共查询到20条相似文献，搜索用时 375 毫秒
1.
Experimental determination of Rayleigh-wave mode velocities using the method of wave number analysis
A method is presented to determine experimentally phase and group velocity dispersion curves of propagating Rayleigh-wave modes. Through the application of the Fourier transform method wave number spectra of surface displacements due to wave propagation along a line are constructed. The dominant peaks in the wave number spectra together with their corresponding wave numbers are identified. From the latter the phase velocities, which correspond to the wave modes present, are calculated. The phase and group velocity dispersion curves of wave modes are determined from repeated experiments with different frequencies of excitation. This method to determine the frequency-dependent Rayleighwave velocities solves the problem of non-linear phase changes between surface points in contrast to the conventional phase difference methods which assume linear phase changes. 相似文献
2.
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. 相似文献
3.
虽然InSAR技术具有高精度、大范围和高空间分辨率等优点,但只能监测雷达视线方向上的一维地表形变;而GPS技术虽可以监测地表的三维形变,但其空间分辨率很低.本文针对融合InSAR和GPS技术监测地表高空间分辨率三维形变展开研究.首先证明了简单的局部最优化迭代算法就能求得综合InSAR和GPS监测地表形变速率的能量函数模型的全局最优估值.随后提出了利用BFGS局部最优算法反演最优的地表三维形变速率.该方法既能避免全局最优化算法计算复杂且难以收敛的问题,又能克服传统的解析法中数值计算不稳定的缺点.最后,通过模拟实验和美国南加州真实数据实验表明,该方法能够得到高精度的地表三维形变速率场.而且当观测或插值误差导致解析法误差较大时,BFGS方法仍能得到高精度、稳定的全局最优解. 相似文献
4.
《Soil Dynamics and Earthquake Engineering》2000,20(1-4)
The paper deals with an application of neural networks for detection of natural periods of vibrations of prefabricated, medium height buildings. The neural network technique is also used to simulate the dynamic response at selected floor of one of the analysed buildings subject to seismic loading induced by explosives in a nearby quarry. Both the training and testing patterns were formulated on the basis of measurements performed on actual structures. The results of neural network identification of natural periods of the considered buildings obtained with different soil, geometrical and stiffness parameters are compared with the results of experiments. The application of back-propagation neural networks enables us to identify the natural periods of the buildings with accuracy quite satisfactory for engineering practice. The experimental and generated data of vibration displacements are compared and much clearer comparison is given on the phase plane: displacements versus velocities. It was stated that a good generalization takes place both with respect to displacements and velocities. 相似文献
5.
行波效应对大跨度空间结构随机地震响应的影响 总被引：1，自引：0，他引：1
深入研究了行波效应对大跨度空间结构随机地震响应的影响,进一步完善了大跨度空间结构随机地震响应分析理论。推导了双支座、单自由度体系地震响应功率谱密度函数的解析表达式,研究了不同频率体系的响应峰值随地面视波速的变化规律,分析了多支撑点、多自由度体系的地震响应功率谱矩阵的特点,发现多自由度体系地震响应随地面视波速的变化规律与单自由度体系相似。数值模拟了某体育馆网壳结构在不同地面视波速情况下的随机地震响应,结果表明,考虑地震动行波效应后,结构地震响应随地面视波速的变化而显著变化,当视波速较低时其变化规律很复杂;且支撑点附近、受拟静力位移影响较大的部分杆件的地震响应明显增大,远离支撑点处、受拟静力位移影响较小的部分杆件的地震响应稍有减小。由此得出结论,对于大跨度空间结构的随机地震响应分析,必须考虑地震动的行波效应,尤其当受拟静力位移影响较大的部分杆件对结构抗震设计起控制作用时;且应对可能出现的地面视波速进行全面分析,作为结构抗震设计依据。 相似文献
6.
A brief review of proposed correlations between peak accelerations and earthquake magnitude and distance has been presented. It has been found that most investigators agree favourably on what should be the amplitude of peak accelerations for the distance range between about 20 and 200 km. For distances less than 20 km, there is significant disagreement in the predicted peak amplitudes, reflecting the lack of data there and the uncertainties associated with the extrapolation. Correlations of peak accelerations, peak velocities and peak displacements with earthquake magnitude, epicentral distance and the geologic conditions of the recording sites have been presented for 187 accelerograms recorded during 57 earthquakes. This data set describes strong earthquake ground motion in the Western United States during the period from 1933 to 1971. For large earthquakes, dependence of peak acceleration, velocity and displacement amplitudes on earthquake magnitude seems to be lost. This suggests that the amplitudes of strong ground motion close to a fault are scaled primarily by the maximum dislocation amplitudes and the stress drop, rather than the overall ‘size’ of an earthquake as measured by magnitude. The influence of geologic conditions at the recording station seems to be of minor importance for scaling peak accelerations, but it becomes noticeable for the peaks of velocity and even more apparent for the peaks of displacement. 相似文献
7.
本文提出了一种震源孕育的数学物理模式,该模式把孕震过程分为扩容,包体形成与发展、流体扩散、失稳四个阶段。用数学物理方法研究了沿断裂带定向的圆柱形孕震区内的孕震过程。通过对这一过程的研究,得出了各孕震阶段持续时间的计算公式。计算结果与波速异常的实际观测结果符合较好。此外,还从理论上研究了确定两相介质中地震波传播速度的问题,给出了P、S波速度与速度比的计算公式,得出了一些定量结果。根据所述结果,对震前地震波速度异常的某些特征(异常持续时间、异常区形状大小及异常幅度)作出了一定的理论解释。最后,用量纲分析和相似理论方法对影响波速异常的一些因素作了简单的讨论。 相似文献
8.
利用1998年9月至2004年3月上旬中国地壳运动观测网络基准站GPS连续观测结果所获得的垂直位移时间序列,讨论了基准的选择,分析了基准站垂直位移的特点。取中国东部一组垂直位移变化形态基本一致、年速率较小的6个基准站作为垂直位移时间序列的基准。计算结果表明,每周的垂直位移解的精度可达3mm。与基准站的水平位移年速率相比,垂直位移年速率普遍较低;而与基准站的水平位移时间序列相比,一些基准站的垂直位移时间序列有非常显著的年周期变化,幅度达20～50mm。中国大陆西部基准站的年周期变化与地球自转有明显的相关性,并且符合地球自转守恒。基准站垂直位移的变化值得多方面深入研究 相似文献
9.
There are two kinds of methods in researching the crust deformation: geophysical method and geometrical (or observational)
method. Considerable differences usually exist between the two kinds of results, because of the datum differences, geophysical
model errors, observational model errors, and so on. Thus, it is reasonable to combine the two kinds of information to collect
the crust deformation information. To use the reliable geometrical and geophysical information, we have to control the observational
and geophysical model error influences on the estimated deformation parameters, and to balance their contributions to the
evaluated parameters. A hybrid estimation strategy is proposed here for evaluating the deformation parameters employing an
adaptively robust filtering. The effects of measurement outliers on the estimated parameters are controlled by robust equivalent
weights. Adaptive factors are introduced to balance the contribution of the geophysical model information and the geometrical
measurements to the model parameters. The datum for the local deformation analysis is mainly determined by the highly accurate
IGS station velocities. The hybrid estimation strategy is applied in an actual GPS monitoring network. It is shown that the
hybrid technique employs locally repeated geometrical displacements to reduce the displacement errors caused by the mis-modeling
of geophysical technique, and thus improves the precision of the estimated crust deformation parameters.
Supported by National Natural Science Foundation of China (Grant Nos. 40774001 and 40841021) and National High Technology
Research and Development Program of China (Grant No. 2007AA12Z331) 相似文献
10.
Characteristics of amplitude and duration for near fault strong ground motion from the 1999 Chi-Chi, Taiwan Earthquake 总被引：2，自引：0，他引：2
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. 相似文献
11.
Limited reports of repeat triangulation and levelling surveys carried out in the Koyna region by Survey of India, before and after the 1967 Koyna earthquake, are available. We analyse these observations of horizontal and vertical displacements to investigate whether analysis of these observations can provide additional constraints on the source parameters of the 1967 Koyna earthquake. We calculate surface displacements due to coseismic slip on the subsurface rupture of the 1967 Koyna earthquake and also due to the Koyna reservoir water load. We find that the reported displacements are too large to be attributed to the coseismic displacements and/or to the displacements induced by the reservoir water load. We conclude that these observations contain large random and systematic errors. 相似文献
12.
基于1976年唐山MS7.8地震的同震位移和现今GPS速度结果, 本文分析了该地震的同震破裂参数、 同震应变释放分布及其现今应变积累特征． 对唐山同震位移二维位错解析公式的拟合结果显示, 唐山地震前的断层闭锁深度约为18—23 km, 断层倾角可能介于74°—90°之间, 同震位错量约为3.1—3.4 m． 在同震过程中沿发震断层表现出显著的右旋错动特征, 在发震断层两侧沿NE向表现出左旋应变释放特征． 在本文现有的GPS测站密度和精度情况下, 尚无法识别出现今阶段沿唐山断裂的明显蠕滑特征． 唐山同震应变释放和现今GPS应变率积累结果均显示, 唐山断裂SE侧的剪切形变(速率)量值大于其NW侧, 同震与现今阶段的形变量值相差约1000倍． 相似文献
13.
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. 相似文献
14.
In this paper, we present a post-processing technique and an a posteriori error estimate for the Newmark method in structural dynamic analysis. By post-processing the Newmark solutions, we derive a simple formulation for linearly varied third-order derivatives. By comparing the Newmark solutions with the exact solutions expanded in the Taylor series, we achieve the local post-processed solutions which are of fifth-order accuracy for displacements and fourth-order accuracy for velocities in one step. Based on the post-processing technique, a posteriori local error estimates for displacements, velocities and, thus, also the total energy norm error estimate are obtained. If the Newmark solutions are corrected at each step, the post-processed solutions are of third-order accuracy in the global sense, i.e. one-order improvement for the original Newmark solutions is achieved. We also discuss a method for estimating the global time integration error. We find that, when the total energy norm is used, the sum of the local error estimates will give a reasonable estimate for the global error. We present numerical studies on a SDOF and a 2-DOF example in order to demonstrate the performance of the proposed technique. 相似文献
15.
本文详细地分析了强震加速度记录的数字化噪声。分析表明:数字化噪声由数字化设备的系统误差和操作者的随机读数误差迭加而成,随机数字化误差是具有各态历经性质的,其振幅按高斯规律分布的平稳随机过程,在其频谱组成中,长周期分量占明显的优势,因此将对二次积分加速度记录的位移曲线产生严重的影响。 研究表明:随机数字化噪声位移主要分布在周期大于25秒的频段,对加速度记录来说,分布在周期小于25秒的频段内,其随机噪声是相当小的(假定记录纸速为1厘米/秒)。因此,利用数字滤波技术,可以除去数字化加速度记录中的大部份随机数字化噪声。 作为实例,对一个典型的强震加速度记录进行了滤波,给出了低噪声的加速度记录和由此算出的位移曲线,且和未经滤波的相应记录及其位移进行了比较。 相似文献
16.
Rayleigh and Love wave group velocities in the Arctic islands and adjacent mainland of northern Canada exhibit large regional variations which can be attributed to variations in crustal structure. The shield and platform regions, the eastern Sverdrup basin, and the western Sverdrup basin are characterized by progressively slower velocities. Inversions of the regionalized group velocity data lead to three distinct shear-velocity models. The shield and platform model is similar to earlier models obtained for the Canadian shield. The Sverdrup basin models have low near-surface velocities which may correspond to thick accumulations of sediment. A sediment thickness of about 12 km obtained for the eastern basin corresponds to the maximum thickness inferred from earlier geological studies. An even thicker zone of low velocities occurs in the upper crust of the western basin. This zone may represent the true thickness of a very deep basin or slow velocities in basement rock may underlie the shallower sediments. A third alternative is that low apparent velocities for the western Sverdrup basin result from systematic errors in group velocity determinations produced by epicentral mislocations or origin time errors of the earthquakes used, but such mislocation or errors would have to be quite large to explain the observations. It is not possible to explain the group velocities across the basin areas by simply adding sediments to the shield and platform model. The resulting discrepancies with the data suggest an altogether different crustal structure beneath the basin than that beneath the shield and platform areas. 相似文献
17.
Structures undergoing inelastic displacements during earthquake ground motions are known to sustain some amount of residual displacements, which may make those 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 ductility ratio. Such oscillators belong to the class of bilinear hysteresis models applicable to steel structures, with post-yield-stiffness ratio taken as zero, and may be used for the conservative estimates of residual displacements when the post-yield-stiffness ratio is unlikely to become negative. Statistical estimation of residual displacement spectrum via normalization with respect to inelastic or elastic spectral displacements is considered and expressions are proposed for both types of normalizations. The statistical dependence of residual displacement on the seismological and site parameters and strong motion duration is also studied and a simple scaling model is proposed in terms of earthquake magnitude, epicentral distance, and geologic site condition parameter for the seismic region of western U.S.A. According to this model, the variation of residual displacement with period primarily depends on the site conditions, and the residual displacements are more sensitive to ductility ratio at low ductility ratios. 相似文献
18.
Wide-angle reflections are now routinely recorded in high resolution explosion seismics to study the crustal structure. Use of Dix's hyperbolic approximation to the nonhyperbolic wide-angle reflection travel times causes major errors in the determination of interval velocities and layer thicknesses of a stack of horizontal velocity layers. Here we propose a layer stripping method to directly calculate the interval velocities and layer thicknesses in a vertically heterogeneous earth from the strong and reliable wide-angle reflected events. Synthetic reflection travel times, at wide-angle range, for a given velocity model, contaminated by some random errors, have been used to demonstrate the reliability of the algorithms to determine the interval velocities and thicknesses of various layers. The method has also been tested on two field examples along two deep seismic sounding (DSS) profiles with well identified wide-angle reflection travel times, which illustrates the practical feasibility of the proposed method. 相似文献
19.
While rockbursts from underground copper mining in Western Poland normally produce surface peak ground accelerations (PGA) and velocities of 0.05–0.1 g and 1–3 cm/s, occasionally these peak motions may exceed 0.15 g and 10 cm/s, respectively. These larger motions are of considerable concern and an investigation has been undertaken to define the nature of these larger induced ground motions. This paper compares these rockburst motions with low intensity earthquakes. Various strong motion parameters such as PGA, peak ground velocity (PGV) and displacements as well as strong motion duration, Arias intensity, Fourier and response spectra are compared with those from earthquakes. It is concluded that although short duration is the most obvious parameter that differentiates rockbursts from earthquakes, in fact their high dominant frequencies, which result in high PGA/PGV ratios differentiate them the most. Two types of rockburst-induced ground motions are indicated in this paper: typical—with 3–6 months return period and characteristic, high frequency content—as well as rare events similar to shallow, low intensity earthquakes. 相似文献
20.
本文根据北京电信传输地震台网在1978-1984年期间的395次地震[1.0ML6.2;10△600km]资料,讨论了近震震级 ML 的量规函数、台基校正、仪器分量校正和震源区校正等,并着重研究了信号持续时间震级 MD 的不同测定方法和误差.结果表明,如果采用本文中所述的方法,不需添加任何校正值,只用少数几个台甚至仅用一个台的资料就可逼近无偏震级.必须指出,持续时间震级 MD 在震级大于4.8时可产生震级饱和现象,对此,用另一条具有较大斜率的方程拟合便可得到满意的结果. 相似文献