断层倾角对上/下盘效应的影响

上／下盘效应是近断层地震动的显著特征之一。上／下盘效应的影响因素很多,由于靠近断层,与震源相关的因素成为主导因素,尤其是断层倾角的影响最为明显。本文采用二维有限元数值模拟的方法模拟了近断层地震动,定量地考查了断层倾角对上／下盘效应的影响。结果表明：无论是走滑型断层还是倾滑型断层,随着断层倾角从0°～90°的增大过程中,上／下盘效应先迅速增大然后缓慢减小。     

近断层地震动的上/下盘效应研究

近断层地震动由于其自身不同于远场地震动的特征以及对工程结构产生的严重破坏,成为近年来工程地震界的研究热点。近断层地震动的影响因素众多,除常规的震源、路径以及场地条件之外,上/下盘效应和破裂方向性效应的影响较为突出,两者对近断层地震动的峰     

芦山地震地震动上下盘效应研究

2013年4月20日的芦山7.0级地震是继2008年5月12日汶川8.0级特大地震之后,发生在龙门山断裂带上的又一次大震级逆冲型地震.与汶川地震相比,芦山地震的发震断层没有地表出露,断层的滑动角更大,其逆冲性质更强烈.本文挑选了芦山地震中断层距小于200km的45条强震动记录,基于地震动衰减关系进行统计分析,对比了上盘和下盘台站地震动参数相对于衰减关系的对数残差.结果表明：芦山地震的上下盘效应明显,近断层上盘地震动的高频成分要高于同断层距的下盘;上盘地震动衰减要明显快于下盘.地震动衰减关系用简单的一个距离参数很难描述近场断层尺寸效应的影响,也很难模拟地震动上下盘效应.因此,在近场强地面运动模拟中,应多考虑有限断层模型,以模拟断层的尺寸效应.     

基于逆断层动力学模型的三维山体地震动谱元法模拟

逆冲断层是常见的断层错动形式,具有释放地震能量大破坏力强的特征,同时大量震害调查和强震观测表明,山体地形对地震动的显著放大效应会进一步加重震害,然而目前还鲜有针对逆冲断层作用下山体地震动模拟的研究.文中即采用谱元法,建立含动力学逆断层震源和三维山体地形的整体物理模型,研究了动力学逆断层地震作用下的三维山体动力响应.文中...     

复杂场地条件下震源参数对断层附近长周期地震动的影响

基于显式有限元方法和运动学震源模型并利用昆明盆地三维地下构造模型,本文研究了震源参数对断层附近长周期地震动的影响.结果表明,断层的破裂方式、埋藏深度、破裂速度以及断层面上位错的不均匀分布对断层附近长周期地震动有重要影响.不同破裂方式下,破裂的方向性强的区域分布不同,由于破裂的方向性效应和复杂场地条件的共同作用,导致不同破裂方式的断层附近地震动分布差别很大.随着破裂速度的增加,方向性效应更加明显,断层附近的长周期地震动也随之增大;对于浅源地震,随着断层埋深的增加,地震动明显下降.对于埋藏深度很浅的断层,当Asperity靠近断层上沿时,会显著增大其在地表投影附近的长周期地震动.能否合理地估计这些基本震源参数,是预测未来发震断层周围地震动场的关键.     

基于汶川MS8.0地震强震动记录的山体地形效应分析

2008年汶川M_S8.0地震中, 固定和流动地形影响台阵记录到大量主余震记录, 本文通过对其均方根加速度、 相对持时、 频谱等要素进行分析, 讨论了山体地形效应的特征及其影响因素. 对于自贡西山公园地形台阵各测点的分析结果显示: 该台阵山脚基岩位置地震动的均方根加速度和相对持时明显低于山体周边土层场地和山体基岩测点; 随着高程的增加, 山体基岩测点的均方根加速度逐渐变大, 相对持时则变化不大, 傅里叶谱形状也大体一致, 在2.0—5.0 Hz频段内有所放大; 山体周边土层场地和山体地形对于相同地震动输入中不同频段内地震动能量的放大水平不同, 从而导致二者的地表地震动强度产生显著差异, 且前者对地震动持时的增加更加显著.      

利用谱元法研究震源参数对于近断层地震动上盘效应的影响

国内外已有诸多学者基于强震记录或数值模拟方法开展了近断层地震动的上盘效应分析,并获得了初步的认识,但上盘效应随震源参数的变化规律仍有待深入探讨。本文使用运动学有限断层震源模型,运用高精度谱元法模拟逆断层破裂模式下近断层区域地震动,对比上、下盘地震动差异进而分析近断层地震动上盘效应。通过改变单一震源参数,研究断层上界埋深、震级大小以及断层倾角对地震动上盘效应的影响规律。研究结果表明：（1）使用运动学有限断层震源的谱元法数值模拟可以较好地反映近断层上盘效应;（2）上盘效应随测点到断层上界在地表投影的水平距离Rx的增加先增大后减小,最终趋于稳定。（3）上盘效应随断层上界埋深的增加先增大后减小,且随着断层上界埋深的增加,上盘效应峰值区会向远离断层破裂迹线的方向扩展。（4）上盘效应受矩震级影响较小,但总体随矩震级的增大而增大;上盘效应峰值区到断层破裂迹线的距离不随矩震级的变化而变化。（5）随着断层倾角的增加,上盘效应先增大后减小,当断层倾角为45°时上盘效应最为明显;随着断层倾角增加,上盘效应峰值区会向远离断层破裂迹线的方向扩展;当断层倾角为90°时不存在上盘效应。     

汶川MS8.0地震近断层强地面运动特征

详细研究2008年5月12日汶川8级地震近断层强地面运动时空分布特征,对揭示这次地震灾害分布特点及其成因具有重要意义。本文较为系统地研究了汶川地震近断层地震动特性(峰值、持时、不同周期的反应谱加速度值)的空间分布及其衰减特征,分析了断层距、场     

断层破裂传播速度与破坏性地震的烈度分布——浅源地震的断层不均匀性与短周期波动的多普勒效应

地震的等震线不仅反映了地震的大小,而且也反映了地震断层过程的类型和破裂速度.单侧破裂的断层过程呈现出蛋型的等震线,而双侧破裂的断层过程呈现出椭圆的等震线,等震线的长轴与短轴之比对于破裂传播速度十分敏感.本研究利用理论等震线与观测结果相比较的方法,确定了1964年日本新地震、1983年日本海中部地震、1975年中国海城地震和1976年中国唐山地震的破裂传播速度、断层类型以及断层走向.得到的断层破裂速度是剪切波的0.7—0.9倍.这些值比用长周期地震波所确定的要稍大.产生这种差异的原因是:对烈度起主要影响的短周期地震波强烈地依赖于小尺度的断层不均匀破裂过程,以及局部的破裂传播的开始和终止;而由长周期波所得到的破裂速度却反映了在整个断层上破裂传播的平均过程.根据等震线图所得出的断层类型及断层走向与其它独立方法的结果相一致.这意味着本方法可以应用于推断某些历史地震的断层类型、破裂传播速度及破裂传播方向.     

断层破裂传播速度与破坏性地震的烈度分布——浅源地震的断层不均匀性与短周期波动的多普勒效应

地震的等震线不仅反映了地震的大小,而且也反映了地震断层过程的类型和破裂速度.单侧破裂的断层过程呈现出蛋型的等震线,而双侧破裂的断层过程呈现出椭圆的等震线,等震线的长轴与短轴之比对于破裂传播速度十分敏感.本研究利用理论等震线与观测结果相比较的方法,确定了1964年日本新地震、1983年日本海中部地震、1975年中国海城地震和1976年中国唐山地震的破裂传播速度、断层类型以及断层走向.得到的断层破裂速度是剪切波的0.7——0.9倍.这些值比用长周期地震波所确定的要稍大.产生这种差异的原因是:对烈度起主要影响的短周期地震波强烈地依赖于小尺度的断层不均匀破裂过程,以及局部的破裂传播的开始和终止;而由长周期波所得到的破裂速度却反映了在整个断层上破裂传播的平均过程.根据等震线图所得出的断层类型及断层走向与其它独立方法的结果相一致.这意味着本方法可以应用于推断某些历史地震的断层类型、破裂传播速度及破裂传播方向.      

Geometric effects resulting from the asymmetry of dipping fault: Hanging wall/ footwall effects

Root-mean-square distance Drms with characteristic of weighted-average is introduced in this article firstly. Drms can be used to capture the general proximity of a site to a dipping fault plane comparing with the rupture distance Drup and the seismogenic distance Dseis. Then, using Drup, Dseis and Drms, the hanging wall/footwall effects on the peak ground acceleration (PGA) during the 1999 Chi-Chi earthquake are evaluated by regression analysis. The logarithm residual shows that the PGA on hanging wall is much greater than that on footwall at the same Drup or Dseis when the Drup or Dseis is used as site-to-source distance measure. In contrast, there is no significant difference between the PGA on hanging wall and that on footwall at the same Drms when Drms is used. This result confirms that the hanging wall/footwall effect is mainly a geometric effect caused by the asymmetry of dipping fault. Therefore, the hanging wall/footwall effect on the near-fault ground motions can be ignored in the future attenuation analysis if the root-mean-square distance Drms is used as the site-to-source distance measure.     

Development of attenuation relation for the near fault ground motion from the characteristic earthquake

A composite source model has been used to simulate a broadband strong ground motion with an associated fault rupture process. A scenario earthquake fault model has been used to generate 1 000 earthquake events with a magni-tude of Mw8.0. The simulated results show that, for the characteristic event with a strike-slip faulting, the character istics of near fault ground motion is strongly dependent on the rupture directivity. If the distance between the sites and fault was given, the ground motion in the forward direction (Site A) is much larger than that in the backward direction (Site C) and that close to the fault (Site B). The SH waves radiated from the fault, which corresponds to the fault-normal component plays a key role in the ground motion amplification. Corresponding to the sites A, B, and C, the statistical analysis shows that the ratio of their aPG is 2.15:1.5:1 and their standard deviations are about 0.12, 0.11, and 0.13, respectively. If these results are applied in the current probabilistic seismic hazard analysis (PSHA), then, for the lower annual frequency of exceedance of peak ground acceleration, the predicted aPG from the hazard curve could reduce by 30% or more compared with the current PSHA model used in the developing of seismic hazard map in the USA. Therefore, with a consideration of near fault ground motion caused by the rupture directivity, the regression model used in the development of the regional attenuation relation should be modified accordingly.     

Effects of hanging wall and footwall on demand of structural input energy during the 2008 Wenchuan earthquake

Systematic differences in the duration and frequency content of ground motions from the hanging wall and footwall during the 2008 Wenchuan earthquake are investigated,focusing on the influence of these differences on structural input energy based on the elastic and inelastic energy responses of structures.A comparison of the input energy spectra between the hanging wall and the footwall reveal that the structural input energy on the hanging wall is not amplified due to the short duration and low peak ground velocity to acceleration ratio(V/A).However,the larger demand of structural input energy on the footwall in the range of medium and long periods is observed and the demand increases up to 50% relative to the average level of structural input energy for rupture distances larger than 30 km.The importance of considering the footwall effect on structural input energy when comparing ground motions in the range of medium and long periods is recognized.     

Attenuation of peak ground accelerations from the great Wenchuan earthquake

Over 800 accelerograms recorded by 272 ground-level stations during the Wenchuan earthquake are used to analyze the influence of rupture distance, local site conditions and azimuth on peak ground accelerations (PGAs). To achieve a better understanding of the characteristics of ground motions, the spatial distributions of the EW, NS and UD components of PGAs arc obtained. Comparisons between the EW and NS components, the fault-normal and fault-parallel components,and the vertical and horizontal components of PGAs are performed, and the regression formula of the vertical-to-horizontal ratio of PGAs is developed. The attenuation relationship of peak horizontal accelerations (PHAs) is compared with several contemporary attenuation relationships. In addition, an analysis of residuals is conducted to identify the potential effects of rupture distance, azimuth and site conditions on the observed values of PHAs. The analysis focuses on medium-hard soil site conditions, as they provided most of the data used in this study.     

the faulting characteristics of 2008 wenchuan ms8.0 earthquake and its relation with strong ground motion

The 2008 M_S8 Wenchuan earthquake occurs on a high angle listric thrust fault. It is the first time that the near and far field strong ground motion was observed for such special type thrust earthquake. This paper jointly interprets the distribution of peak acceleration of ground motion data with seismogenic structure and slip propagating process to investigate how high angle listric thrust fault controls the pattern of strong ground motion. We found that the distribution of peak acceleration of strong ground motion during the Wenchuan earthquake has four distinctive features: 1)The peak acceleration of ground motion inside the Longmenshan fault zone is large, that is, nearly twice as strong as that outside the fault zone; 2)This earthquake produces significant vertical ground motion, prevailing against horizontal components in the near field; 3)The far field records show that the peak acceleration is generally higher and attenuates slower versus station-fault distance in the hanging wall. It is doubtful that the attenuation of horizontal components also has the hanging wall effect since no evidence yet proving that the unexpected high value at long distance need be omitted; 4)As to the attenuation in directions parallel to the source fault(Yingxiu-Beichuan Fault), the far field records also exhibit azimuthal heterogeneity that the peak acceleration of horizontal components decreases slower in the north-northeastern direction in which the co-seismic slip propagates than that in the backward way. However, the attenuation of vertical component displays very weak heterogeneity of this kind. Synthetically considered with shallow dislocation, high dip angle, and prevailing vertical deformation during co-seismic process of the Wenchuan earthquake, our near and far field ground motion records reflect the truth that the magnitude of ground motion is principally determined by slip type of earthquake and actual distance between the slipping source patches and stations. As a further interpretation, the uniqueness of high angle listric thrust results in that the ground motion effects of the Wenchuan earthquake are similar to that due to a common thrust earthquake in some components while differ in the others.     

汶川地震中强震动相对持时的空间变化特性研究

使用70％和90％能量持时定义,计算了汶川Ms8.0大地震中获取的来自109个台站强震动加速度记录的相对持时,并以此在竖向及两个水平向上分别进行了回归统计分析,得到了地震动持时的空间变化关系,给出了适合汶川地震地震动的持时定义.对比分析了上盘和下盘2个区域持时空间变化特征,进一步计算了地震动竖向持时与两个水平向持时的比...     

基于余震序列的地震烈度快速评估方法研究——以青海门源6.9级地震为例

地震烈度快速评估产品是破坏性地震发生后应急工作"黑箱期"内研判灾情的重要依据.文章基于青海门源6.9级地震震后2 h内的余震序列,采用最短断层距地震动衰减模型快速评估地震烈度.研究结果显示:利用震后30分钟内的余震序列得到的烈度分布可以初步判定重灾区及灾区范围,但灾区范围略小于实际调查结果;利用1.5 h内的余震序列得...