Earthquake ground motion simulation with frequency-dependent soil properties

A one-dimensional earthquake ground motion simulation with frequency-dependent dynamic soil parameters, which include shear wave velocity and quality factor, is performed within the frequency band between 10⁻² and 30 Hz. For the simulation, the general frequency-dependent dynamic soil properties are obtained by using a new non-resonance technique on various soils. Comparisons between transfer functions involving frequency-dependent and -independent dynamic soil parameters indicate that soil amplification throughout the considered frequency range is sensitive to the values of the dynamic soil parameters, in particular to the quality factor. Simplification of frequency-dependent dynamic soil parameters into constants, which prevail as a convenient practice, incurs large amplitude distortion. This study therefore demonstrates that the dynamic properties of soils play an important role in the near surface earthquake ground motion analyses and need to be used in the same way as how they were measured.     

层状介质中有限震源引起的地面运动的计算对点源情形的拓展

从分层均匀介质中地震波传播的基本理论出发, 参考已有的利用广义反射透射系数矩阵方法计算分层均匀介质中点源引起的地面运动的方法和程序, 考虑了任意几何特征的有限震源及有限震源的震源机制随时间和空间发生变化的可能性, 并考虑了并行计算的发展方向, 本文对点源情况下的计算流程进行了改进, 重新设计编写了计算程序GRTMatSyn, 使其不但适应于点源的情形, 也适应于任意几何形状的、 有限的、 震源机制随时间和空间变化的有限震源的情形． 为了验证该程序的可靠性和计算效率, 设计了必要的有限震源模型和观测点分布, 计算了地面运动, 并与已有的被广泛认可的计算有限平面断层引起的地面运动的程序CompSyn的计算结果进行了对比分析． 结果表明, GRTMatSyn的计算结果可靠、 计算效率较高．      

Kinematic source model for simulation of near-fault ground motion field using explicit finite element method

1 Introduction The prediction of broadband near-fault ground motion is an important aspect of seismic risk analysis, and is essential for the evaluation of urban seismic safety. Many methodologies are used to model the near-fault ground motions, such as the Green function method, ?nite element (FE) / ?nite difference (FD) method and a hybrid method (Aagaard, 1999; Oprsal and Zahradnik, 2002; Oprsal et al., 2003 a and b). In the hybrid method, the FE / FD method is used to model the low fr…     

Stochastic earthquake source model for ground motion simulation

In the analysis and design of important structures with relatively long life spans, there is a need to generate strong motion data for possible large events. The source of an earthquake is characterized by the spatial distribution of slip on the fault plane. For future events, this is unknown. In this paper, a stochastic earthquake source model is developed to address this issue. Here, 1D and 2D stochastic models for slip distribution developed by Lavallée et al.(2006) are used. The random field associated with the slip distribution is heavy-tailed stable distribution which can be used for large events. Using 236 past rupture models, the spectral scaling parameter and the four stable or Levy's parameters against empirical relationship for known quantities like magnitude or fault length are developed. The model is validated with data from 411 stations of 1999 Chi-Chi earthquake. The simulated response spectrum showed good agreement to actual data. Further the proposed model is used to generate ground motion for the 1993 Killari Earthquake where strong motion data is not available. The simulated mean peak ground velocity was in turn related to the intensity(MSK) and compared against values in the literature.     

A simplified method for simulation of strong ground motion using finite rupture model of the earthquake source

We present a simplified method to simulate strong ground motion for a realistic representation of a finite earthquake source burried in a layered earth. This method is based on the stochastic simulation method of Boore (Boore, D. M., 1983, Bull. Seism. Soc. Am. 73, 1865–1894) and the Empirical Greens Function (EFG) method of Irikura (Irikura, K., 1986, Proceedings of the 7th Japan Earthquake symposium, pp. 151–156). The rupture responsible for an earthquake is represented by several subfaults. The geometry of subfaults and their number is decided by the similarity relationships. For simulation of ground motion using the stochastic simulation technique we used the shapping window based on the kinetic source model of the rupture plane. The shaping window deepens on the geometry of the earthquake source and the propagation characteristics of the energy released by various subfaults. The division of large fault into small subfaults and the method for accounting their contribution at the surface is identical to the EGF. The shapping window has been modified to take into account the effect of the transmission of energy released form the finite fault at various boundaries of the layered earth model above the source. In the present method we have applied the correction factor to adjust slip time function of small and large earthquakes. The correction factor is used to simulate strong motion records having basic spectral shape of ² source model in broad frequency range. To test this method we have used the strong motion data of the Geiyo earthquake of 24th March 2001, Japan recorded by KiK network. The source of this earthquake is modelled by a simple rectangular rupture of size 24 × 15 km, burried at a depth of 31 km in a multilayered earth model. This rupture plane is divided into 16 rectangular subfaults of size 6.0 × 3.75 km each. Strong motion records at eight selected near-field stations were simulated and compared with the observed records in terms of the acceleration and velocity records and their response spectrum. The comparison confirms the suitability of proposed rupture model responsible for this earthquake and the efficacy of the approach in predicting the strong motion scenario of earthquakes in the subduction zone. Using the same rupture model of the Geiyo earthquake, we compared the simulated records from our and the EGF techniques at one near-field station. The comparison shows that this technique gives records which matches in a wide frequency range and that too from simple and easily accessible parameters of burried rupture.     

震源参数对强地面震动模拟结果的影响

基于运动学震源模型,进行了不同震源参数情形下强地面震动数值模拟.结果表明,不同的破裂过程会产生差别甚大的强地面运动分布,一次确定性震源参数的模拟结果不能作为活动断层地震危害性评价的指标,只有通过大量三维地震动场模拟计算,给出地面震动评估的统计结果,才是比较合理的发展方向.由于一次三维地震动场计算耗时很大,因此解决问题的关键是如何考虑合理的震源参数.     

Velocity structure building and ground motion simulation of the 2014 Ludian Ms 6.5 Earthquake

This study constructs a 3 D velocity structure model of the Ludian region in the Yunnan province, southwestern China, and simulates ground motion propagation of the 2014 Ludian Ms 6.5 earthquake. It aims to construct the local velocity structure of the Ludian region in three dimensions and with high precision. The simulation, using the spectral element method, is validated by field data from the Ludian earthquake records. Thus, it demonstrates that the adopted key parameters, such as the seismic source mechanism, propagation medium and geographical features of the engineering site, are appropriated for the simulation. Meanwhile, the simulation generates the ground motion distribution of the study region with an earthquakeinduced landslide in Ludian earthquake.     

应用动态复合震源模型模拟汶川Mw7.9地震强地面运动

2008年5月12日中国汶川地区发生Mw7.9地震,震中位置103.4°E,31.0°N.主要发震断层空间展布长达300多公里,由南西方向到北东方向呈现明显的分段性,汶川—映秀段逆冲为主兼有少量的右旋走滑分量;安县—北川段为逆冲-右旋走滑的断层错动;青川段以右旋走滑为主兼有少量逆冲分量.采用改进后的复合震源强地面运动预测模型,建立了长为320 km,宽为20 km的断层破裂运动学模型,实现了断层分段、空间倾角、滑动方向连续变化的动态设定.数值模拟结果给出了近断层两侧(上、下盘)的地面加速度的分布特征,并同卧龙、郫县走石山及绵竹清平强震观测记录进行了对比分析.模拟加速度时程曲线无论在波形、持续时间、频率分量、峰值大小同观测记录都具有较好的相似性.利用现有83个已知经纬度台站的强震实测数据及数值模拟的结果同Boore等的新一代衰减关系(NGA)进行比较,对比模拟与实际观测水平峰值加速度的一致程度.近断层峰值加速度分布特征则进一步显示了在汶川、北川和青川附近明显的高值分布区域,同野外地质调查相一致.进一步的分析结果也表明,汶川—映秀段逆冲为主的断层上盘的运动量远大于断层下盘,在距离断层地表出露位置5 km处,峰值加速度N-S、E-W及UP方向分量的比值分别为1.72∶1、2.5∶1及1.77∶1.本文中给出的动态复合震源模型和近断层区域强震模拟的计算方法,对大震强地面运动的预测及实现近实时强地面运动分布特征的圈定(Shaking Map)有着重要的实际意义.     

基于地震动参数的城市建筑物震害模拟——以兰州市城关区为例

首先利用最短断层法烈度衰减模型分别模拟两次地震的地震动参数空间分布,并通过与实际地震的极震区对比,验证该模型模拟地震烈度的可靠性.然后,基于模拟的地震烈度空间分布和建筑物的结构类型、层高等信息,采用结构弹塑性时程分析方法对兰州市城关区建筑物进行三维震害模拟.研究结果表明:最短断层法是一个模拟历史地震烈度空间分布较好的模...     

3-D physical model in strong ground motion numerical simulation： A case study of Kunming basin

Seismic hazard assessment based on urban active faults can provide scientific bases for city planning and projectconstruction,while numerical simulation of strong ground motion is an important method for seismic hazard pre-diction and assessment.A 3-D physical model in conformity with real strata configuration of(mainly)the Quater-nary is a prerequisite to ensure the reliability of the simulation results.In this paper,we give a detailed account ofthe technical scheme and process for creating a 3-D physical model in Kunming basin.The data used are synthe-sized from seismogeological data,borehole data,topographic data,digital elevation mode(DEM)data,seismicexploration results and wave velocity measurements.Stratigraphic division is based mainly on shear wave velocity,with strata sequence taken into consideration.The model construction is finally accomplished with ArcGIS andmany relevant programming techniques via layer-by-layer stacking(in depth direction)of the adjacent mediuminterfaces(meshes).Meanwhile,a database of 3-D physical models is set up,which provides model data and pa-rameters for strong ground motion simulation.Some processing methods and significant issues are also addressedin the paper in accordance with different types of exploration and experimental data.     

强震地面运动的超随机特性研究

简述了几种常用的地震动平稳随机模型，这几种地震动平稳随机模型的功率谱是一组光滑的函数，相应的自相关函数基本上是指数衰减的振荡函数，且很快衰减到零；但是真实地震动的归一化自相关函数则有一较显著的随机噪声项，这个随机噪声的幅值为0．15左右，这就是本文中所说的超随机特性。目前常用的地震动平稳随机模型没有考虑这个随机噪声项及其对结构反应的影响。本文将真实地震动的自相关函数分解为一确定性函数和一随机噪声的叠加，并对自相关函数中的噪声部分进行了分析，得出两条重要性质。本文的研究结果表明地震动加速度时程的平方和(SS)比峰值加速度(PGA)更好地量度了地震地面运动强度。由于归一化自相关函数的随机噪声部分所对应的功率谱的随机波动成分对频率的积分为零，即归一化自相关函数的噪声部分对地震动总功率或平方和的贡献为零，因此自相关函数的随机噪声项对地震动的幅值影响不大，但自相关函数的随机噪声项明显改变了地震动功率谱在频域上的分布特征，因此会对结构反应产生一定的影响。由于篇幅所限详细内容将在下一篇文章中作进一步探讨。     

Estimating coseismic deformations from near source strong motion records: methods and case studies

Digital strong-motion accelerographs have opened up the possibility of extracting ground motion characteristics at much lower frequencies than was offered by analogue instruments. High-quality digital data obtained close to the faults have tempted several efforts to retrieve permanent ground displacements after an earthquake. Such attempts have been partly successful, and somewhat subjective, the main reason being the presence of baseline offsets in the accelerometric data. We review existing methods for such applications, discuss their limitations and propose a more objective and improved scheme to make baseline adjustments and obtain permanent displacements. The proposed technique is applied to 26 digital recordings from the 29 May 2008 Ölfus Earthquake in South Iceland and 9 recordings from the 1999 Chi-Chi, Taiwan, Earthquake, and the permanent displacements obtained are compared with published results and GPS measurements from nearby stations. Our case studies show that the proposed technique, in addition to being simple and objective, is effective in making adjustments for baseline errors in accelerometric data.     

宽频带地震动混合模拟方法综述

从发展现状、 主要研究成果和可探讨问题等方面, 对宽频带地震动混合(hybrid)模拟方法进行了系统的评述． 首先介绍了混合模拟方法的发展历程, 从高频段模拟技术、 低频段模拟技术和宽频带合成技术及交叉频率等方面, 介绍了混合模拟方法的研究现状; 随后介绍了混合模拟方法发展过程中一些关键的改进, 包括随频率变化的辐射因子、 非线性场地放大因子、 多重S-S波散射理论等; 最后, 对混合模拟方法中值得深入研究的问题进行了探讨．      

2015年尼泊尔Mw7.8地震震源机制InSAR反演及强地面运动模拟

2015年4月25日,在尼泊尔中部发生了M_w7.8地震.本文利用ALOS-2和SENTINEL-1A宽幅数据获取了该地震大范围的同震形变场,并反演了该地震断层破裂的几何特征及运动机制,继而以此为约束资料反演地震强地面运动.InSAR结果显示本次地震造成了巨大的地表形变,LOS向最大抬升量达到1.3 m,最大下沉量达到0.7 m.震源机制反演得到的最优的滑动分布模型表明,断层的走向为291°,倾角为7.6°,倾滑主要分布在深度为12~18 km范围,主倾滑分布范围在长度上达到了140 km,该范围内的平均倾滑角为95°.本次地震最大倾滑量达到5.3 m,位于深度15 km处.累计释放地震矩达 6.5×10²⁰N·m,约合矩震级M_w7.8.该地震发生在印度与欧亚板块俯冲逆冲界面之间,发震构造推断为主喜马拉雅逆冲断裂,属于典型的喜马拉雅型——低角度逆断层型强震.以该滑动分布模型参数为基础利用随机振动的有限断层模型进行尼泊尔地震的强地面运动模拟,结果显示最大地震烈度为Ⅸ度,烈度分布的范围及烈度等级与USGS模型结果对比具有很高的符合度.     

Strong motion simulation by the composite source modeling： A case study of 1679 M8.0 Sanhe-Pinggu earthquake

In this study, a composite source model has been used to calculate the realistic strong ground motions in Beijing area, caused by 1679 MS8.0 earthquake in Sanhe-Pinggu. The results could provide us the useful physical parame-ters for the future seismic hazard analysis in this area. Considering the regional geological/geophysical background, we simulated the scenario earthquake with an associated ground motions in the area ranging from 39.3°N to 41.1°N in latitude and from 115.35°E to 117.55°E in longitude. Some of the key factors which could influence the characteristics of strong ground motion have been discussed, and the resultant peak ground acceleration (PGA) distribution and the peak ground velocity (PGV) distribution around Beijing area also have been made as well. A comparison of the simulated result with the results derived from the attenuation relation has been made, and a suf-ficient discussion about the advantages and disadvantages of composite source model also has been given in this study. The numerical results, such as the PGA, PGV, peak ground displacement (PGD), and the three-component time-histories developed for Beijing area, have a potential application in earthquake engineering field and building code design, especially for the evaluation of critical constructions, government decision making and the seismic hazard assessment by financial/insurance companies.     

Earthquake response of a base-isolated bridge subjected to strong near-fault ground motion

The South Iceland Lowland is an active seismic zone. In May 2008 a magnitude 6.3 (M_w) earthquake struck the area. The 370-m-long base-isolated Oseyrar Bridge situated close to the epicentre was hit by strong ground motion. Concrete stoppers at the top of all piers were badly smashed and all four wing walls of the abutments were severely damaged. The study showed that it is possible with numerical models to back-calculate the observed damage based on recorded ground motion in the area. The recorded loads were larger than prescribed by Eurocode 8 for the site even though the magnitude and location of the earthquake was as expected. The main reason was a near-fault pulse which is not covered in the code. The pulse dominated the bridge response and is therefore important to consider. Finally, an improved design is presented that could have prevented the damage.     

Wavelet-Hilbert transform-based simulation of pulse-like ground motion

In nonlinear dynamic structural analysis, a suite of pulse-like ground motions is required for the performance-based design of structures near active faults. The dissimilarity in the amplitude and frequency content of the earthquake time series referred to nonstationary properties in temporal and spectral, respectively. An approach is proposed based on the nonstationary properties of the far-field records and the seismological information in an event for simulating pulse-like records. The pulse-like earthquake time history is estimated via the superposition of the residual part of the earthquake with the estimated pulse. The wavelet-based Hilbert transform is utilized to characterize the nonstationary properties, the instantaneous amplitude, and frequencies of far-field records to model residual part. The effects of near-fault and pulse are estimated based on the seismological properties of the region. The validation of the procedure is indicated by comparing simulated time-series, response spectra, and Arias intensity with recorded pulse-like records in two different earthquakes in California; the M_w 6.7 1994 Northridge and the M_w 6.5 1979 Imperial valley.

     

考虑地形起伏和障碍体破裂的汶川地震强地面运动数值模拟

2008年5月12日四川汶川地区发生M_W7.9地震,震中位置103.4°E,31.06°N.这次地震造成了以汶川、映秀为中心及其周边地域建筑物的严重破坏和人员的重大伤亡,且因为高山等地形复杂区域抢险救灾的艰巨性,为及时救援造成很大干扰.为更好理解地形因素对于强地面数值模拟结果的影响,建立了包含地形起伏影响及去除地形影响的两类模型.同时,依据震源破裂过程运动学反演结果,建立了包含障碍体破裂过程的震源滑动模型,实现断层分段、空间倾角以及滑移角的动态设定.基于动力学的地震动模拟方法,通过对地震波传播过程的数值计算和后处理分析,模拟由地震激发的区域强地面运动过程.结果显示：（1）强震动台站的断层距对地形效应具有放大或抑制作用,距离断层破裂带越近,地形效应越明显,反之,距离越远,则地形效应越微弱;（2）因为地形高差与障碍体的影响,地震造成的峰值可能出现在震中区域之外;（3）考虑地形影响模型的地表峰值速度（PGV）区域位于汶川与北川附近;而未考虑地形影响模型的PGV区域位于灌县—江油断层的后半段,处清平、安县附近;对汶川地震近实时强地面运动波场的模拟、峰值图谱的圈定及未来大地震强地面运动特征的预测都有重要指示意义.

     

随机有限断层法合成地震动的研究与应用

目前很多研究者采用随机有限断层模型预测地震动并被证明是可行的.本文运用随机有限断层地震动叠加合成方法,模拟了1988年肃南5.7级地震,与实际记录进行对比分析,发现：用有限断层方法模拟得到的峰值加速度以及峰值加速度出现所对应的特征时刻与真实记录较为吻合;比较模拟的地震动反应谱和实际记录的加速度反应谱,总体上在工程感兴趣的频段内,有限断层方法拟合的结果基本能满足实际工作的需要.为进一步开拓该方法在工程应用中的前景,以兰州市柴家峡水电站为例,将此理论方法应用于缺乏强震记录地区的近场地震动估计中,模拟分析了马衔山北缘活动断裂发震时在坝址区产生的地震动特征,其近场合成结果与1125年兰州7.0级地震的烈度分布符合较好,可供工程抗震设计参考使用.     

Strong ground motion simulation during the November 1759 Earthquake along Serghaya Fault in the metropolitan of Damascus, Syria

The seismic hazard potential for metropolitan of Damascus, Syria is mainly controlled by earthquakes along Serghaya Fault which is a branch of Dead Sea Fault System. In this study, strong ground motion due to the November 1759 Earthquake along the fault of Serghaya was estimated with a numerical simulation technique. In the simulation, the Kostrov-like slip-velocity function was used as an input to the discrete wave number method to simulate the strong ground motions in a broadband frequency range. In order to model the incoherent rupture propagation which can excite large high-frequency waves, random numbers are added to arrival time of circular rupture front. MMI intensities calculated from the synthetic ground motions are compared with the observed values by Ambraseys and Barazangi (J Geophys Res 94:4007-4013, 1989). The calculated intensities are in good agreement with the observed ones at the most sites that validate appropriateness of the proposed source model. The PGA and PGV in the eastern region of Damascus city are higher than those in the western region due to the effects of local site amplification. The simulated high-frequency (1.0–6.0 Hz) ground motions for the sites in the Damascus city are higher than the design requirements defined by the Syrian building code. Furthermore, the simulated high-frequency ground motions for sites in the focal region are bigger than the design requirements in the case of the near-fault factors and are not considered. That demonstrates the appropriateness of considering the near-fault factors for a site near the focal region as introduced by the new building code.