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1.
R.-G. FERBER 《Geophysical Prospecting》1988,36(8):857-877
A new time-domain method is introduced for the calculation of theoretical seismograms which include frequency dependent effects like absorption. To incorporate these effects the reflection and transmission coefficients become convolutionary operators. The method is based on the communication theory approach and is applicable to non-normal incidence plane waves in flat layered elastic media. Wave propagation is simulated by tracking the wave amplitudes through a storage vector inside the computer memory representing a Goupillaud earth model discretized by equal vertical transit times. Arbitrary numbers of sources and receivers can be placed at arbitrary depth positions, while the computational effort is independent of that number. Therefore, the computation of a whole plane-wave vertical seismic profile is possible with no extra effort compared to the computation of the surface seismogram. The new method can be used as an aid to the interpretation of plane-wave decomposed reflection data where the whole synthetic vertical seismic profile readily gives the interpreter the correct depth position of reflection events. 相似文献
2.
目前在地震勘探频带范围内通常假设品质因子Q与频率无关,且呈衰减各向同性.事实上,相比较速度各向异性,介质的衰减各向异性同样不可忽视.本文将衰减各向异性和速度各向异性二者与常Q模型相结合,建立了黏弹性衰减VTI介质模型,并基于分数阶时间导数理论,给出了对应的本构关系和波动方程.利用均匀平面波分析和Poynting定理,推导出准压缩波qP、准剪切波qSV和纯剪切波SH的复速度、相速度、能量速度以及品质因子的解析表达式.对模型的正确性进行了数值验证,并分析了qP,qSV和SH波在介质中的传播特性.数值试验结果表明:本模型能够实现理想的恒定Q行为,表现了品质因子和速度的各向异性特征,显示出黏弹性增强将导致能量速度和相速度的频散曲线变化剧烈;速度和衰减各向异性参数与传播角度之间的耦合效应对qP,qSV和SH波的速度和能量影响明显;qP,qSV和SH波的频散曲线和波前面随着衰减各向异性强度的改变发生显著变化,其中耦合在一起的qP和qSV波变化趋势相同,而SH波与它们呈现相反的变化规律.本研究为从常Q模型角度分析地震波在衰减各向异性黏弹性介质中的传播特征奠定了理论基础. 相似文献
3.
为了分析台风这类强对流诱发平流层重力波的过程,本文利用中尺度数值模式WRF-ARW(V3.5)和卫星高光谱红外大气探测器AIRS数据对2011年第9号强热带气旋"梅花"的重力波特征进行了分析.首先,针对模式输出的垂直速度场资料的分析表明,台风在对流层各个方向上几乎都具有诱发重力波的能量,而在平流层内则呈现出只集中于台风中心以东的半圆弧状波动,且重力波到达平流层后其影响的水平范围可达1000km.此外,平流层波动与对流层雨带在形态、位置以及尺度上均具有一定的相似性.其次,对风场的分析结果表明,不同高度上波动形态的差异主要是由于重力波垂直上传的过程中受到了平流层向西传的背景风场以及风切变的调制作用,揭示了重力波逆着背景流垂直上传的特征.随后,基于FFT波谱分析的结果表明,"梅花"诱发的平流层重力波水平波长中心值达到了1000km,周期在15~25h,垂直波长主要在8~12km.最后,利用AIRS观测资料分析了平流层30~40km高度上的大气波动,得到了与数值模拟结果相一致的半圆弧状波动.对比结果也验证了WRF对台风诱发平流层重力波的波动形态、传播方向、不同时刻扰动强度的变化以及影响范围的模拟效果.此外,也揭示了多资料的结合对比有助于更加全面地了解台风诱发平流层重力波的波动特征. 相似文献
4.
本文以Biot提出的流体饱和多孔介质波动理论为基础, 建立了成层地基模型, 把地下水位以下的饱和土层用水饱和多孔介质模拟, 地下水位以上土层用气饱和多孔介质模拟. 通过研究入射平面简谐波在成层地基中的传播, 分析了地下水位变化对地震地面运动的影响. 结果表明: P波入射下, 当土体骨架相对刚度较小时, 地下水位变化对地表位移尤其是竖向地表位移幅值影响较大, 随着地下水位的下降, 竖向位移逐渐增加, 相对应的峰值频率逐渐减小; 当土体骨架相对刚度较大时, 地下水位变化对地面运动影响不大. 相似文献
5.
Hua‐You Chai Tian‐Bin Li Kok‐Kwang Phoon Elton J. Chen Dian‐Ji Zhang 《Geophysical Prospecting》2017,65(4):992-1003
In the free state, Rayleigh waves are assumed to travel in the form of planar wavefronts. Under such an assumption, the propagation behaviour of the modes of Rayleigh waves in layered half‐spaces is only frequency dependent. The frequency behaviour, which is often termed as dispersion, is determined by the shear wave velocity profile of layered soils within the depth related to wavelength (or frequency). According to this characteristic, the shear wave velocity profile can be back‐analysed from the dispersion. The technique is widely used in the surface wave testing. However, the wavefronts of Rayleigh waves activated by the surface sources are non‐planar. The geometric discrepancy could result in Rayleigh waves manifesting distance‐dependent behaviour, which is referred to as spatial behaviour in this paper. Conventional analysis ignoring this spatial behaviour could introduce unexpected errors. In order to take the effects of sources on the propagation behaviour into account, a new mathematical model is established for Rayleigh waves in layered elastic media under vertical disc‐like surface sources using the thin‐layer method. The spatial behaviour of the activated modes and the apparent phase velocity, which is the propagation velocity of Rayleigh waves superposed by the multiple modes, are then analysed. Aspects of the spatial behaviour investigated in this paper include the equilibrium path, the particle orbit, and the geometric attenuation of the activated Rayleigh waves. The results presented in this paper can provide some guidelines for developing new inverse mathematical models and algorithms. 相似文献
6.
Inertia-gravity waves in the troposphere and lower stratosphere associated with a jet stream exit region 总被引：1，自引：0，他引：1
Radar measurements at Aberystwyth (52.4°N, 4.1°W) of winds at tropospheric and lower stratospheric heights are shown for 12–13 March 1994 in a region of highly curved flow, downstream of the jet maximum. The perturbations of horizontal velocity have comparable amplitudes in the troposphere and lower stratosphere with downward and upward phase propagation, respectively, in these two height regions. The sense of rotation with increasing height in hodographs of horizontal perturbation velocity derived for hourly intervals show downwards propagation of energy in the troposphere and upward propagation in the lower stratosphere with vertical wavelengths of 1.7 to 2.3 km. The results indicate inertia-gravity waves propagating in a direction similar to that of the jet stream but at smaller velocities. Some of the features observed contrast with those of previous observations of inertia-gravity waves propagating transverse to the jet stream. The interpretation of the hodographs to derive wave parameters has taken account of the vertical shear of the background wind transverse to the direction of wave propagation. 相似文献
7.
Wave-induced steady streaming,mass transport and net sediment transport in rough turbulent ocean bottom boundary layers 总被引：1，自引：0，他引：1
The interaction between two important mechanisms which causes streaming has been investigated by numerical simulations of the seabed boundary layer beneath both sinusoidal waves and Stokes second order waves, as well as horizontally uniform bottom boundary layers with asymmetric forcing. These two mechanisms are streaming caused by turbulence asymmetry in successive wave half-cycles (beneath asymmetric forcing), and streaming caused by the presence of a vertical wave velocity within the seabed boundary layer as earlier explained by Longuet-Higgins. The effect of wave asymmetry, wave length to water depth ratio, and bottom roughness have been investigated for realistic physical situations. The streaming induced sediment dynamics near the ocean bottom has been investigated; both the resulting suspended load and bedload are presented. Finally, the mass transport (wave-averaged Lagrangian velocity) has been studied for a range of wave conditions. The streaming velocities beneath sinusoidal waves (Longuet-Higgins streaming) is always in the direction of wave propagation, while the streaming velocities in horizontally uniform boundary layers with asymmetric forcing are always negative. Thus the effect of asymmetry in second order Stokes waves is either to reduce the streaming velocity in the direction of wave propagation, or, for long waves relative to the water depth, to induce a streaming velocity against the direction of wave propagation. It appears that the Longuet-Higgins streaming decreases as the wave length increases for a given water depth, and the effect of wave asymmetry can dominate, leading to a steady streaming against the wave propagation. Furthermore, the asymmetry of second order Stokes waves reduces the mass transport (wave-averaged Lagrangian velocity) as compared with sinusoidal waves. The boundary layer streaming leads to a wave-averaged transport of suspended sediments and bedload in the direction of wave propagation. 相似文献
8.
An experiment was carried out to develop a technique to measure shear wave velocity simultaneously with the standard penetration test popular in soil engineering. In the standard penetration test an impact at the bottom of a borehole is produced by weight dropping and may be expected to generate seismic waves. A three-component geophone was set on the ground surface near the borehole and the waves generated were recorded with a magnetic recorder at successive depths of the penetration test. The predominance of the SV wave obtained with this simple method was assured by measurement of the particle orbit. Signal amplitudes decrease with depth and become less than the noise level at a certain depth. Therefore records from deeper sources must be processed to disclose the shear waves. Since waveforms of SV events generated by blows of the penetration test at a given depth are very similar, the signal to noise ratio would be expected to be improved by a stack of wave trains. A paste-up of the radial component after stacking was compared with that before stacking and a refinement was clearly recognized. A vertical distribution of shear wave velocity was obtained by reading the onset time at each depth. Shear wave velocities thus obtained were compared with N values from the standard penetration test and specific resistivities from electrical logging in the same borehole. The data were mutually consistent. This experiment showed that a convenient, precise shear wave velocity measurement can be conducted during the routine work of a standard penetration test. 相似文献
9.
BRUCE J. VERWEST 《Geophysical Prospecting》1989,37(2):149-166
The study of wave propagation in media with elliptical velocity anisotropy shows that seismic energy is focused according to the horizontal component of the velocity field while the vertical component controls the time-to-depth relation. This implies that the vertical component cannot be determined from surface seismic velocity analysis but must be obtained using borehole or regional geological information. Both components of the velocity field are required to produce a correctly focused depth image. A paraxial wave equation is developed for elliptical anisotropic wave propagation which can be used for modelling or migration. This equation is then transformed by a change of variable to a second paraxial equation which only depends on one effective velocity field. A complete anisotropic depth migration using this transformed equation involves an imaging step followed by a depth stretching operation. This allows an approximate separation or splitting of the focusing and depth conversion steps of depth migration allowing a different velocity model to be used for each step. This split anisotropic depth migration produces a more accurate result than that obtained by a time migration using the horizontal velocity field followed by an image-ray depth conversion using the vertical velocity field. The results are also more accurate than isotropic depth migration and yield accurate imaging in depth as long as the lateral variations in the anisotropy are slow. 相似文献
10.
Bagus Jaya Santosa 《中国地震研究》2008,22(2):206-217
The S wave velocity structure of the earth below Eastern Southeast Asia has been investigated by analyzing the seismogram from surface wave to multiple depth waves in the time domain and three Cartesian components simultaneously. The wave passes across the front area of subduction zone between the Philippine plate and the Asian plate. The main data are waveform comparisons, instead of the arrival times. The synthetic seismogram is calculated using the GEMINI method. The synthetic seismogram constructed by PREMAN global earth model deviates greatly from the measured one. To solve this problem, corrections are needed for the β speed structure. Corrections cover the gradient change of βh, which turns from negative to positive in upper mantle layers as in the PREMAN, change of earth crust depth and change of zero order coefficients of β velocity function in all earth mantle layers. So, the fitting is obtained, as well as the arrival time or the waveform of Love and Rayleigh surface waves, the S wave and the repetitive depth waves ScS2 and ScS3. This result reveals that the Southeast Asia, being stretched due to tectonic release, has a mantle in some parts with negative anomaly of S wave velocity and vertical anisotropy in all earth mantle layers. 相似文献
11.
The surface motion during an earthquake is different from point to point depending on the propagation properties of the seismic waves. Rocking and torsion are thus present in the free field, in proportion to the spatial derivatives of the surface motion with respect to a given direction. These derivatives are inversely proportional to the apparent wave velocity in that direction, so the smaller the wave apparent velocity, the more important its contribution to the rotations. In this respect, a marked contribution to surface rotations from surface waves is expected. A mathematical model is presented, based on a detailed representation of soil impedance, an approximate identification of surface waves and a deconvolution of body waves in P and SV contributions. Through this model the surface motion obtained from the records of strong-motion accelerometers can be expressed as a superposition of plane waves of known wavelengths. Rocking response spectra are computed and results are compared with previously published spectra. A sensitivity analysis is performed on some parameters of the model. 相似文献
12.
The present paper investigates the effect of voids on the propagation of surface waves in a homogeneous micropolar elastic
solid medium which contains a distribution of vacuous pores (voids). The general theory for surface wave propagation in micropolar
elastic media containing voids has been presented. Particular cases of surface waves (Rayleigh’s, Love’s and Stoneley’s) in
micropolar media which contain vacuous pores have been deduced from the above general theory. Discussions have been made in
each case to highlight the effect of voids and micropolar character of the material medium separately. Their joint effect
has also been studied in details. Modulation of Rayleigh wave velocity has been studied numerically. It is observed that Love
waves are not affected by the presence of voids. 相似文献
13.
地下岩石结构/构造和矿物组成在小尺度上存在的不均匀性和各向异性会导致地震波速度的分形分布，进而衍生出自组织介质模型. 本文针对地球内部岩浆垂向侵入及横向溢流为特征的岩浆作用，开展自相似型各向异性自组织介质的地震波动力学响应研究. 基于二维自组织介质模型和声波方程，本文利用有限差分法模拟了不同强度岩浆侵入和溢流作用形成的自组织介质中地震波场，并进行了波场特征分析. 研究结果表明：（1）在横向溢流作用为主的自组织介质中，横向相关长度小于地震波波长的条件下，聚焦效应随着横向相关长度的增大而增强，地震波能量随之增强；反之，在横向相关长度大于地震波波长的条件下，散射效应随横向相关长度的增大而增强，地震波能量随之减弱. （2）在垂向侵入作用为主的自组织介质中，随着垂向相关长度增大，散射效应增强，地震波的能量也随之迅速减弱. （3）岩浆作用的自组织强度增强，地震波的能量增大，而中心频率无变化. （4）自组织介质具有相同的小尺度扰动，其速度梯度背景越小，地震波能量在炮点附近越集中. （5）当多层自组织介质共存，特征层位的波场特征仍以各自的自组织特性为主，因此利用实际资料中不同层位的地震反射特征可推测地下介质的自组织性质. 相似文献
14.
相速度和群速度是研究地震波传播规律和描述介质特性的重要参数,是弹性波传播理论中的核心内容,在理论研究和实际应用中有重要作用.本文根据VTI介质的刚度矩阵,利用Bond变换建立了TTI介质刚度矩阵.再利用TTI介质刚度矩阵,结合弹性动力学的本构方程、牛顿运动微分方程和几何方程,得到了三维TTI介质弹性波波动方程和Christoffel方程.通过本征值方法求解Christoffel方程,推导了三维TTI介质弹性波相速度的解析表达式.利用Berryman和Crampin推导各向异性介质群速度公式,根据三维TTI介质的相速度解析式推导了三维TTI介质群速度解析表达式.数值试例表明,随着各向异性介质参数改变,TI介质弹性波相速度变化较为平缓,群速度变化较为剧烈,qP波和SH波速度变化较为平缓,qSV波速度变化较为剧烈. 相似文献
15.
地震波在各向异性介质中以一个准P波(qP)和两个准S波(qS1和qS2)的形式传播.研究三种波的相速度、群速度以及偏振方向等传播性质能够为各向异性介质中的正反演问题提供有效支撑.具有比横向各向同性(TI)介质更一般对称性的正交各向异性介质通常需要9个独立参数对其进行描述,这使得对传播特征的计算更为复杂.当两个准S波速度相近时具有耦合性,从而令慢度的计算产生奇异性.因此,奇异点(慢度面的鞍点和交叉点)附近的反射与透射(R/T)系数的求解不稳定,会导致波场振幅不准确.本文首次通过结合耦合S波射线理论和基于迭代的各向异性相速度与偏振矢量的高阶近似解,得到了适用于正交各向异性介质以qP波入射所产生的二阶R/T系数的计算方法.与基于一阶近似的结果相比,基于二阶近似的方法提高了qP波R/T系数的精度,能得到一阶耦合近似无法表达的准确的qP-qS转换波的R/T系数解,且方法适用于较强的各向异性介质. 相似文献
16.
Summary Two different viewpoints of the phase velocities of the elastic surface waves in isotropic, laterally inhomogeneous media have led to inconsistent results. Arguments in terms of surface wave modes give the conclusion that the phase velocity is independent of the propagation direction, while the outcome of calculations based on a constructive interference of body waves in a surface layer is that the phase velocity is dependent on the propagation direction. Both arguments are summarized and an error in the calculations giving dependence is pointed out. The calculations and observations of surface wave amplitude changes in laterally inhomogeneous media are also summarized. 相似文献
17.
How a wave interacts with heterogeneous media has been pursued by many geophysicists.The complexity of subsurface heterogeneities is seismologically a relative concept to wavelengths of seismic waves.A growing perception is that velocity variations,propagation angles,and computational accuracies are closely related at a variety of scales.A tentative strategy to quantitatively evaluate the complexity of subsurface heterogeneous media is presented in this article to see what scales of geological heterogeneiti... 相似文献
18.
为利用sPn与Pn波的走时差测定震源深度,进一步提高地震震源深度的测定精度,推导多层介质下sPn与Pn波的走时差与震源深度的关系,发现走时差与震中距无关,只与震源深度及区域地壳速度模型有关。震源在同一层中,走时差曲线的斜率不变,而当震源位于不同层中时,sPn-Pn走时差曲线的斜率不同,并呈分段直线的走时差曲线形态。地壳速度结构纵向越不均匀,多层和单层介质下利用sPn-Pn走时差计算的震源深度误差就越大,走时曲线的各分段直线斜率相差越大;探讨地壳中sPn与Pn波传播路径相同但波速不同的单层地壳速度模型,发现单层介质下波速越大,测定的震源深度越大;对于同一地区相同的地壳分层结构,测得的震源深度随着泊松比的增大而减小。基于前人给出的中国五个典型块体多层平均地壳模型,给出sPn-Pn走时差与震源深度计算公式速查表。 相似文献
19.
Ambient seismic noise or microtremor observations used in spatial auto-correlation (SPAC) array methods consist of a wide frequency range of surface waves from the frequency of about 0.1 Hz to several tens of Hz. The wavelengths (and hence depth sensitivity of such surface waves) allow determination of the site S-wave velocity model from a depth of 1 or 2 m down to a maximum of several kilometres; it is a passive seismic method using only ambient noise as the energy source. Application usually uses a 2D seismic array with a small number of seismometers (generally between 2 and 15) to estimate the phase velocity dispersion curve and hence the S-wave velocity depth profile for the site. A large number of methods have been proposed and used to estimate the dispersion curve; SPAC is the one of the oldest and the most commonly used methods due to its versatility and minimal instrumentation requirements. We show that direct fitting of observed and model SPAC spectra generally gives a superior bandwidth of useable data than does the more common approach of inversion after the intermediate step of constructing an observed dispersion curve. Current case histories demonstrate the method with a range of array types including two-station arrays, L-shaped multi-station arrays, triangular and circular arrays. Array sizes from a few metres to several-km in diameter have been successfully deployed in sites ranging from downtown urban settings to rural and remote desert sites. A fundamental requirement of the method is the ability to average wave propagation over a range of azimuths; this can be achieved with either or both of the wave sources being widely distributed in azimuth, and the use of a 2D array sampling the wave field over a range of azimuths. Several variants of the method extend its applicability to under-sampled data from sparse arrays, the complexity of multiple-mode propagation of energy, and the problem of precise estimation where array geometry departs from an ideal regular array. We find that sparse nested triangular arrays are generally sufficient, and the use of high-density circular arrays is unlikely to be cost-effective in routine applications. We recommend that passive seismic arrays should be the method of first choice when characterizing average S-wave velocity to a depth of 30 m (Vs30) and deeper, with active seismic methods such as multichannel analysis of surface waves (MASW) being a complementary method for use if and when conditions so require. The use of computer inversion methodology allows estimation of not only the S-wave velocity profile but also parameter uncertainties in terms of layer thickness and velocity. The coupling of SPAC methods with horizontal/vertical particle motion spectral ratio analysis generally allows use of lower frequency data, with consequent resolution of deeper layers than is possible with SPAC alone. Considering its non-invasive methodology, logistical flexibility, simplicity, applicability, and stability, the SPAC method and its various modified extensions will play an increasingly important role in site effect evaluation. The paper summarizes the fundamental theory of the SPAC method, reviews recent developments, and offers recommendations for future blind studies. 相似文献
20.
面波成像是研究地壳上地幔横波速度结构的一种重要方法．通常,面波相速度或群速度成像假设面波沿大圆路径传播．但是,在地下介质速度结构变化较大时,面波会偏离大圆路径传播,从而导致基于大圆路径假设下的面波成像结果存在一定的误差. 我们采用基于射线追踪的面波成像方法,研究了面波的偏离大圆路径传播对四川西部地区面波相速度成像结果的影响．使用快速行进法(fast marching method)进行面波传播路径的射线追踪,采用子空间反演法(subspace inversion)进行迭代反演,对理论模型合成数据和川西台阵的短周期背景噪声相速度频散数据进行成像分析,并与使用大圆路径传播的成像结果进行对比．对理论模型的测试结果表明,当速度结构变化较大时,基于偏离大圆路径传播的面波成像能够更好地恢复模型异常．对川西台阵的真实数据反演结果显示:在短周期为6 s时,基于偏离大圆路径传播的反演方法较基于大圆路径传播的反演方法所获得的相速度异常的幅度更大些,在四川盆地区域两者的差异接近0.2 km/s;在周期为10 s时,两种反演方法的差异显著减小,基本都在0.1 km/s以内．这主要是因为6 s周期的面波相速度对复杂的上地壳浅层结构更为敏感,从而使得面波的偏离大圆路径传播效应对反演结果的影响更为显著．本文结果表明,当某一周期不同路径的面波相速度测量值变化较大,例如相对于平均相速度的异常超过10％时,则需考虑采用基于偏离大圆路径传播的面波成像方法,否则速度异常较大区域的反演结果可能会造成较大的偏差． 相似文献