introducing a simple evaluation method. The energy approach is then applied to a number of slopes failed during the earthquake to back-calculate mobilized friction coefficients, revealing their strong dependency on initial slope inclinations. The friction coefficient was found to be smaller than the initial slope inclination for gentler slopes, indicating that the failed soil mass tends to accelerate. In contrast, that for steeper slopes was higher than initial slope inclination. The friction coefficient was found to decrease with increasing volume of failed slope, which is quite consistent with previous case studies including large non-seismic landslides.     

A new definition of strong motion duration and related parameters affecting the response of medium–long period structures

This study presents a new definition of the strong motion duration combining the alternative bracketed and significant duration definitions. Based on the time integral of the absolute ground velocity, a new index is defined, as cumulative absolute displacement (CAD), and used to estimate the strong motion duration. The proposed bracketed-significant duration t_bs is found to be well correlated with the strong motion part of the records, especially in the case of near-source events. The duration t_bs and the CAD index are used to assess the anticipated structural behavior of medium–long period structures.     

Numerical modelling of the transverse dynamic behaviour of circular tunnels in clayey soils

In this paper, different approaches aimed at investigating the dynamic behaviour of circular tunnels in the transverse direction are presented. The analysed cases refer to a shallow tunnel built in two different clayey deposits. The adopted approaches include 1D numerical analyses performed modelling the soil as a single-phase visco-elastic non-linear medium, the results of which are then used to evaluate the input data for selected analytical solutions proposed in the literature (uncoupled approach), and 2D fully coupled FE simulations adopting visco-elastic and visco-elasto-plastic effective stress models for the soil (coupled approach). The results are proposed in terms of seismic-induced loads in the transverse direction of the tunnel lining. The different constitutive hypotheses adopted in the coupled numerical approach prove to play a significant role on the results. In particular, the plasticity-based analyses indicate that a seismic event can produce a substantial modification of loads acting in the lining, leading to permanent increments of both hoop force and bending moment.     

Classification of seismic signals at Villarrica volcano (Chile) using neural networks and genetic algorithms

Each volcano has its own unique seismic activity. The aim of this work is to construct a system able to classify seismic signals for the Villarrica volcano, one of the most active volcanoes in South America. Since seismic signals are the result of particular processes inside the volcano's structure, they can be used to forecast volcanic activity. This paper describes the different kinds of seismic signals recorded at the Villarrica volcano and their significance. Three kind of signals were considered as most representative of this volcano's activity: the long-period, the tremor, and the energetic tremor signals. A classifier is implemented to read the seismic registers at 30-second intervals, extract the most relevant features of each interval, and classify them into one of the three kinds of signals considered as most representative of this particular volcano. To do so, 1033 different kinds of 30-s signals were extracted and classified by a human expert. A feature extraction process was applied to obtain the main characteristics of each of them. This process was developed using criteria which have been shown by others to effectively classify seismic signals, based on the experience of a human expert. The classifier was implemented with a Multi-Layer Perceptron (MLP) artificial neural network whose architecture and training process were optimized by means of a genetic algorithm. This technique searched for the most adequate MLP configuration to improve the classification performance, optimizing the number of hidden neurons, the transfer functions of the neurons, and the training algorithm. The optimization process also performed a feature selection to reduce the number of signal features, optimizing the number of network inputs. The results show that the optimized classifier reaches more than 93% exactitude. identifying the signals of each kind. The amplitude of the signals is the most important feature for its classification, followed by its frequency content. The described methodology can be used to classify more seismic signals to improve the study of the activity of this volcano or to extend the study to other active volcanoes of the region.     

非对称大底盘双塔连体结构的动力特性和地震响应分析

依据现行抗震设计规范,运用三维有限元软件ANSYS对某25层大底盘非对称双塔连体结构进行了时程法地震反应分析,得到结构的自振特性和地震响应,并与未设连体的双塔结构的结果进行了比较.结果表明增设连体后双塔的扭转振型更加丰富,且运动和变形得到了统一和协调.     

对新疆乌恰—喀什地区年度地震预测的总结与思考

在对新疆1973年以来年度地震预测情况进行综合研究基础上,重点分析了乌恰-喀什周围地区年度预测的阶段性特点,并对这一地区1900年以来M≥6地震和1972-2008年M≥5.5地震活动特征进行了的研究.认为对该区域地震活动规律性特点认识不足,没有遵循本地区地震活动的基本规律对地震趋势进行客观判断,是造成地震危险区预测效果较差的主要原因.依据地震活跃与间歇的特点认为2008年底开始乌恰-喀什周围地区将进入一个新的活跃时段,这一地区可能仍将继续被划定为年度强地震危险区.     

九江—瑞昌序列震源位置及震源区速度结构的联合反演

采用震源位置和速度结构的联合反演方法确定2005年九江一瑞昌5.7级地震序列的分布和震源区的速度结构.结果显示九江一瑞昌地震序列存在NW330.方向和NE550方向的两组共轭分布,其中NW330.方向的优势分布更为明显;震源深度分布在3～18km的范围.地震主体破裂发生在上地壳-中地壳过渡层的P波速度低速区内,主震发生后余震向东南与西北方向两头扩展,其中往西北方向破裂时可能遇到了障碍体,积累的能量转向西南-北东方向继续破裂,引发了4.8级强余震.     

广东数字地震台网‘十五’系统的几种地震定位方法的定位效果分析

选取广东省‘十五’数字地震台网2007年6-9月试运行以来记录到的32次地震事件,运用地震台网地震速报及地震编目使用的几种常规地震定位软件,并将其结果与‘九五’编目产出的结果进行了比较,结果表明：对于网内地震。单纯型定位法及HYP02000程序的定位法结果稍优于Hyposat定位法：对于网缘地震,3种定位程序得到的结果相差不大。