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1.
Chi Hsin Lin Vincent W. Lee Maria I. Todorovska Mihailo D. Trifunac 《Soil Dynamics and Earthquake Engineering》2010
The zero-stress boundary conditions at the surface of the half-space in the presence of surface and sub-surface cavities for in-plane, incident cylindrical P- and SV-waves have always posed challenging problems. The outgoing cylindrical P- and SV-waves can be represented by Hankel functions of radial distance coupled with the sine and cosine functions of angle. Together, at the half-space surface the P- and SV-wave functions are not orthogonal over the semi-infinite radial distance from 0 to infinity. Thus, to simultaneously satisfy the zero in-plane, normal, and shear stresses, an approximation of the geometry is often made. This paper presents an analytical formulation of the boundary-valued problem, where the Hankel wave functions are expressed in integral form, changing the representation from cylindrical to rectangular coordinates, so that the zero-stress boundary conditions at the half-space surface can be applied in a more straightforward way. 相似文献
2.
Wave Generation from Explosions in Rock Cavities 总被引：1，自引：0，他引：1
—?We have developed a measurement method to monitor P- and S-waves generated from laboratory-scale explosions in meter-sized rock samples at a series of stations, as well as invented a device to drill spherical cavities in rock, with diameters up to 10?centimeters. We applied these to experiments in Bedford limestone in which spherical/cylindrical explosives (0.2 to 1.9?g) were centrally placed in 1.2- to 3-cm diameter cavities. Stress waves generated by the explosions were recorded within a radius of 25?cm. The radial stress wave records and post-explosion studies demonstrate that S-waves are generated from explosions in cavities as a result of both wave mode-conversion from the cavity wall and crack propagation in rocks. The experimental results of wave generation from the explosions in spherical and cylindrical cavities demonstrate the cavity geometrical effect on the resulting wave pattern. The P- and S-waves generated by explosions and crack propagation in rocks are analyzed. A simple analytic model for P-wave generation is proposed to explain the differences of P-wave-induced displacement histories between the observed waveforms and those predicted by a step-pressure source. Generally, the qualitative predictions of this model fit the observations. The present results demonstrate the importance of rock cracking and cavities in P- and S-wave generation. 相似文献
3.
采用刚度矩阵方法结合Hankel积分变换,求解了层状黏弹性半空间中球面SH、P和SV波的自由波场.首先,在柱坐标系下建立层状黏弹性半空间的反轴对称(柱面SH波)和轴对称(柱面P-SV波)情况精确动力刚度矩阵.进而由Hankel变换将空间域内的球面波展开为波数域内柱面波的叠加,然后将球面波源所在层的上下端面固定,求得固定层内的动力响应和固定端面反力,将固端反力反向施加到层状黏弹性半空间上,采用直接刚度法求得固端反力的动力响应,叠加固定层内和固端反力动力响应,求得波数域内球面波源动力响应.最后由Hankel积分逆变换求得频率-空间域内球面波源自由场,时域结果由傅里叶逆变换求得.文中验证了方法的正确性,并以均匀半空间和基岩上单一土层中球面SH、P和SV波为例分别在频域和时域内进行了数值计算分析.研究表明基岩上单一土层中球面波自由场与均匀半空间情况有着本质差异;基岩上单一土层中球面波位移频谱峰值频率与场地固有频率相对应,基岩面的存在使得基岩上单一土层地表点的位移时程非常复杂,振动持续时间明显增长;阻尼的增大显著降低了动力响应的峰值,同时也显著减少了波在土层的往复次数. 相似文献
4.
Summary Theoretical expressions are derived for the displacement, velocity and stress in the time domain induced by an axially symmetric shearing stress applied at the inner surface of a spherical cavity in a hornogeneous, isotropic, elastic medium of infinite extent. Theoretical seismograms are computed for a step source and for three sources with exponential decay in time. A satisfactory time-dependence of the source can be obtained by combining the step source with one or more exponentially decaying sources. 相似文献
5.
The compression of soil grain and pore fluid as well as viscid coupling of pore fluid and soil skeleton is considered, the scattering problem of incident plane P1 wave （fast compressional wave） by an infinite cylindrical shell deeply embedded in isotropic saturated soils is studied by adopting the amended Biot model, amplitude equations about potential functions of scattering and refracting fields are obtained, and the effect of dimensionless frequencies and shell thickness on the back-scattering spectra and dynamic stress concentration factors of two types of cylindrical shells with high and low rigidity are numerically computed and analyzed. 相似文献
6.
Summary The transmission of elastic pulses through solid bars has been investigated experimentally with particular reference to the shape of the bars. A single input pulse giving rise to a series of pulses at the receiver which help in the computation of dilatational and rotational velocities in the material has been exploited for the experimental work, and it has been found that the method is applicable to cylindrical and cubical (square) bars in an equal manner. Results of the experimental investigations carried out in cylindrical and square bars of brass are compared and found to be in good agreement. Also results in square bars of Aluminium, Steel, and a few rock samples are reported. The rock samples studied include limestone, sandstone and a crypto-crystalline rock. An attempt to study the applicability of this method to rectangular bars has also been made and the results obtained are consistent and in agreement with the results due to cylindrical and square bars.N.G.R.I.-68-117. 相似文献
7.
Co-seismic Coulomb stress changes on the northern Tanlu fault zone caused by the Tohoku-Oki MW9.0 earthquake* 
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下载免费PDF全文 Based on the spherical earth dislocation theory and a fault slip model of the Tohoku-Oki MW9.0 earthquake, the co-seismic Coulomb failure stress changes (ΔCFS) on the northern Tanlu fault zone at depths of 0–40 km are calculated. By comparing two sets of results from the spherical earth dislocation theory and the semi-infinite space one, the effect of earth curvature on the calculation results is analyzed quantitatively. First, we systematically summarize previous researches related to the northern Tanlu fault zone, divide the fault zone as detailed as possible, give the geometric parameters of each segment, and establish a segmented structural model of the northern Tanlu fault zone. Second, we calculate the Coulomb stress changes on the northern Tanlu fault zone by using the spherical earth dislocation theory. The result shows the Coulomb stress changes are no more than 0.003 MPa, which proves the great earthquake did not significantly change the stress state of the fault zone. Finally, we quantitatively analyze the disparities between the results of semi-infinite space dislocation theory and the spherical earth one. The average disparity between them is about 7.7% on the northern Tanlu fault zone and is 16.8% on the Fangzheng graben, the maximum disparity on this graben reaches up to 25.5%. It indicates that the effect of earth curvature can not be ignored. So it’s necessary to use the spherical earth dislocation theory instead of the semi-infinite space one to study the Coulomb stress change in the far field. 相似文献
8.
More than a thousand acoustic-emission (AE) hypocenters were determined in a cylindrical andesite specimen under two-stage uniaxial creep at stresses of 204 and 214 MPa. Strains were monitored for 6 peripheral points at the middle part of the cylindrical specimen's wall. The strain data indicate gradual increase of nonuniform deformation during steady creep and strong intensification of the nonuniformity during acceleration creep and, therefore, biased stress distribution within the specimen. The correlation between dilatant strain and AE hypocenters was investigated for whether or not tensile cracks emit AE. The region with high AE activity shows only a small dilatant strain. This negative correlation between AE and the dilatant region may eliminate tensile cracks as possible AE sources. A composite focal-mechanism solution of local AE events, covering a wide solid angle of the focal hemisphere, indicates that shear fractures emit AE waves. The direction of the compressional axis in this solution shows a significant deviation from that inferred from the applied external force, suggesting that the local stress field is governed by preexisting weak zones that are, presumably, produced by tensile cracks within the specimen. AE hypocenters tended to form clusters during steady creep under the constant compressional stress. During acceleration creep caused by a small step increase of the external stress, the preceding clusters disappeared while a new cluster appeared in an incipient fault plane. This suggests that changes in seismicity pattern such as migrations or quiescences of swarm—important clues for earthquake predictions—may be caused by an instantaneous change in the tectonic-stress levels. 相似文献
9.
Abstract The solution of the full nonlinear hydromagnetic dynamo problem is a major numerical undertaking. While efforts continue, supplementary studies into various aspects of the dynamo process can greatly improve our understanding of the mechanisms involved. In the present study, the linear stability of an electrically conducting fluid in a rigid, electrically insulating spherical container in the presence of a toroidal magnetic field Bo(r,θ)lø and toroidal velocity field Uo(r,θ)lø, [where (r,θ,ø) are polar coordinates] is investigated. The system, a model for the Earth's fluid core, is rapidly rotating, the magnetostrophic approximation is used and thermal effects are excluded. Earlier studies have adopted a cylindrical geometry in order to simplify the numerical analysis. Although the cylindrical geometry retains the fundamental physics, a spherical geometry is a more appropriate model for the Earth. Here, we use the results which have been found for cylindrical systems as guidelines for the more realistic spherical case. This is achieved by restricting attention to basic states depending only on the distance from the rotation axis and by concentrating on the field gradient instability. We then find that our calculations for the sphere are in very good qualitative agreement both with a local analysis and with the predictions from the results of the cylindrical geometry. We have thus established the existence of field gradient modes in a realistic (spherical) model and found a sound basis for the study of various other, more complicated, classes of magnetically driven instabilities which will be comprehensively investigated in future work. 相似文献
10.
本文采用三维应力-速度有限差分(SV-FD)方法,数值模拟了横向各向同性(TI)地层对称主轴与井轴斜交情况下正交偶极子声源激发的井孔声场.主要解决了与倾斜角有关的三维空间弹性模量矩阵的推导,柱坐标系下应力-速度有限差分方程组的建立,井轴上场点奇异性与内边界处理等几个关键问题,提高了计算精度.在横向各向同性地层对称主轴与井轴平行的情况下,与实轴积分法所得结果进行了对比,验证了本文方法的正确性.计算了不同倾角情况下xx和yy两分量的弯曲波,并用频域加权相似法提取了弯曲波频散曲线,结果显示了横向各向同性介质中不同方向偏振的弯曲波传播的分裂现象,其频散曲线在低频段分裂,随频率增大而逐渐重合.弯曲波低频截止频率处速度与理论公式得到的横波速度基本符合. 相似文献
11.
利用辽宁省地震局沈阳数字地震台网1999年6月至2000年5月的波形资料,采用两种不同的几何扩散模型,计算了岫岩地震序列的单台和多台平均视应力、差视应力值。分析了1999年岫岩Ms5.4地震序列单台和多台视应力的时间演化特征,比较了两种不同几何模型视应力和差视应力随时间的变化特征以及同一地震的视应力。结果表明:①对于同一地震而言,几何扩散模型得到的视应力值比分三段几何扩散模型的大,考虑能量补偿得到的视应力要比未考虑能量补偿的要大。②该序列视应力的变化特征主要表现为:主震前一段时间视应力水平较低,主震前几天地震视应力水平升高,主震与最大余震期间,视应力处于一个较高的水平,最大余震发生后,视应力逐渐降低,并恢复到震前水平。这表明视应力为预测震后趋势提供了一个有用的依据;③无论是采用球面几何扩散模型还是分三段几何扩散模型,无论是单台视应力结果还是多台平均视应力结果,无论考虑能量补偿与否,在震后趋势的判定上几乎没有差异;④无论是采用球面几何扩散模型还是采用分三段几何扩散模型,差视应力在Ms5.4主震和Ms5.1余震发生前短时间内都具有快速的升高变化过程。 相似文献
12.
本文对球面波反射P波反射系数计算公式进行了推导,根据推导公式计算出第I类AVO和第Ⅲ类AVO介质中反射系数及相位随入射角的变化,并与基于平面波的Zoeppritz方程计算的结果进行对比.结果显示,对于第I类AVO介质,球面波反射系数在临界角附近较基于平面波的Zoeppritz方程计算结果更精确;同时受界面深度的影响较大,随深度的增加,球面波AVO趋势接近平面波AVO.最后,通过数值模拟技术,对模型数据和实际数据进行模拟,对平面波AVO道集和球面波AVO道集进行了验证分析.浅层的第I类AVO现象,在近临界角和超临界角处折射引起反射系数与相位的变化较大,对于第Ⅲ类AVO现象,由于不存在临界角问题,球面波模拟结果与基于平面波的Zoeppritz计算结果差别较小.上述计算分析,可为实际资料的大偏移距道集的AVO分析提供理论基础. 相似文献
13.
In this paper, we derive an approximation of the SS-wave reflection coefficient and the expression of S-wave ray elastic impedance (SREI) in terms of the ray parameter. The SREI can be expressed by the S-wave incidence angle or P-wave reflection angle, referred to as SREIS and SREIP, respectively. Our study using elastic models derived from real log measurements shows that SREIP has better capability for lithology and fluid discrimination than SREIS and conventional S-wave elastic impedance (SEI). We evaluate the SREIP feasibility using 25 groups of samples from Castagna and Smith (1994). Each sample group is constructed by using shale, brine-sand, and gas-sand. Theoretical evaluation also indicates that SREIP at large incident angles is more sensitive to fluid than conventional fluid indicators. Real seismic data application also shows that SREIP at large angles calculated using P-wave and S-wave impedance can efficiently characterize tight gas-sand. 相似文献
14.
A local time-domain transmitting boundary for simulating cylindrical elastic wave propagation in infinite media 总被引：3，自引：0，他引：3
Finite element simulation of the time-dependent wave propagation in infinite media requires enforcing the transmitting boundary to replace the truncated far-field infinite domain so as to model the effect of the wave radiation towards infinity. This paper proposed a novel local time-domain transmitting boundary for simulating the cylindrical elastic wave radiation problem. This boundary is a mechanical model consisting of the spring, dashpot and mass elements, with the auxiliary degrees of freedom introduced, which is dynamically stable and easily implemented into the commercial finite element codes. Numerical analysis of the cylindrical elastic wave radiation problem indicates that the proposed transmitting boundaries with the order N=3 for cylindrical P and SV waves and with the order N=4 for cylindrical SH wave have very high accuracy, even when the artificial boundary at wave source. The proposed transmitting boundary with order N=0 can be applied approximately to the general two-dimensional infinite elastic wave problems that contain the more complex outgoing wave fields at artificial boundary than the cylindrical waves. The plane-strain Lamb problem is analyzed with the acceptable engineering accuracy achieved. On the other hand, the proposed transmitting boundary with higher order can be a tool to localize the temporal convolution that appears in an exact time-domain transmitting boundary for the general infinite wave problems. This potential applicability is mentioned. 相似文献
15.
基于黏弹性人工边界的地震动斜入射方法模拟平面SV波不同角度入射情况,分别采用声固耦合法和附加质量法模拟闸室内水体,研究超高水头船闸闸室位移、应力和塑性损伤等地震反应,对比两种水体模拟方法计算结果的异同。结果表明:(1)整体上,两种方法计算得出的左、右闸墙地震反应结果随入射角度变化的规律基本一致;左闸墙受拉损伤的最大值均出现在入射角15°时,右闸墙受拉损伤的最大值均出现在入射角35°时;地震波入射角度对超高水头船闸动力响应影响较大,设计时应考虑地震波斜入射的影响。(2)当入射角较大时,采用声固耦合法计算的闸墙相对位移极值、主应力极值和受拉损伤结果偏保守的概率更大,对超高水头船闸结构设计来说更为安全。(3)建议两种计算方法相互参考和校核,推荐采用偏安全的结果进行超高水头船闸结构设计。 相似文献
16.
自然界的裂隙排列并非都是直立的,在复杂地壳应力作用下裂隙排列很可能是倾斜的.本文从各向异性弹性动力学基本方程出发,在特征矩阵方法基础上提出了计算任意倾斜裂隙介质水平界面上的反射、透射系数的简单方法,并利用该方法计算了倾斜裂隙介质P-P波、P-SV波和P-SH波的反透射系数.结果表明,P-P波、P-SV波和P-SH波的反透射系数与倾斜裂隙的倾角、测线方位以及偏移距这些物理参数之间存在一定的依赖关系.此外我们计算了C波的零入射相角时的反射系数,发现该反射系数跟裂隙倾角、裂隙的方位角有着明显的对应规律,且各向异性越强时,该反射系数越大.这些研究对于深入了解倾斜裂隙的动力学特征具有一定的意义. 相似文献
17.
浅埋圆柱形弹性夹杂附近等腰三角形凸起地形引起的SH波的散射 总被引：4，自引：0，他引：4
文章利用“契合”思想,给出了地下弹性夹杂与地面上的等腰三角形凸起地形引起的SH波散射问题的解析解答。利用复平面下坐标移动,通过区域Ⅰ和区域Ⅱ以及区域Ⅱ和区域Ⅲ的“公共边界”位移应力连续条件,建立起求解该问题的无穷代数方程组并截断有限项进行求解,最后通过具体算例及结果分析得出相应结论。 相似文献
18.
19.
Prof. S. K. Chakraborty 《Pure and Applied Geophysics》1956,35(1):25-32
Summary Disturbances generated by pressure on the surface of a spherical cavity inside (i) a dispersive medium, (ii) a medium having transverse isotropy about the radius vector have been considered. Finally, a brief discussion of the propagation of waves in visco-elastic media has been added.I wish to express my gratefulness to Professor B. B.Sen, for his kind help in the preparation of the paper. 相似文献
20.
2002年在京津冀地区进行了45个测点的地磁三分量测量,对测量资料进行通化处理,通化时间为2002年5月5日16～18时（世界时）. 通化后的观测均方差分别优于1.5nT（地磁场总强度F）,0.5′(磁偏角D和磁倾角I). 将国际参考地磁场（IGRF2000）作为地磁正常场,建立了京津冀地区地磁异常场的球冠谐模型（BTHASCH）. 球冠极的空间位置坐标为39.5°N和117.0°E,球冠半角为4°. 在模型计算过程中,球冠谐函数的截断阶数分别取为1～10. 经综合比较, 最终采用的截断阶数为5. 建立了京津冀地区参考地磁场的球冠谐模型（BTHGRF）.根据模型,绘制了京津冀地区地磁异常场图(ΔX、ΔY、ΔZ、ΔF、ΔD、ΔI)和京津冀地区地磁图(X、Y、Z、F、D、I). 相似文献