成都盆地不同工程地质分区内场地地震动参数的计算分析

场地条件对地震动幅值和频谱特性均有影响, 现行的中国地震动参数区划图根据场地类别调整地震动反应谱特征周期, 但尚未考虑到对地震动峰值和反应谱平台值的调整. 以成都盆地为例, 广泛收集了盆地范围内的工程钻孔资料. 考虑到不同工程地质分区内场地地震动参数可能存在较大差异, 在研究区工程地质分区的基础上, 利用等效线性化方法对钻孔进行了土层地震反应分析, 给出了成都盆地内不同工程地质分区的地震动参数调整系数建议值.     

A stochastic ground motion model with separable temporal and spectral nonstationarities

A fully nonstationary stochastic model for strong earthquake ground motion is developed. The model employs filtering of a discretized white‐noise process. Nonstationarity is achieved by modulating the intensity and varying the filter properties in time. The formulation has the important advantage of separating the temporal and spectral nonstationary characteristics of the process, thereby allowing flexibility and ease in modeling and parameter estimation. The model is fitted to target ground motions by matching a set of statistical characteristics, including the mean‐square intensity, the cumulative mean number of zero‐level up‐crossings and a measure of the bandwidth, all expressed as functions of time. Post‐processing by a second filter assures zero residual velocity and displacement, and improves the match to response spectral ordinates for long periods. Copyright © 2008 John Wiley & Sons, Ltd.     

Analysis of the relations between slope failure distribution and seismic ground motion during the 2008 Wenchuan earthquake

The 2008 Wenchuan earthquake with M_w7.9 occurred at Yingxiu County in Longmenshan thrust fault belt, southwest China, having triggered a huge amount of slope failures. This paper applied a detailed inventory with more than 190,000 slope failures and strong ground motion records of 187 seismic stations to analyze the qualitative and quantitative relations between slope failure distribution and seismic parameters. The results revealed that slope failure distribution was exponentially decreased with the increment of epicentral distance and distance from surface fault rupture; peak ground acceleration (PGA) on the hanging wall side was apparently larger than that on footwall side. Linear correlation between concentration of slope failures (LNC) and the percentage of the area affected by slope failure (LAP) and PGA was demonstrated by statistical analysis, which revealed that 0.18~0.21 g horizontal PGA was the threshold value of the occurrence of slope failure. Furthermore, this paper presented an empirical model for the attenuation relation of slope failure distribution.     

Strong ground acceleration seismic hazard in Greece and neighboring regions

In an early paper [Tectonophysics 117 (1985) 259] seismic hazard in Greece was analyzed using a relatively homogeneous earthquake catalogue spanning 1900–1978 and a strong motion attenuation relationship adapted to use in Greece. Improved seismic hazard analyses are obtained here using Gumbel's asymptotic extreme value distribution applied to peak horizontal ground acceleration occurrence, but now taking into account the increased length and quality of earthquake catalogue data spanning 1900–1999 and the burgeoning information on earthquake strong motion data and attenuation relationships appropriate for Europe and, explicitly, Greece. Seismic acceleration hazard results tabulated for six cities reveal (e.g. using arbitrarily the 50-year p.g.a. with 90% probability of not being exceeded) changes of about 10% in the new calculated values: two cities show an increase and four a decrease. These are relatively small and reassuring adjustments.Inspection of the available attenuation relationships leads to a preference for the models of Theodulidis and Papazachos, particularly with the model modification to produce a ‘stiff soil’ site relationship, as these relationships explicitly exploit the Greek strong motion database. Isoacceleration maps are produced for Greece as a whole from each attenuation relationship inspected. The final set of maps based on the Theodulidis and Papazachos models provide a foundation for comparison with the Seismic Hazard Zones adopted in the New Greek Seismic Code where scope can be found to modify zone shape and the level at which p.g.a.s are set. It should be noted that the generation of the present isoacceleration maps is based on a seismogenic zone-free methodology, independent of any Euclidean zoning assumptions.     

2015年4月25日尼泊尔地震波场传播及烈度初步模拟分析

2015年4月25日尼泊尔发生Mw7.9地震.本文采用三维曲线坐标网格有限差分方法,依据USGS给出的震源运动学反演结果和震源区域地形数据,模拟了尼泊尔地震波场传播过程,得到震源区域烈度分布模拟结果,与实际观测的地表峰值速度(PGV)大体吻合.结果表明:地震烈度的空间分布整体上受控于震源的单边破裂特征,高烈度区域主要分布在破裂传播方向上,即震源东半部.震源南侧到东南侧近场,由于受到震源和地形的双重影响,形成最大烈度分布区域,最大烈度约为IX.南侧平原受低速沉积层影响形成高烈度区域.震源西侧及盆地内烈度相对较低.     

2014年2月12日新疆于田地震强地面运动初步模拟及烈度预测

2014年2月12日新疆自治区于田县发生了MS7.3级地震.在已知的三维介质模型、地形数据基础上,利用震源运动学初步反演模型（张勇等,2014）,作者采用曲线坐标网格三维曲线有限差分方法模拟了于田地震波场传播过程,并计算了模拟区域地震烈度分布.结果表明：地震最大烈度为7度,距离震中最近的于田县城烈度约为5度,断层西北侧地面震动略强于断层东南侧.另外模拟结果还显示地震动在山脊处具有较大的幅度.该地震本身主要能量释放区域在中地壳,主要滑动未及地表,因此对地表造成的破坏有限,这与目前尚无人员伤亡报告的情况相符合.     

2014年8月3日云南鲁甸地震强地面运动初步模拟及烈度预测

2014年8月3日云南省昭通市鲁甸县发生了Ms6.5级地震.在已知的三维介质模型、地形数据基础上,利用震源运动学初步反演模型（张勇等,2014）,作者采用曲线坐标网格三维曲线有限差分方法模拟了鲁甸地震波场传播过程,并计算了模拟区域地震烈度分布.结果表明：地震最大烈度为Ⅶ度,破坏主要集中在鲁甸县以及巧家县、会泽县靠近鲁甸县的边界.另外,模拟结果还显示地震动在山峰、山脊处具有较大的幅度.计算表明断层东北侧的低速沉积盆地的波动放大效应加强了该地区的地震灾害.     

A ground motion selection procedure for enforcing hazard consistency and estimating seismic demand hazard curves

This paper develops a procedure to select unscaled ground motions for estimating seismic demand hazard curves (SDHCs) in performance‐based earthquake engineering. Currently, SDHCs are estimated from a probabilistic seismic demand analysis, where several ensembles of ground motions are selected and scaled to a user‐specified scalar conditioning intensity measure (IM). In contrast, the procedure developed herein provides a way to select a single ensemble of unscaled ground motions for estimating the SDHC. In the context of unscaled motions, the proposed procedure requires three inputs: (i) database of unscaled ground motions, (ii) I M , the vector of IMs for selecting ground motions, and (iii) sample size, n; in the context of scaled motions, two additional inputs are needed: (i) a maximum acceptable scale factor, SF_max, and (ii) a target fraction of scaled ground motions, γ. Using a recently developed approach for evaluating ground motion selection and modification procedures, the proposed procedure is evaluated for a variety of inputs and is demonstrated to provide accurate estimates of the SDHC when the vector of IMs chosen to select ground motions is sufficient for the response quantity of interest. Copyright © 2015 John Wiley & Sons, Ltd.     

2008年青海大柴旦Mw6.3地震地面运动模拟

2008年11月10日在青海柴达木盆地北缘发生了大柴旦M_W6.3地震,为了研究该地震的区域地震波传播与地面运动特征,本文利用地质资料和地壳速度结构研究成果,构建了柴达木盆地及周边区域三维传播介质模型,采用有限差分方法模拟了大柴旦地震波场传播过程以及地面运动分布特征.结果表明,柴达木盆地对波场传播有明显影响,表现为地震波传入盆地后在边界产生次生面波,盆地沉积物对地震波具有围陷作用,地震地面运动在盆地内振幅增大、持时延长.模拟结果给出的地震地面运动峰值速度分布以及理论地震图均和观测结果符合较好,反映数值模拟较好地给出了观测地面运动的主要特征以及传播介质模型的合理性.     

Re-evaluation of seismic torsional provisions

Traditionally, seismic torsional provisions have been evaluated based on the assumption that the strength of the lateral load resisting elements can be adjusted without changing their stiffness. There is an important class of elements that a change of their lateral strength implies a corresponding change of stiffness, as exemplified by reinforced concrete flexural walls. This would imply that when torsional provisions are applied to adjust the strengths of these elements, the stiffness distribution, and also the eccentricity of the system, will change. This paper re-evaluates the consequences of applying the torsional provisions of the Uniform Building Code (UBC, 1997) and also the Eurocode (Eurocode 8, 1994) to single mass eccentric systems supported by elements having such characteristics. In conjunction with the results based on the traditional assumption, the effectiveness of the two provisions to mitigate torsional effects is discussed from a broader perspective. Copyright © 1999 John Wiley & Sons, Ltd.     

A new approach of selecting real input ground motions for seismic design: The most unfavourable real seismic design ground motions

This paper presents a new way of selecting real input ground motions for seismic design and analysis of structures based on a comprehensive method for estimating the damage potential of ground motions, which takes into consideration of various ground motion parameters and structural seismic damage criteria in terms of strength, deformation, hysteretic energy and dual damage of Park & Ang damage index. The proposed comprehensive method fully involves the effects of the intensity, frequency content and duration of ground motions and the dynamic characteristics of structures. Then, the concept of the most unfavourable real seismic design ground motion is introduced. Based on the concept, the most unfavourable real seismic design ground motions for rock, stiff soil, medium soil and soft soil site conditions are selected in terms of three typical period ranges of structures. The selected real strong motion records are suitable for seismic analysis of important structures whose failure or collapse will be avoided at a higher level of confidence during the strong earthquake, as they can cause the greatest damage to structures and thereby result in the highest damage potential from an extended real ground motion database for a given site. In addition, this paper also presents the real input design ground motions with medium damage potential, which can be used for the seismic analysis of structures located at the area with low and moderate seismicity. The most unfavourable real seismic design ground motions are verified by analysing the seismic response of structures. It is concluded that the most unfavourable real seismic design ground motion approach can select the real ground motions that can result in the highest damage potential for a given structure and site condition, and the real ground motions can be mainly used for structures whose failure or collapse will be avoided at a higher level of confidence during the strong earthquake. Copyright © 2007 John Wiley & Sons, Ltd.     

Comparing the adequacy of alternative ground motion intensity measures for the estimation of structural responses

Practical methods for the probability‐based seismic assessment of structures make use of estimates of demands produced by earthquakes of different intensities. The uncertainties associated with these estimates are highly dependent on the variable adopted as the intensity measure (IM, e.g., PGA, spectral acceleration, etc.). This generates the need to compare the efficiency of an originally adopted IMwith that of a new candidate. This implies comparing the dispersion of the demand measure (DM, e.g., maximum interstorey drift ratio, ductility demand, etc.) conditional to each of the two IMs. In order to obtain the demand estimates in a conventional way, a full set of dynamic response analyses should be performed for each IM under scrutiny, i.e., multiple records scaled at several fixed values of each IM. The procedure developed here serves to accelerate this comparison avoiding the effort required to evaluate the dynamic responses of the structure for all the ground motion time histories considered every time that a new IM is adopted. For this purpose, use is made of available results of analyses performed for a different (i.e., the original) IM. Two methods are proposed: the direct method involves performing a regression of the results obtained from the original analyses, taking the candidate IM as the independent variable. The indirect method involves rebuilding the probability density function of the DM given a defined value of the candidate IM by means of the total probability theorem, using the results of the original analyses and certain data relating the two IMs. The proposed methods have been tested by application to several SDOF systems with different periods and different cyclic‐response backbone curves. The conditions affecting their approximation are explored, and some criteria to improve them are identified. The procedure can also be used to determine the optimum value of a parameter to be used in a parameter‐based IM. Copyright © 2004 John Wiley & Sons, Ltd.     

Characterization of seismic hazard and structural response by energy flux

Seismic safety of structures depends on the structure's ability to absorb the seismic energy that is transmitted from ground to structure. One parameter that can be used to characterize seismic energy is the energy flux. Energy flux is defined as the amount of energy transmitted per unit time through a cross-section of a medium, and is equal to kinetic energy multiplied by the propagation velocity of seismic waves. The peak or the integral of energy flux can be used to characterize ground motions. By definition, energy flux automatically accounts for site amplification. Energy flux in a structure can be studied by formulating the problem as a wave propagation problem. For buildings founded on layered soil media and subjected to vertically incident plane shear waves, energy flux equations are derived by modeling the building as an extension of the layered soil medium, and considering each story as another layer. The propagation of energy flux in the layers is described in terms of the upgoing and downgoing energy flux in each layer, and the energy reflection and transmission coefficients at each interface. The formulation results in a pair of simple finite-difference equations for each layer, which can be solved recursively starting from the bedrock. The upgoing and downgoing energy flux in the layers allows calculation of the energy demand and energy dissipation in each layer. The methodology is applicable to linear, as well as nonlinear structures.     

基于假设检验的地震动强度(烈度)速报方法

地震发生后数分钟内,快速、可靠地判别出地震动强度(烈度)的空间分布,用以估计不同地区的受灾程度,可以为政府开展应急救援并合理分配救援力量提供决策依据,保证救援人员及时、准确地到达极震区并展开搜救,以减少生命财产损失。本文基于统计学中的假设检验方法,对历史震害资料进行统计,提出了一种利用强地震动参数判别地震动强度(烈度)的方法。比较结果表明,本方法所确定的地震动强度(烈度)与实际震害烈度对应较好,能较真实地反映实际震害情况。     

On planar seismic wavefront modeling for estimating rotational ground motions: Case of 2-D SH line-source

At large hypocentral distances, it is convenient to approximate the curved transient seismic wavefronts as planar to estimate rotational ground motions from the single-station recordings of translational ground motions. In this paper, we investigate whether and when this approximation, referred to as the ‘plane-wave’ approximation, can be considered adequate close to the source. For this, we consider a simplistic source model comprising a two-dimensional, kinematic shear dislocation SH line-source buried in a homogenous, elastic half-space and assume this to be an equivalent representation of a finite-sized fault. The ‘plane-wave’ rotational motion is then synthesized from the exact translational motion solution to the assumed model and compared with the exact rotational motion solution for this model. The comparison between the two sets of rotational amplitudes in frequency domain suggests that the plane-wave approximation may be adequate, when the wavelengths of the seismic waves are much smaller than the source depth. When this is not true, the plane-wave approximation is seen to underestimate the Fourier amplitudes close to the source by several orders, particularly when the fault planes are vertically oriented. A similar comparison in the time domain indicates that a severe underestimation may also occur when the source rise time is longer than the shear-wave arrival time at the epicenter. Significant discrepancies are also observed between the waveforms of the exact and plane-wave rotational motions.     

2013年甘肃岷县MS6.6地震区域地震波传播模拟与地面运动特征研究

2013年7月22日,甘肃省定西市岷县发生M_S6.6地震,造成了严重的人员伤亡和经济损失.地震发生于青藏高原东北部边缘与甘肃东南部地区的交界处,是该区域一百多年以来发生的最大地震.分析本次地震观测数据显示,岷县M_S6.6地震产生的地震地面运动呈现出明显的区域变化特征.为了研究这种区域变化特征,本文使用全球CRUST1.0和SRTM30模型数据建立了甘肃岷县及周边地区的地下三维传播介质模型,使用并行的三维有限差分方法进行了岷县地震的区域地震波传播模拟,并与研究区内数字地震台网记录的地震观测资料进行对比.通过分析地面运动的峰值速度和持续时间的区域分布特征,发现：在青藏高原东北部边缘,较大的地形起伏对地面运动的峰值速度分布起主要影响作用;在青藏高原外围地区,地形起伏较小,而沉积层主要影响地面运动的峰值速度和持续时间,从而导致了明显的盆地效应,如地面运动的振幅放大和持续时间加长.因此,研究区剧烈的地形起伏和表层沉积层是影响地面运动的重要因素.

     

Strength reduction factors for seismic analyses of buildings exposed to near-fault ground motions

To estimate the near-fault inelastic response spectra, the accuracy of six existing strength reduction factors (R) proposed by different investigators were evaluated by using a suite of near-fault earthquake records with directivity-induced pulses. In the evaluation, the force-deformation relationship is modelled by elastic-perfectly plastic, bilinear and stiffness degrading models, and two site conditions, rock and soil, are considered. The R-value ratio (ratio of the R value obtained from the existing R-expressions (or the R-μ-T relationships) to that from inelastic analyses) is used as a measurement parameter. Results show that the R-expressions proposed by Ordaz & Perez-Rocha are the most suitable for near-fault ground motions, followed by the Newmark & Hall and the Berrill et al. relationships. Based on an analysis using the near-fault ground motion dataset, new expressions of R that consider the effects of site conditions are presented and verifi ed.     

Study on the severest real ground motion for seismic design and analysis

How to select the adequate real strong earthquake ground motion for seismic analysis and design of trucures is an essential problem in earthquake engineering research and practice.In the paper the concept of the severest design ground motion is proposed and a method is developed for comparing the severity of the recorded strong ground motions.By using this method the severest earthquake ground motions are selected out as seismic inputs to the structures to be designed from a database that consists of more than five thousand significant strong ground moton records collected over the world.The selected severest ground motions are very likely to be able to drive the structures to their critical response and thereby result in the highest damage potential.It is noted that for different structures with diffferent predominant natural periods and at different sites where structures are located the severest design ground motions are usually different.Finally.two examples are illustrated to demonstrate the rationality of the concept and the reliability of the selected design motion.