台湾集集地震近场地震动的上盘效应

1999年9月21日（当地时间）台湾集集7.6级地震是一个逆断层型地震．用回归分析法对台湾集集地震的加速度峰值数据进行分析，得出了这次地震的水平与垂直向的加速度峰值衰减关系．从残差分布上看，位于断层上盘和下盘上的加速度峰值与从衰减关系所得到的结果相比存在不同的系统偏差，断层上盘地表的加速度峰值较高，而下盘地表的加速度峰值较低．从这次地震的加速度峰值分布等值线图上也可以看出，加速度峰值的分布相对于断层呈现明显的不对称性，上盘衰减较慢而下盘衰减较快．在近断层强地面运动研究、地震危险性分析、设定地震研究与震害预测等工作中，应考虑可能地震的震源机制特点，以便使所用的衰减模型更能反映不同地震环境地区的地震动分布特征．      

Non‐structure‐specific intensity measure parameters and characteristic period of near‐fault ground motions

This paper focuses on the effects of long‐period pulse of near‐fault ground motions on the structural damage potential. Two sets of near‐fault ground motion records from Chi‐Chi, Taiwan earthquake and Northridge earthquake with and without distinct pulse are selected as the input, and the correlation analysis between 30 non‐structure‐specific intensity measure parameters and maximum inelastic displacements and energy responses (input energy and hysteretic energy) of bilinear single degree of freedom systems are conducted. Based on the frequency characteristic of near‐fault ground motions with remarkable long‐period components, two intensity indices are proposed, namely, the improved effective peak acceleration (IEPA) and improved effective peak velocity (IEPV). In addition a new characteristic period of these ground motions is defined based on IEPA and IEPV. Numerical results illustrate that the intensity measure parameters related to ground acceleration present the best correlation with the seismic responses for rigid systems; the velocity‐related and displacement‐related parameters are better for medium‐frequency systems and flexible systems, respectively. The correlation curves of near‐fault ground motions with velocity pulse differ from those of ground motions without pulse. Moreover, the improved parameters IEPA and IEPV of near‐fault impulsive ground motions enhance the performance of intensity measure of corresponding conventional parameters, i.e. EPA and EPV. The new characteristic period based on IEPA and IEPV can better reflect the frequency content of near‐fault ground motions. Copyright © 2009 John Wiley & Sons, Ltd.     

Earthquake fault‐induced surface rupture—A hybrid strong ground motion simulation technique and discussion for structural design

Unique to the near‐source region of a large earthquake is the occurrence of strong impulsive ground motion and surface faulting referred to as ‘fling‐step’ motion. The objective of this study is to synthesize broad‐band time histories over a wide range of frequencies by characterizing rupture directivity and fling effects from the comprehensive strong motion database of the near‐fault Chi‐Chi event. To aid in the generation of these special types of ground motions, a hybrid modeling technique is introduced based on the stochastic finite‐fault radiation method and an efficient analytical approach to incorporate the observed low‐frequency features in the records close to the ruptured fault. The results show that the overall agreement among the developed hybrid methodology and recorded waveforms and response spectra is quite satisfying. A brief discussion on the design of infrastructures near seismic fault is also included. Copyright © 2011 John Wiley & Sons, Ltd.     

Characteristics of amplitude and duration for near fault strong ground motion from the 1999 Chi-Chi, Taiwan Earthquake

A great number of free-field ground motion records are obtained during the 1999 Chi-Chi, Taiwan, earthquake. Records from 130 near fault free-field stations within 55 km to the causative fault surface are used as database, and characteristics of earthquake peak ground acceleration, velocity, displacement and duration are analyzed. According to this study, near fault ground motions are strongly affected by distance to fault, fault rupture directivity, site condition, as well as thrust of hanging wall. Compared with empirical strong ground motion attenuation relations used in China, US and Japan, the PGAs and PGVs recorded in this earthquake are not as large as what we have expected for a large earthquake as magnitude 7.6. However, the largest PGV and PGD worldwide were recorded in this event, which are 292 cm/s and 867 cm, respectively. Caused by nonlinear site effects of soil, peaks and corresponding ratios on E-class site were markedly different from those on other sites. Just as observed in historic earthquakes, fault rupture directivity effects caused significant differences between peaks of ground motion of two horizontal components, but took very slight effects on the duration of ground motion. The significant velocity pulses associated with large PGVs and PGDs, as well as large permanent displacements, which may result from the large thrust of the hanging wall, became the outstanding character of this event. Based on this study, we point out that 3D waveform modeling is needed to understand and predict near fault ground motion of large earthquakes.     

近断层地震动场预测——以长春市为例

断层带附近地震动场分布的研究,是当前地震工程领域研究的热点问题之一。近断层地震动场的分布对在断层附近进行抗震结构设计时,不仅是提供地震动输入,也是确定建设场地避让范围的重要依据之一。以区域地震构造背景分析、目标断层活动性鉴定、地震危险性评价为基础,结合断层探测结果,利用统计经验关系等最终确定发震断层,并建立相应的震源模型。采用显式有限元和并行计算技术计算目标区域场地的长周期地震动。利用有限断层随机合成的方法,计算高频地震动。将低频和高频地震动合成为目标区域内的宽频带地震动时程。对局部特殊场地条件地区,基于场地调查和勘探的数据,利用等效线性化等方法进行一维土层的非线性反应计算,给出这些特殊场地的宽频带地震动时程。最后,根据地震动时程获得设定地震发生时,目标区域的峰值加速度分布预测图和相应的反应谱。以长春市为例预测了在设定地震发生时,近断层地震动场的分布情况。当长春尖山子—卡伦断层发生6.0级地震时,潜在破坏性地震动的影响范围集中在附近,沿断层走向分布。加速度峰值沿断层垂直变化,主要为90 Gal～140 Gal。只是在长春市南部加速度峰值达到200 Gal。本研究的预测结果具备断层附近地震动的一些最基本的特征,符合当前对断层附近地震动的基本认识。     

Tall building performance‐based seismic design using SCEC broadband platform site‐specific ground motion simulations

The scarcity of strong ground motion records presents a challenge for making reliable performance assessments of tall buildings whose seismic design is controlled by large‐magnitude and close‐distance earthquakes. This challenge can be addressed using broadband ground‐motion simulation methods to generate records with site‐specific characteristics of large‐magnitude events. In this paper, simulated site‐specific earthquake seismograms, developed through a related project that was organized through the Southern California Earthquake Center (SCEC) Ground Motion Simulation Validation (GMSV) Technical Activity Group, are used for nonlinear response history analyses of two archetype tall buildings for sites in San Francisco, Los Angeles, and San Bernardino. The SCEC GMSV team created the seismograms using the Broadband Platform (BBP) simulations for five site‐specific earthquake scenarios. The two buildings are evaluated using nonlinear dynamic analyses under comparable record suites selected from the simulated BBP catalog and recorded motions from the NGA‐West database. The collapse risks and structural response demands (maximum story drift ratio, peak floor acceleration, and maximum story shear) under the BBP and NGA suites are compared. In general, this study finds that use of the BBP simulations resolves concerns about estimation biases in structural response analysis which are caused by ground motion scaling, unrealistic spectral shapes, and overconservative spectral variations. While there are remaining concerns that strong coherence in some kinematic fault rupture models may lead to an overestimation of velocity pulse effects in the BBP simulations, the simulations are shown to generally yield realistic pulse‐like features of near‐fault ground motion records.     

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.     

Empirical attenuation relationship for Arias Intensity

Arias Intensity is a ground motion parameter that captures the potential destructiveness of an earthquake as the integral of the square of the acceleration–time history. It correlates well with several commonly used demand measures of structural performance, liquefaction, and seismic slope stability. A new empirical relationship is developed to estimate Arias Intensity as a function of magnitude, distance, fault mechanism, and site category based on 1208 recorded ground motion data from 75 earthquakes in active plate‐margins. Its functional form is derived from the point‐source model, and the coefficients are determined through non‐linear regression analyses using a random‐effects model. The results show that for large magnitude earthquakes (M > 7) Arias Intensity was significantly overestimated by previous relationships while it was underestimated for smaller magnitude events (M ? 6). The average horizontal Arias Intensity is not significantly affected by forward rupture directivity in the near‐fault region. The aleatory variability associated with Arias Intensity is larger than that of most other ground motion parameters such as spectral acceleration. However, it may be useful in assessing the potential seismic performance of stiff engineering systems whose response is dominated by the short‐period characteristics of ground motions. Copyright © 2003 John Wiley & Sons, Ltd.     

直下型断层的破裂速度对盆地地震效应的影响

首先基于有限断层破裂下的运动学震源模型,对比验证了三维谱元法对于近场地震动的模拟精度。 进而通过含盆地模型与不含盆地的一维水平成层模型的地震动强度之间和放大系数分布特征之间的对比,详细研究了直下型断层的破裂速度对盆地地震效应的影响。结果表明,盆地的存在会显著改变近断层地震动的分布特征,同时盆地内不同分量强地震动的分布特征变化较大。断层破裂速度对盆地地震效应影响显著,随破裂速度的增大盆地地震动强度逐渐增加,但不同分量上地震动强度的增加速率显著不同,受盆地效应的影响,放大系数表现出与强地震动不同的分布特征。盆地放大系数整体表现出随破裂速度的增加而减小的趋势,但不同分量放大系数所受影响程度差异明显。同时,盆地内地震动强烈放大区域的位置也受破裂速度的显著影响,但其总体上集中在断层两侧区域及垂直于破裂方向的盆地边缘附近。      

The response law of far-field seismic ground motion of the Wenchuan earthquake and its damaging mechanism in the Loess Plateau

A series of housing collapses and other serious damage was caused by the 2008 Wenchuan M_S 8.0 earthquake in the seismic intensity Ⅵ areas of the Loess Plateau, which is hundreds of kilometers away from the epicenter, and which showed a remarkable seismic intensity anomaly. The seismic disasters are closely related to the seismic response characteristics of the site, therefore, the systematic study of the far-field seismic response law of the Wenchuan earthquake in the Loess Plateau is of great significance to prevent the far-field disaster of great earthquake. In this paper, the seismic acceleration records of several bedrock stations and loess stations from the seismogenic fault of the Wenchuan earthquake to the Loess Plateau were collected, and the attenuation law of ground motion along the propagation path and the characteristics of seismic response on the loess site are studied, and the mechanism of amplification effect of ground motion is analyzed based on the dynamic feature parameters of the loess site obtained through the HVSR method. Taking a typical loess site of thick deposit as the prototype, a series of shaking table tests of dynamic response of loess site models with different thicknesses were carried out. Amplification effect, spectral characteristics of acceleration in model sites were analyzed under the action of a far-field seismic wave of the Wenchuan earthquake. The results show that seismic attenuation on the propagation path along the NE strike of the seismogenic fault to the Loess Plateau is slower than that in other directions, and the predominant period range of ground motion on bedrock site of the Loess Plateau presents broadband characteristics. Because the natural periods of loess sites with thick deposits are within the predominant period range of bedrock input wave, loess sites appear significant amplification effect of ground motion, the horizontal acceleration of ground motion exceeds 0.1 ?g, the seismic intensity reaches 7°. The thicker the loess deposit is, the more significant the change of spectral characteristics of ground motion on loess sites, and the narrower the predominant period range of ground motion becomes, and the closer it is to the natural period of loess sites. Therefore, for some old houses on thick loess sites, the poor seismic performance and strong seismic response eventually led to their collapses and damages because their natural periods are very close to the predominant period of ground motion of the Wenchuan earthquake on thick loess sites; For these damaged high-rise buildings, the resonance effect might be the main reason for their damages because their natural periods are included in the predominant period range of ground motion of the Wenchuan earthquake on thick loess sites.These research results would provide a basis for seismic disasters prediction and evaluation and seismic design of construction engineering in the Loess Plateau.     

震源破裂方式和断层性质对近场强地震动特征的影响

基于数值格林函数法的近场强地震动数值模拟方法,以1994年Northridge地震断层面上位错量的不均匀分布模式和该地区的地层剪切波速度结构为震源模型和计算模型,做了两个方面的模拟研究:(1)直立走滑断层(断层倾角为90°)情况下,模拟分析了有限断层单侧破裂模式和双侧破裂模式对强地震动特征——破裂方向性和上盘效应的影响;(2)对于倾斜断层(倾角为45°),模拟分析了正断层、逆断层和走滑断层情况下,单侧破裂模式对其强地震动主要特征——破裂方向性效应和上盘效应的影响.结果表明:断层的破裂方式直接影响着地表地震动峰值和矢量分布;在近场区无论直立断层还是倾斜断层,其地表地震动峰值分布所表达的破裂方向性效应显著,位于破裂传播前方的地震动强度大,反映了波前被压缩的趋势,破裂后方地震强度明显变小;倾斜断层引起的上盘效应明显,NS向分量和竖向分量的地表地震动峰值的最大值出现在上盘靠近断层迹线处,EW向分量的峰值在断层迹线两侧呈不对称分布,且逆断层引起的地震动峰值最大,走滑断层的次之,正断层的最小.     

Seismic isolation of cable‐stayed bridges for near‐field ground motions

This study examines the efficacy of using seismic isolation to favorably influence the seismic response of cable‐stayed bridges subjected to near‐field earthquake ground motions. In near‐field earthquake ground motions, large amplitude spectral accelerations can occur at long periods where many cable‐stayed bridges have significant structural response modes. This combination of factors can result in large tower accelerations and base shears. In this study, lead–rubber bearing seismic isolators were modeled for three cable‐stayed bridges, and three cases of isolation were examined for each bridge. The nine isolated bridge configurations, plus three non‐isolated configurations as references, were subjected to near‐field earthquake ground motions using three‐dimensional time‐history analyses. Introduction of a small amount of isolation is shown to be very beneficial in reducing seismic accelerations and forces while at the same time producing only a modest increase in the structural displacements. There is a low marginal benefit to continue to increase the amount of isolation by further lengthening the period of the structure because structural forces and accelerations reduce at a diminishing rate whereas structural displacements increase substantially. In virtually all cases the base shears in the isolated bridges were reduced by at least 50several instances by up to 80individual near‐field records showed large variability from one record to the next, with coefficients of variation about the mean as large as 50assessing the characteristics of near‐field ground motion for use in isolation design of cable‐stayed bridges. Copyright © 2003 John Wiley & Sons, Ltd.     

Input and system identification of the Hualien soil–structure interaction system using earthquake response data

This paper presents an input and system identification technique for a soil–structure interaction system using earthquake response data. Identification is carried out on the Hualien large‐scale seismic test structure, which was built in Taiwan for international joint research. The identified quantities are the input ground acceleration as well as the shear wave velocities of the near‐field soil regions and Young's moduli of the shell sections of the structure. The earthquake response analysis on the soil–structure interaction system is carried out using the finite element method incorporating the infinite element formulation for the unbounded layered soil medium and the substructured wave input technique. The criterion function for the parameter estimation is constructed using the frequency response amplitude ratios of the earthquake responses measured at several points of the structure, so that the information on the input motion may be excluded. The constrained steepest descent method is employed to obtain the revised parameters. The simulated earthquake responses using the identified parameters and input ground motion show excellent agreement with the measured responses. Copyright © 2003 John Wiley & Sons, Ltd.     

近断层地震动破裂向前方向性与滑冲效应对隔震建筑结构抗震性能的影响

选择台湾集集地震和美国北岭地震的近断层地震动记录作为输入,考察了近断层地震动破裂向前方向性与滑冲效应引起的两种不同速度脉冲运动对单自由度体系和长周期橡胶支座隔震建筑结构抗震性能的影响.反应谱分析表明,破裂向前方向性与滑冲效应对工程结构地震响应的影响是随结构周期变化的.在中短周期段,含破裂向前方向性效应地震动的谱加速度值大于含滑冲效应地震动的谱加速度值;而在长周期段,含滑冲效应地震动的谱加速度大于含破裂向前方向性效应的谱加速度值.并且,与无脉冲地震动作用相比,含破裂向前方向性与滑冲效应脉冲的近断层地震动作用下隔震建筑的地震响应显著增大.滑冲效应引起的速度脉冲使隔震建筑底部的层间变形和楼层剪力明显增大,这意味着滑冲效应脉冲比向前方向性效应脉冲对长周期建筑结构的破坏更具危害性.     

Modeling of the ground motion for the Petropavlovsk earthquake of November 24, 1971 (M = 7.6)

Based on the example of the strong earthquake of November 24, 1971, with the earthquake source near the Petropavlovsk-Kamchatskii, the new modeling technique of the strong ground motions within the broadband is tested. In this technique, the seismologically-substantiated models of the radiation source and elastic medium are used. The source is represented by an array of point radiation sources-dislocations with the random seismic moments (amplitudes) and with the random time functions. The new method of calculation of the Green functions is developed to describe the propagation of waves and residual displacements of a layered medium. The method is used for the simulation of the horizontal ground motion, recorded by a S5S-ISO instrument for the strong earthquake that took place on November 24, 1971 with the source near the Petropavlovsk-Kamchatskii (with a depth of 105 km). The position of the hypocenter, the sizes and the position of the fault, and “fault mechanism” were considered to be known a priori. By a trial and error method of the duration of the source process and only two spectral parameters, it was possible to simulate successfully the fundamental characteristics of the ground vibrations: the amplitude of acceleration, the velocity and displacement of the ground, their Fourier spectrum, the duration of the vibrations, and the response spectrum. The surprisingly high level of high-frequency radiation, probably connected with the intraplate position of the source, is a specific feature of the source.     

Effects of near-fault and far-fault ground motions on nonlinear dynamic response and seismic damage of concrete gravity dams

As the forward directivity and fling effect characteristics of the near-fault ground motions, seismic response of structures in the near field of a rupturing fault can be significantly different from those observed in the far field. The unique characteristics of the near-fault ground motions can cause considerable damage during an earthquake. This paper presents results of a study aimed at evaluating the near-fault and far-fault ground motion effects on nonlinear dynamic response and seismic damage of concrete gravity dams including dam-reservoir-foundation interaction. For this purpose, 10 as-recorded earthquake records which display ground motions with an apparent velocity pulse are selected to represent the near-fault ground motion characteristics. The earthquake ground motions recorded at the same site from other events that the epicenter far away from the site are employed as the far-fault ground motions. The Koyna gravity dam, which is selected as a numerical application, is subjected to a set of as-recorded near-fault and far-fault strong ground motion records. The Concrete Damaged Plasticity (CDP) model including the strain hardening or softening behavior is employed in nonlinear analysis. Nonlinear dynamic response and seismic damage analyses of the selected concrete dam subjected to both near-fault and far-fault ground motions are performed. Both local and global damage indices are established as the response parameters. The results obtained from the analyses of the dam subjected to each fault effect are compared with each other. It is seen from the analysis results that the near-fault ground motions, which have significant influence on the dynamic response of dam–reservoir–foundation systems, have the potential to cause more severe damage to the dam body than far-fault ground motions.     

西昌断陷盆地场地地震动差异分析

以汶川地震中的非发震断层安宁河断裂带周边西昌地区所获取的加速度记录为依据,研究了这些记录在峰值、频谱之间的差异,并通过这些地区的局部场地条件差异进行了初步解释。在此基础上通过数值模拟方法,利用基于显式有限元和局部透射人工边界的二维有限元模型对该地区的地面运动进行了模拟。数值试验结果表明：这些简单的理想化模型对这一地区地震动的本质特征进行重现,并对产生地面运动差异的机理进行合理解释。通过分析,初步揭示了由深部断层构造所控制的断陷盆地对地震动影响显著。     

Seismic base‐isolation by use of a telescoping stepping mechanism

A new base‐isolation mechanism corresponding to a variance of the stepping A‐shaped frame is proposed and its seismic performance is investigated numerically for strong ground accelerations with peak values in the range from 0.5 to 1g. In its simplest two‐dimensional form, the system consists of a frame with two telescoping legs pinned at the apex at a sharp angle. The legs are attached to the foundation through a spring and a damper acting in parallel. Both the springs and viscous dampers have bilinear characteristics that make them very stiff in compression but very soft in tension. As the structure rocks sideways, the length of the loaded leg remains essentially constant while the length of the unloaded leg increases. When the ground acceleration changes direction, the process is reversed. The resulting system has three main characteristics: (i) as the structure steps on a rigid leg, the maximum acceleration that can be transmitted to the superstructure is limited to a value which is approximately independent of the amplitude of the ground motion; (ii) there is a systematic lifting of the superstructure with kinetic energy being systematically transformed into potential energy during the strong phase of the ground motion; and (iii) the system is slowly self‐centering at the end of the earthquake. The seismic performance of the system is evaluated for a tall bridge pier and for a smaller frame that could be used in a multi‐story building. The results obtained for the 1940 El Centro ground motion scaled to 1g and for the near‐field Rinaldi ground motion recorded during the Northridge earthquake show that substantial reductions of the absolute acceleration can be obtained with reasonable relative displacements of the superstructure and small strokes in the isolation devices. Copyright © 2004 John Wiley & Sons, Ltd.     

Time series decomposition of groundwater level changes in wells due to the Chi‐Chi earthquake in Taiwan: a possible hydrological precursor to earthquakes

The largest and most disastrous earthquake in Taiwan (Mw: 7·3) in the 20th century, the Chi‐Chi earthquake, hit central Taiwan at 01:47 local time on September 21, 1999. The groundwater level changes were rapid at that time. Studies have found that the rapid change in groundwater levels was a co‐seismic phenomenon. This work analyzes the possibility that the abnormal change in groundwater levels may have occurred before the earthquake. Three well stations with a total of five wells are considered. They are all near the Che‐Lung‐Pu fault, which caused the Chi‐Chi earthquake. The time series decomposition method was applied to decompose the seasonal groundwater level, the trend in groundwater levels, and the period of the change in the groundwater level. Residual groundwater levels were found by subtracting the determined seasonal, trend and period data from corresponding data for the original groundwater level. The computed residual water levels in July, August and September of 1999, were transformed into a frequency spectrum by a Fourier method. Additionally, the effects of barometric pressures on the groundwater level changes were also evaluated. Analytical results show that the spectral density functions of the irregular groundwater level in the confined aquifer at the Chu‐Shan well in September behaved differently from those in July and August. We posit that a pre‐seismic hydrogeological anomaly may have existed before the Chi‐Chi earthquake, and can be considered in future studies of anomalies associated with earthquakes. Copyright © 2007 John Wiley & Sons, Ltd.     

西昌断陷盆地场地地震动差异分析

以汶川地震中的非发震断层安宁河断裂带周边西昌地区所获取的加速度记录为依据,研究了这些记录在峰值、频谱之间的差异,并通过这些地区的局部场地条件差异进行了初步解释。在此基础上通过数值模拟方法,利用基于显式有限元和局部透射人工边界的二维有限元模型对该地区的地面运动进行了模拟。数值试验结果表明：这些简单的理想化模型对这一地区地震动的本质特征进行重现,并对产生地面运动差异的机理进行合理解释。通过分析,初步揭示了由深部断层构造所控制的断陷盆地对地震动影响显著。