九寨沟7.0级地震地表地震动位移及静态位移的模拟研究

北京时间2017年8月8日21时19分在四川省阿坝州九寨沟县（北纬33.2°、东经103.8°）发生7.0级地震,给九寨沟景区造成了滑坡坍塌等地质灾害.本文利用Crust1.0资料和反演的震源破裂过程建立了研究区三维介质模型及三维震源模型,采用谱元数值模拟方法模拟了九寨沟近断层地表地震动速度时程,并与强震台站实际速度记录的低频做了对比,两种结果对比的一致性,验证了介质模型及震源模型的有效性.在此基础上近一步模拟了地表位移时间序列,获得了位移峰值PGD及静态位移的空间分布,分析并给出了九寨沟地震地表位移的主要运动特征.     

Effect of viscous,viscoplastic and friction damping on the response of seismic isolated structures

In this paper the efficiency of various dissipative mechanisms to protect structures from pulse‐type and near‐source ground motions is examined. Physically realizable cycloidal pulses are introduced, and their resemblance to recorded near‐source ground motions is illustrated. The study uncovers the coherent component of some near‐source acceleration records, and the shaking potential of these records is examined. It is found that the response of structures with relatively low isolation periods is substantially affected by the high‐frequency fluctuations that override the long duration pulse. Therefore, the concept of seismic isolation is beneficial even for motions that contain a long duration pulse which generates most of the unusually large recorded displacements and velocities. Dissipation forces of the plastic (friction) type are very efficient in reducing displacement demands although occasionally they are responsible for substantial permanent displacements. It is found that the benefits by hysteretic dissipation are nearly indifferent to the level of the yield displacement of the hysteretic mechanism and that they depend primarily on the level of the plastic (friction) force. The study concludes that a combination of relatively low friction and viscous forces is attractive since base displacements are substantially reduced without appreciably increasing base shears and superstructure accelerations. Copyright © 2000 John Wiley & Sons, Ltd.     

Maximum seismic displacements evaluation of steel frames from their post-earthquake residual deformation

The maximum seismic displacements of a structure can be used for the assessment of its post-earthquake performance. In this paper, a simple and efficient procedure is proposed for determining maximum seismic displacements of planar steel frames from their residual deformation. More specifically, the inelastic behaviour of 36 moment resisting steel frames and 36 concentrically X-braced steel frames under one hundred strong ground motions is investigated. Thus, on the basis of extensive parametric studies for these structures and seismic records, empirical equations are constructed for simple and effective prediction of maximum seismic displacements from residual deformation, which can be measured in-situ after strong seismic events. It is found that the usage of residual deformation can be effectively utilized to evaluate the post-earthquake performance level of steel structures.     

Ground motion near an expanding preexisting crack

We present a study of the motion of the ground in the near field of a preexisting vertical crack driven by excess tensile stress. Using the discrete wave number method, we make a complete representation of the three components of ground displacement resulting from a small incremental extension of the bottom tip of the crack and analyze the effects of the medium structure on the ground response. The results show the strong impulsive character of the dynamic motion near the source and demonstrate that the first motion is directed everywhere outward. Marked oscillations are observed in the ground response associated with the ringing of the crack faces triggered by the rupture. The displacement is dominantly vertical near the epicenter but becomes predominantly horizontal beyond the immediate source region. The presence of layers has a strong effect on the complexity and duration of the ground response. The static vertical and longitudinal displacements are respectively downward and inward in the epicentral area.     

Estimation of maximum mass velocities in the focal zones of strong earthquakes based on measured displacements of rock blocks: A case study of Kyrgyzstan

An important task in seismic hazard assessment is estimation of the intensity and frequency of extremely strong earthquake effects, in particular, peak ground velocities (PGV). Earlier, a method was proposed to evaluate PGV values based on the magnitude of displacements of rock blocks (Rodkin et al., 2012). In this study, this method is used to analyze field data on the source zones of the August 19, 1992, M_S = 7.3 Susamyr earthquake and the January 3, 1911, M_w = 7.9 Kemin earthquake, and estimate maximum ground shaking at the upper construction site of the Upper Naryn series of hydropower plants, Kyrgyz Republic. It is shown that the resulting estimates are consistent with data obtained through other techniques. Therefore, the new approach can be recommended to estimate earthquake effects.     

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.     

Scaling of residual displacements in terms of elastic and inelastic spectral displacements for existing SDOF systems

Structures undergoing inelastic displacements during earthquake ground motions are known to sustain some amount of residual displacements, which may make them unusable or unsafe. In this study an attempt is made to estimate residual displacements for elastic-perfectly-plastic single-degree-of-freedom oscillators with a given lateral strength ratio. It is observed in the case of a class of ground motions that there are no trends in the dependence of residual displacement on the temporal features of the ground motion, and thus any estimation of residual displacements should be carried out only in the statistical sense. Statistical estimation of residual displacement spectrum via normalization with respect to inelastic or elastic spectral displacements is considered, and it is found that normalization with respect to inelastic spectral displacements is preferable. Expressions for residual displacement spectra are proposed for both types of normalizations and for the givenlateral-strength-ratio type oscillators.     

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.     

Response of sliding structures to earthquake support motion

To study the effectiveness of sliding supports in isolating structures from damaging earthquake ground motions, a mathematical model of a single degree of freedom structure supported on a sliding foundation and subjected to the N-S component of the El Centro 1940 earthquake is considered. Spectra for absolute accelerations, relative displacements, relative-to-ground displacements, sliding displacements and residual sliding displacements are evaluated for three mass ratios, four coefficients of friction and a damping of 5 per cent critical. It is observed that, for structures with periods less than 1-8 s, for the coefficients of friction considered, the suprema of relative-to-ground displacements, sliding displacements and residual sliding displacements are only of the order of 1–25 times the peak ground displacement. To study the response sensitivities, the spectra for absolute acceleration and sliding displacement of the 1949 Olympia earthquake (S86E component) are also presented. It is concluded that sliding supports can be quite effective in isolating structures from support excitations.     

Coseismic displacement estimate of the 2013 M_S7.0 Lushan,China earthquake based on the simulation of near-fault displacement field

Usually, GPS observation provides direct evidence to estimate coseismic displacement. However, GPS stations are scattered, sparse and cannot provide a detailed distribution of coseismic displacement. Strong ground motion records share the same disadvantages as GPS in estimating coseismic displacement. Estimations from In SAR data can provide displacement distributions; however, the resolution of such methods is limited by the analysis techniques. The paper focuses on estimating the coseismic displacement of the M_S7.0 Lushan earthquake on April 20, 2013 using a simulation of the wave field based on the elastic wave equation instead of a quasi-static equation. First, the media and source models were constructed by comparing the simulated velocity and the record velocity of the ground motion. Then simulated static displacements were compared with GPS records. Their agreement validates our results. Careful analysis of the distribution of simulated coseismic displacements near the fault reveals more details of the ground motion. For example, an uplift appears on the hanging wall of the fault,rotation is associated with the horizontal displacement, the fault strike and earthquake epicenter provide the main control on motion near the faults, and the motion on the hanging wall is stronger than that on the footwall. These results reveal additional characteristics of the ground motion of the Lushan earthquake.     

Ground deformation modeling of flank dynamics prior to the 2002 eruption of Mt. Etna

On 22 September 2002, 1 month before the beginning of the flank eruption on the NE Rift, an M-3.7 earthquake struck the northeastern part of Mt. Etna, on the westernmost part of the Pernicana fault. In order to investigate the ground deformation pattern associated with this event, a multi-disciplinary approach is presented here. Just after the earthquake, specific GPS surveys were carried out on two small sub-networks, aimed at monitoring the eastern part of the Pernicana fault, and some baselines belonging to the northeastern EDM monitoring network of Mt. Etna were measured. The leveling route on the northeastern flank of the volcano was also surveyed. Furthermore, an investigation using SAR interferometry was performed and also the continuous tilt data recorded at a high precision sensor close to the epicenter were analyzed to constrain the coseismic deformation. The results of the geodetic surveys show a ground deformation pattern that affects the entire northeastern flank of the volcano, clearly shaped by the Pernicana fault, but too strong and wide to be related only to an M-3.7 earthquake. Leveling and DInSAR data highlight a local strong subsidence, up to 7 cm, close to the Pernicana fault. Significant displacements, up to 2 cm, were also detected on the upper part of the NE Rift and in the summit craters area, while the displacements decrease at lower altitude, suggesting that the dislocation did not continue further eastward. Three-dimensional GPS data inversions have been attempted in order to model the ground deformation source and its relationship with the volcano plumbing system. The model has also been constrained by vertical displacements measured by the leveling survey and by the deformation map obtained by SAR interferometry.     

区域网GPS观测得到的汶川大地震前后的地壳垂直运动

中国地壳运动观测网络1000个观测站的GPS非连续观测区域网分别在1999年、 2001年、 2004年、 2007年和2009年作了5次观测。 2008年5月12日汶川8.0 级地震震中(31.0°N, 103.4°E)恰好在区域网GPS观测站密集的地区。 区域网长期、 多期GPS观测可降低年周期变化影响, 有利于获取此次地震前后的垂直位移趋势变化。 简要讨论了GPS垂直位移观测的精度。 分析了垂直位移观测的主要干扰地面沉降, 特别是华北地区因大量抽取地下水产生的严重地面沉降。 为获取汶川地震前垂直运动信息, 首先剔除因大量抽取地下水产生的大幅度沉降干扰结果, 通过趋势面分析中国大陆垂直位移空间分布, 显示了3个垂直位移沉降最显著区域。 对比分析表明, 临近汶川震区的沉降区, 未见大量抽取地下水干扰影响。 汶川地震前1999—2007年区域网GPS观测站得到的垂直位移表明, 汶川地震紧临显著沉降区的西北侧, 龙门山断层北段垂直运动闭锁。 该沉降区与另两个沉降区的时空变化明显不同, 也与区域网水平应变异常区的空间分布不同, 但该沉降区与区域网水平应变异常区同时出现。 大幅度同震垂直位移集中在龙门山断层北段震前垂直位移闭锁区。 这些事实表明, 汶川地震前GPS观测到的紧临震中的沉降区及垂直运动闭锁区与汶川地震的发生存在密切关系。     

Coseismic displacement estimate of the 2013 <Emphasis Type="Italic">M</Emphasis><Subscript>S</Subscript>7.0 Lushan,China earthquake based on the simulation of near-fault displacement field

Usually, GPS observation provides direct evidence to estimate coseismic displacement. However, GPS stations are scattered, sparse and cannot provide a detailed distribution of coseismic displacement. Strong ground motion records share the same disadvantages as GPS in estimating coseismic displacement. Estimations from InSAR data can provide displacement distributions; however, the resolution of such methods is limited by the analysis techniques. The paper focuses on estimating the coseismic displacement of the M _S7.0 Lushan earthquake on April 20, 2013 using a simulation of the wave field based on the elastic wave equation instead of a quasi-static equation. First, the media and source models were constructed by comparing the simulated velocity and the record velocity of the ground motion. Then simulated static displacements were compared with GPS records. Their agreement validates our results. Careful analysis of the distribution of simulated coseismic displacements near the fault reveals more details of the ground motion. For example, an uplift appears on the hanging wall of the fault, rotation is associated with the horizontal displacement, the fault strike and earthquake epicenter provide the main control on motion near the faults, and the motion on the hanging wall is stronger than that on the footwall. These results reveal additional characteristics of the ground motion of the Lushan earthquake.     

单自由度体系的地震残余变形研究

结构在经受地震动作用后会发生变形和位移,其中在震动结束后不能恢复的这一部分,即为残余变形或永久变形。残余变形取决于结构本身的动力性能和输入地震波的特性以及场地条件等。残余变形能够提供震害评估的信息,同时也是震后加固修复的指标。对单自由度体系进行了研究,考察不同自振周期、阻尼比、延性水准、滞回特性以及输入地震动下的残余变形,得到其影响因素并分析其中机理,为以最大变形和累积耗能为依据的基于性能的抗震工程学提供了补充和新的思路。     

Modelling gravity variations consistent with ground deformation in the Campi Flegrei caldera (Italy)

In recent years (1970–72 and 1982–84) two inflation episodes took place in the Campi Flegrei caldera (Italy), characterized by significant ground uplift and gravity variations. An elastic half-space model with vertical density stratification is employed to compute the displacement field and the gravity variations produced by the deformation of buried layers, following the inflation of a spherically symmetric deformation source. Contributions to gravity variations are produced by dilation/contraction of the medium, by the displacements of density interfaces (the free surface and subsurface layers) and of source boundaries and, possibly, by new mass input from remote distances into the source volume. Three cases were examined in detail: In case I, the magma chamber is identified as the deformation source and volume and pressure increase in the magma chamber is due to input of new magma from remote distances; in case II deformation is due to magma differentiation within the magma chamber (deformation source with constant mass); in case III the geothermal system is identified as the deformation source and a pressure increase, possibly driven by the exsolution of high temperature and high pressure volatiles in the magma chamber, is assumed to play a dominant role. From the comparison between measured and computed gravity residuals (free-air-corrected gravity variations) we can assess that, in case I, an inflation source with constant density would predict gravity residuals compatible with observations, whereas an expansion at constant mass (case II) would predict gravity residuals much lower than observed. The resolving power of gravity data however prevents accurate assessment of the density of the emplaced material. In case III, the pervasive density increase of the geothermal fluids induced by pressure increase is assumed to be the main source of gravity variations. The average porosity value required for this model to match both the ground deformation and the gravity residuals is found to be ˜10%, a value which is compatible with measured porosity values at Campi Flegrei in deep wells. The subsidence phases following both inflation episodes and the gravity residuals during subsidence lead us to consider case III as more plausible, even if a suitable combination of cases I and III cannot be discarded.     

Physically compliant,conditionally simulated spatially variable seismic ground motions for performance‐based design

The performance‐based design of lifeline systems requires spatially variable seismic excitations at the structures' supports that are consistent with prescribed seismic ground motion characteristics and an appropriate spatial variability model—such motions can be obtained through conditional simulation. This work revisits the concept of conditional simulation and critically examines the conformity of the generated motions with the characteristics of the target random field and observations from data recorded at dense instrument arrays. Baseline adjustment processing techniques for recorded earthquake accelerograms are extended to fit the requirements of simulated and conditionally simulated spatially variable ground motions. Emphasis is placed on the use of causal vs acausal filtering in the data processing. Acceleration, velocity and displacement time histories are evaluated in two example applications of the approach. The first application deals with a prescribed synthetic time history that incorporates nonstationarity in the amplitude and frequency content of the motions and depends on earthquake magnitude, source–site distance and local soil conditions; this example results in zero residual displacements. The second application considers as prescribed time history a recording in the vicinity of a fault and yields nonzero residual displacements. It is shown that the conditionally simulated time histories preserve the characteristics of the prescribed ones and are consistent with the target random field. The results of this analysis suggest that the presented methodology provides a useful tool for the generation of spatially variable ground motions to be used in the performance‐based design of lifeline systems. Copyright © 2006 John Wiley & Sons, Ltd.     

福州盆地强地面运动特征的有限元数值模拟

区域性地震波强地面运动的量化数值模拟分析结果可以用来指导城市规划建设,并在防震减灾中发挥重要作用. 本文采用有限元数值模拟方法来模拟由地震激发的区域地震波强地面运动过程,并得到地表峰值速度和加速度的分布特征.考虑到福州是东南沿海的重要省会城市,其明显的盆地结构特征使它很容易遭受强地震灾害的影响. 因此本文以福州盆地为主要研究对象,假定盆地的主要断层某一位置在未来可能发生灾害性地震,则该地震会激发地震波的强地面运动,并由于地形、沉积层等主要影响,在盆地内部发生放大.通过对地震波传播过程的数值模拟和后处理分析,给出了该盆地的地表峰值位移、峰值速度和峰值加速度分布图谱.该图谱可为未来的福州城市规划和抗震减灾提供定量科学参考依据.     

Development of seismic fragility curves for low-rise masonry infilled reinforced concrete buildings by a coefficient-based method

This study presents a seismic fragility analysis and ultimate spectral displacement assessment of regular low-rise masonry infilled (MI) reinforced concrete (RC) buildings using a coefficient-based method. The coefficient-based method does not require a complicated finite element analysis; instead, it is a simplified procedure for assessing the spectral acceleration and displacement of buildings subjected to earthquakes. A regression analysis was first performed to obtain the best-fitting equations for the inter-story drift ratio (IDR) and period shift factor of low-rise MI RC buildings in response to the peak ground acceleration of earthquakes using published results obtained from shaking table tests. Both spectral acceleration-and spectral displacement-based fragility curves under various damage states (in terms of IDR) were then constructed using the coefficient-based method. Finally, the spectral displacements of low-rise MI RC buildings at the ultimate (or near-collapse) state obtained from this paper and the literature were compared. The simulation results indicate that the fragility curves obtained from this study and other previous work correspond well. Furthermore, most of the spectral displacements of low-rise MI RC buildings at the ultimate state from the literature fall within the bounded spectral displacements predicted by the coefficient-based method.     

Parametric investigation of lateral spreading of gently sloping liquefied ground

This paper investigates the main parameters affecting the anticipated maximum surface displacements due to earthquake-induced lateral spreading of mildly sloping ground. The main tool used for this purpose is a numerical methodology employing a bounding surface plasticity model implemented in a finite difference code, which has been thoroughly validated against 16 published centrifuge lateral spreading experiments. This study shows that important problem parameters are the mean ground (surface) acceleration, the duration of strong shaking following the onset of liquefaction, the corrected SPT blowcount, the depth to the sliding plane, the inclination of the ground surface and the fines content of the liquefied soil layers. A new approximate multi-variable relation is proposed for the estimation of ground surface displacements due to lateral spreading in gently sloping ground, which includes the foregoing parameters. The form of the relation builds upon sliding block theory, but its final formulation is based on statistical analysis of the input data and the results from 120 parametric analyses performed with the validated numerical methodology. Comparison of the predictions of the proposed relation for ground surface displacement against pertinent field data (from 256 case histories) and centrifuge test measurements shows satisfactory accuracy. Furthermore, the variation of lateral displacements with depth is explored and distinct displacement patterns are proposed for uniform, 2-layer and 4-layer ground profiles.     

半空间异质隆起的出平面动力响应:地表运动

采用闭合解析解对水平地表圆形非匀质隆起出平面运动特征进行详细分析。结果表明：（1）隆起区域介质软硬程度对其出平面地表运动影响非常大，软质隆起表面的地表位移较匀质隆起情况有显著放大，地表运动波动效应明显增强，而硬质隆起则减弱地表运动；（2）软质隆起地表位移幅值最大反应和平均反应增大的程度一般来说至少不低于隆起区域波速降低的程度，很多情况是远大于波速降低的程度，但最大反应出现的位置和频段主要受入射波角度控制；（3）当波垂直传播时，地表位移放大出现在隆起顶部，频率随隆起区变软，明显向低频移动，可出现在很低频段内，且随隆起区变软放大更为显著；（4）当波掠入射时，地表最大位移出现在隆起后表面，地表运动仍然十分强烈，甚至比波垂直入射时隆起顶部反应还要大，但出现在较高频段内。