Seismic ground motion relationships in southern China based on stochastic finite-fault model

The characteristics of seismic ground motions in southern China are difficult to determine statistically due to a lack of strong ground motion data. In this study, a stochastic finite-fault ground motion model was adopted to simulate the seismic ground motions at bedrock for southern China, based on parameters derived from small and medium earthquakes that have occurred in the region. From these, the response spectra was estimated. A set of ground motion attenuation relationships was then developed based on simulated peak ground motions and response spectral parameters through regression, which would be applicable for use in engineering practice. Through comparisons, it was demonstrated that the proposed ground motion relationships are generally consistent with those obtained from other reported ground motion attenuation models for southern China.     

3D finite-difference simulations of strong ground motions in the Yanhuai area, Beijing, China during the 1720 Shacheng earthquake (Ms 7.0) using a stochastic finite-fault model

Three-dimensional finite-difference (3D-FD) simulations of earthquake wave propagations in the Yanhuai area were performed for the 1720 Shacheng earthquake (M_s 7.0) using a stochastic finite-fault model, running on a parallel supercomputer Hitachi-SR8000 (http://www.lrz-muenchen.de). A stochastic finite-fault model was implemented into the 3D-FD program. The basic idea of the stochastic finite-fault model is that the fault plane can be subdivided into several subfaults (or elements, sources). Radiation from a large earthquake is the sum of contributions from all subfaults with proper time delays, each of which acts as a small independent double-couple point source. Heterogeneity of the fault rupture process was modeled by randomizing the location of initial rupture (hypocenter), slip vectors (slip, rake), and rise-times of subfaults in this study. A 3D velocity model of the Yanhuai area was constructed based on studies that analyzed available geological and geophysical information. A grid increment of 75 m in three directions was used in the 3D-FD simulation, which made it possible to capture the short period information with a resolution as low as 0.5 s in sediment regions. The uncertainties of simulated results caused by the stochastic finite-fault model were studied with a homogeneous 3D model. We found that the effects of the randomness of source on simulated ground motions are only limited in near-fault-region including the surface exposure of the fault and its vicinities, which occupies about 5% of the whole study area. This article presents an integrated approach for simulating the strong ground motions for engineering purpose using the 3D-FD method. Such simulations would be useful for hazard mapping, land using planning, insurance rate assessment, particularly in planning, preparedness, and coordinating emergency response, which must be based on realistic situations induced by concrete (historic or scenario) earthquakes.     

Calibration of stochastic finite-fault ground motion simulations for the 1997 Umbria-Marche, Central Italy, earthquake sequence

The recent 1997 Umbria-Marche, Central Italy, earthquake sequence allowed us to model recorded ground motions using a method developed by Beresnev and Atkinson [Bull Seism Soc Am 87 (1997) 67–84; Seism Res Lett, 69 (1998) 27–32; Bull Seism Soc Am 88 (1998) 1392–1401]. The method generalizes the stochastic ground-motion simulation technique, developed for point sources, to the case of finite faults. It subdivides the fault plane into subfaults and assumes each subfault to be a point source with a ω² spectrum. Geometric spreading and regional anelastic attenuation are included in the model. The data include horizontal acceleration recordings from the SSN and ENEL databases of the 1997 Umbria-Marche events on 26 September, at 00:33 GMT, with M_w=5.7, and at 09:40 GMT, with M_w=6.0; and on 14 October at 15:23 GMT, with M_w=5.6. The strong motion simulations are performed using model parameters based on the results of previous studies, and adjusting the subfault size to calibrate the simulation model against recorded ground motions. Local site response is considered to account for observed amplification effects at specific recording sites (e.g. Nocera Umbra). A good agreement is found between the simulated response spectra and the recorded data, concluding that this method reproduces the salient ground-motion characteristics at different distances and azimuths.     

Study on simulating strong ground motion by fractal stochastic method

The time history of strong ground motion can be synthesized by empirical Green's function (EGF) method.Firstly a large seismic event is discretized into a series of subevents; secondly recordings of earthquakes with proper size and spatial distribution are chosen as time history (EGF) of those subevents; finally the EGFs are summated to get the time history of ground motion caused by the large event.     

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 for the 2013 Lushan M_W6.6 earthquake,Sichuan, China,based on the inverted and synthetic slip models

It is well known that quantitative estimation of slip distributions on fault plane is one of the most important issues for earthquake source inversion related to the fault rupture process. The characteristics of slip distribution on the main fault play a fundamental role to control strong ground motion pattern. A large amount of works have also suggested that variable slip models inverted from longer period ground motion recordings are relevant for the prediction of higher frequency ground motions. Zhang et al. （Chin J Geophys 56：1412-1417, 2013） and Wang et al. （Chin J Geophys 56：1408-1411,2013） published their source inversions for the fault rupturing process soon after the April 20, 2013 Lushan earthquake in Sichuan, China. In this study, first, we synthesize two forward source slip models： the value of maximum slip, fault dimension, size, and dimension of major asperities, and comer wave number obtained from Wang＇s model is adopted to constrain the gen- eration of k-2 model and crack model. Next, both inverted and synthetic slip models are employed to simulate the ground motions for the Lushan earthquake based on the stochastic finite-fault method. In addition, for a comparison purpose, a stochastic slip model and another k-2 model （k 2 model II） with 2 times value of comer wave number of the original k-2 model （k 2 model I） are also employed for simulation for Lushan event. The simulated results characterized by Modified Mer- calli Intensity （MMI） show that the source slip models based on the inverted and synthetic slip distributions could capture many basic features associated with the ground motion patterns. Moreover, the simulated MMI distributions reflect the rupture directivity effect and the influence of the shallow velocity structure well. On the other hand, the simulated MMI bystochastic slip model and k 2 model II is apparently higher than observed intensity. By contrast, our simulation results show that the higher frequency ground motion is sensitive to the degree of sli     

Seismic hazard analysis for engineering sites based on the stochastic finite-fault method

Seismic hazard analyses are mainly performed using either deterministic or probabilistic methods. However, there are still some defects in these statistical model-based approaches for regional seismic risk assessment affected by the near-field of large earthquakes. Therefore, we established a deterministic seismic hazard analysis method that can characterize the entire process of ground motion propagation based on stochastic finite-fault simulation, and we chose the site of the Xiluodu dam to demonstrate the method. This method can characterize earthquake source properties more realistically than other methods and consider factors such as the path and site attenuation of seismic waves. It also has high computational efficiency and is convenient for engineering applications. We first analyzed the complexity of seismogenic structures in the Xiluodu dam site area, and then an evaluation system for ground motion parameters that considers various uncertainties is constructed based on a stochastic finite-fault simulation. Finally, we assessed the seismic hazard of the dam site area comprehensively. The proposed method was able to take into account the complexity of the seismogenic structures affecting the dam site and provide multi-level parameter evaluation results corresponding to different risk levels. These results can be used to construct a dam safety assessment system of an earthquake in advance that provides technical support for rapidly and accurately assessing the post-earthquake damage state of a dam, thus determining the influence of an earthquake on dam safety and mitigating the risk of potential secondary disasters.     

A stochastic model of the Fourier phase of strong ground motion

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1999年台湾集集大地震强地面运动的模拟

利用有限断层模型对1999年台湾集集大地震所产生的近场强地面运动进行了数值模拟,尝试了将具有明确物理意义的震源动力模型的研究结果应用于描述震源过程。计算结果显示,基岩台或接近工程基岩台的计算模拟记录同观测记录符合得很好。进一步研究表明,当综合考虑场地效应对地震动影响时,模拟计算结果得到了明显的改善,同实际观测记录更为相符。本文的研究结果说明,为了科学合理地预测大地震所产生的强地面运动,应综合考虑影响地震所产生的地面运动的"三要素",即:震源过程、传播路径及场地效应。     

Dynamic corner frequency in source spectral model for stochastic synthesis of ground motion

The static corner frequency and dynamic corner frequency in stochastic synthesis of ground motion from finite-fault modeling are introduced, and conceptual disadvantages of the two are discussed in this paper. Furthermore, the non-uniform radiation of seismic wave on the fault plane, as well as the trend of the larger rupture area, the lower corner frequency, can be described by the source spectral model developed by the authors. A new dynamic corner frequency can be developed directly from the model. The d...     

基于强度和能量控制的随机地震动模型

考虑地震动的随机性和频率与强度非平稳性,通过理论分析,提出了一般随机地震动模型,并给出了确定模型参数的原则和方法。该模型以地震动强度、地震动能量以及地震动持时等宏观指标作为控制随机地震动模型参数的指标,而对其内在的频谱组成等指标只要求满足一般地震动的特征。该模型可以用于描述平稳随机过程、强度非平稳随机过程以及强度和频率完全非平稳随机过程。通过与常用功率谱模型的比较,验证了该模型的合理性。     

Vertical coherency function model of spatial ground motion

Many studies have focused on horizontal ground motion, resulting in many coherency functions for horizontal ground motion while neglecting related problems arising from vertical ground motion. However, seismic events have demonstrated that the vertical components of ground motion sometimes govern the ultimate failure of structures. In this paper, a vertical coherency function model of spatial ground motion is proposed based on the Hao model and SMART 1 array records, and the validity of the model is demonstrated. The vertical coherency function model of spatial ground motion is also compared with the horizontal coherency function model, indicating that neither model exhibits isotropic characteristics. The value of the vertical coherency function has little correlation with that of the horizontal coherency function. However, the coherence of the vertical ground motion between a pair of stations decreases with their projection distance and the frequency of the ground motion. When the projection distance in the wave direction is greater than 800 meters, the coherency between the two points can be neglected.     

Kriging metamodeling in seismic risk assessment based on stochastic ground motion models

An efficient computational framework is presented for seismic risk assessment within a modeling approach that utilizes stochastic ground motion models to describe the seismic hazard. The framework is based on the use of a kriging surrogate model (metamodel) to provide an approximate relationship between the structural response and the structural and ground motion parameters that are considered as uncertain. The stochastic character of the excitation is addressed by assuming that under the influence of the white noise (used within the ground motion model) the response follows a lognormal distribution. Once the surrogate model is established, a task that involves the formulation of an initial database to inform the metamodel development, it is then directly used for all response evaluations required to estimate seismic risk. The model prediction error stemming from the metamodel is directly incorporated within the seismic risk quantification and assessment, whereas an adaptive approach is developed to refine the database that informs the metamodel development. The ability to efficiently obtain derivative information through the kriging metamodel and its utility for various tasks within the probabilistic seismic risk assessment is also discussed. As an illustrative example, the assessment of seismic risk for a benchmark four‐story concrete office building is presented. The potential that ground motions include near‐fault characteristics is explicitly addressed within the context of this example. The implementation of the framework for the same structure equipped with fluid viscous dampers is also demonstrated. Copyright © 2015 John Wiley & Sons, Ltd.     

Stochastic strong ground motion simulations in sparsely-monitored regions: A validation and sensitivity study on the 13 March 1992 Erzincan (Turkey) earthquake

Stochastic simulations have recently become quite popular for estimating synthetic ground motion time histories. For seismically active regions that are not well-monitored or studied extensively, input parameters of the simulations should be carefully selected as the reliability of the simulation results directly depends on the accuracy of the input parameters. In the first part of this study, 13 March 1992 Erzincan (eastern Turkey) earthquake (Mw=6.6), which is recorded at only three strong ground motion stations, is simulated using the stochastic finite-fault method. The source and regional path parameters for this event are adopted from previously validated studies whereas the local site parameters are derived herein. In the second part of the paper, sensitivity of the simulation results with respect to small changes in selected input seismic parameters is investigated. The parameters for which sensitivities are computed include stress drop, crustal shear-wave quality factor and kappa operator. A change of 20% in stress drop value results in 14% change in PGA, whereas a 20% difference in the Q₀ value causes 17% change in PGA, and a 20% variation in kappa leads to 15% difference in PGA. Numerical experiments presented in this study prove that the ground motion simulations are prone to trade-off between the source, path and site filters. Hence, input models must be implemented carefully for reliable synthetic ground motions.     

基于物理的随机地震动模型研究

基于物理联系研究地震动随机性,建立了随机地震动与基底输入傅氏谱、场地固有圆频率和场地等价阻尼比之间的物理关系,从随机傅氏谱函数角度描述了地震动随机过程的随机性本质。结合Ⅳ类工程场地的实测地震动记录资料,由数值方法识别了给出基本随机变量的概率分布参数。与实测记录对比表明,本文建立的随机地震动模型具有明确的物理概念,可充分反映地震动的变异性特征。     

Advances in ground motion studies in China

This paper briefly summarizes the works in the processing of strong ground motion data, the factors affecting strong ground motion, the modeling of strong ground motion and the calculating of broad-band response spectrum which have been done recent years by engineering seismologists and seismologists of China. In addition, we think back to the international cooperation in strong ground motion of the recent years and make some expectations for the future.     

基于GP14.3运动学混合震源模型和SPECFEM 3D谱元法的宽频地震动模拟

基于确定性物理模型的全过程地震动模拟是现代地震工程的重要发展方向.然而受限于合理震源模型和计算资源需求,目前模拟的有效频率还多处于低频范围,难以满足工程结构敏感频带（5~10 Hz或更高）需求.本文即借助运动学混合震源模型能激发宽频地震波和谱元法空间高精度及计算收敛快的优势,首先将确定性的凹凸体震源模型与GP14.3随机震源模型结合得到有限断层运动学混合震源模型,进而将上述混合震源模型开发到SPECFEM 3D谱元法开源代码中,实现了基于谱元法和运动学混合震源模型的全过程宽频带地震动模拟.将方法首先应用于一维波速结构模型0~10 Hz地震动模拟,通过与频率波数域（FK）方法结果进行比较,验证了方法的精度;进而应用于2021年5月21日云南漾濞6.4级地震0.1~5 Hz地震动模拟,通过与4个台站的时程记录和相应反应谱的比较,以及与NGA-West2地震动衰减方程在频率0.1~5 Hz的反应谱的比较,检验了方法的适用性;最后给出了漾濞地区的地震动峰值加速度（PGA）和峰值速度（PGV）云图,分析了漾濞地震下近场强地面运动的空间分布特征.结果显示,震中PGA接近400 cm·s^-2,PGV达到45 cm·s^-1,烈度达到Ⅸ度,且受局部地形起伏影响,大理以及洱海西侧位置出现高烈度异常区.

     

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.