Characteristics of the May 12,2008 Wenchuan M_S8.0 Earthquake Sequence and Discussion on Relevant Problems

The aftershock activity of the May 12, 2008 Wenchuan Ms8.0 Earthquake Sequence shows an obvious segmented feature. Most of the large aftershocks were distributed in the north and south parts of the aftershock zone. Thrusting was dominant with a small amount of strike-slip component in the south part. The aftershock activity decayed gradually, presenting the sequence features of a mainshock-aftershock pattern. The north part was the ending area of the maiushock fracture where strike-slipping was dominant, showing an obvious swarm feature. Therefore it became the major area for large aftershocks. The modulation of the earth tide on aftershock activity is remarkable; most large aftershocks occur during the period of flood and neap tide. The time period around 16:00 was the dominant occurring time for large aftershocks. The p-value, a parameter of modified Omori formula, increases gradually with time, and reaches about 1 at the end. Based on previous study, the sequence patterns, magnitude of maximum aftershock, as well as the duration of aftershock activity has been discussed. The primary results also show that the magnitude difference between the maiushockand the maximum aftershock is proportional to the rupture size of the maiushock for huge earthquakes of about Ms8.0. This means that when the magnitudes of the earthquakes are nearly the same, large rupture size corresponds to sufficient energy release.     

RC框架结构地震倒塌易损性分析的实用方法

基于增量动力分析(IDA)的倒塌易损性分析方法是评估建筑结构抗地震倒塌能力的精细方法,但分析过程比较繁杂且非常费时。为了较快地评估建筑结构的抗地震倒塌能力,首先利用静力非线性(pushover)分析,获得结构倒塌能力的初步估计值aS*,然后将每个地面运动记录调整到aS*,对结构进行动力时程分析,记录结构的动力时程反应,利用IDA的思想得到结构的中值数倒塌谱强度?CTS。该方法与传统的增量动力分析方法相比较,可提高计算效率,计算精度也满足要求。     

北部湾5.1级强余震的短临预报

根据琼中、邕宁,广州等地磁台垂直分量日变形态“双低点”异常,地震序列缺震和地震迁移等方法,较成功地预报１９９５年３月２３日北部湾５．１级强余震。     

水库诱发地震的工程意义

本文通过对国内外２０起比较典型的水库诱发地震震例资料的分析,论述了水库诱发地震的特点和形成机制,进而说明其不可忽视的工程意义。     

A simplified fragility analysis of fan type cable stayed bridges

A simplified fragility analysis of fan type cable stayed bridges using Probabilistic Risk Analysis (PRA) procedure is presented for determining their failure probability under random ground motion. Seismic input to the bridge support is considered to be a risk consistent response spectrum which is obtained from a separate analysis. For the response analysis, the bridge deck is modeled as a beam supported on springs at different points. The stiffnesses of the springs are determined by a separate 2D static analysis of cable-tower-deck system. The analysis provides a coupled stiffness matrix for the spring system. A continuum method of analysis using dynamic stiffness is used to determine the dynamic properties of the bridges .The response of the bridge deck is obtained by the response spectrum method of analysis as applied to multidegree of freedom system which duly takes into account the quasi - static component of bridge deck vibration. The fragility analysis includes uncertainties arising due to the variation in ground motion, material property, modeling, method of analysis, ductility factor and damage concentration effect. Probability of failure of the bridge deck is determined by the First Order Second Moment (FOSM) method of reliability. A three span double plane symmetrical fan type cable stayed bridge of total span 689 m, is used as an illustrative example. The fragility curves for the bridge deck failure are obtained under a number of parametric variations. Some of the important conclusions of the study indicate that (i) not only vertical component but also the horizontal component of ground motion has considerable effect on the probability of failure; (ii) ground motion with no time lag between support excitations provides a smaller probability of failure as compared to ground motion with very large time lag between support excitation; and (iii) probability of failure may considerably increase for soft soil condition.     

1996年2月28日四川宜宾5.4级地震的参数和前兆

本文简要地给出１９９６年２月２８日四川宜宾５．４级地震的基本参数，震源机制解，余震序列及震前地震活动的特点，观测台网分布和前兆异常，以及对宜宾５．４级地震中短期预报的情况。     

2008年汶川MW7.9地震库仑应力变化的可靠性研究

基于2008年汶川M_W7.9地震精细的同震滑动分布模型,计算此次地震引起的周边地区库仑应力变化;利用变化系数(CV)评价库仑应力变化的可靠性,并评估接收断层走向、倾角、滑动角、摩擦系数、Skempton系数对库仑应力变化可靠性的影响;根据CV可靠阈值剔除不可靠库仑应力变化,分析可靠库仑应力变化与余震分布之间的关系。结果表明,库仑应力变化在正值区或负值区内部的可靠性较高,在接近正负值交界处库仑应力变化的可靠性急剧下降;接收断层倾角对库仑应力变化可靠性的影响最大;79.3%的余震位于可靠库仑应力变化分布区域,剔除不可靠库仑应力变化及不可靠库仑应力变化分布区域内余震后,余震触发率下降3.1%。     

四川芦山余震序列空间格局分析

以芦山3级以上余震数据为基础,运用GIS等方法对余震空间格局进行了研究。结果表明：1.点格局的最邻近指数为0.72,偏离随机分布,暗示余震分布具有一定聚集性：芦山、宝兴、天全是余震分布的中心区域,占总余震的87%,高震级余震也多发于此;2.距离关联维分析表明,余震在2.5~10.5km、17~22km区间内关联程度显著;32~35.5km、36~40km区间也存在关联特征,该结果与地震烈度区长短半轴、地震破裂面长度较为吻合。研究探索了余震空间点格局,对分析、判断余震特征和灾害预防具有借鉴意义。     

中国西南岩溶地区生态环境脆弱性及成因分析

岩溶环境是一种脆弱的生态环境。研究西南岩溶地区生态环境脆弱性的表现,并从水文地质环境和人类经济活动方面分析其成因。在此基础上提出西南岩溶地区生态环境问题防治对策。