A hybrid indirect boundary element—discrete wave number method applied to simulate the seismic response of stratified alluvial valleys     

S. A. Gil-Zepeda  J. C. Montalvo-Arrieta  R. Vai  F. J. Snchez-Sesma 《Soil Dynamics and Earthquake Engineering》2003,23(1):77-86

A hybrid indirect boundary element – discrete wavenumber method is presented and applied to model the ground motion on stratified alluvial valleys under incident plane SH waves from an elastic half-space. The method is based on the single-layer integral representation for diffracted waves. Refracted waves in the horizontally stratified region can be expressed as a linear superposition of solutions for a set of discrete wavenumbers. These solutions are obtained in terms of the Thomson–Haskell propagators formalism. Boundary conditions of continuity of displacements and tractions along the common boundary between the half-space and the stratified region lead to a system of equations for the sources strengths and the coefficients of the plane wave expansion. Although the regions share the boundary, the discretization schemes are different for both sides: for the exterior region, it is based on the numerical and analytical integration of exact Green's functions for displacements and tractions whereas for the layered part, a collocation approach is used. In order to validate this approach results are compared for well-known cases studied in the literature. A homogeneous trapezoidal valley and a parabolic stratified valley were studied and excellent agreement with previous computations was found. An example is given for a stratified inclusion model of an alluvial deposit with an irregular interface with the half-space. Results are displayed in both frequency and time domains. These results show the significant influence of lateral heterogeneity and the emergence of locally generated surface waves in the seismic response of alluvial valleys.  相似文献   

Continuous wavelet-like filter for a spherical surface and its application to localized admittance function on Mars     

Motoyuki Kido  David A. Yuen 《Physics of the Earth and Planetary Interiors》2003,135(1):1-16

We have developed a 2D isotropic continuous wavelet-like transform for a spherical surface. The transform is simply defined as the surface convolution between the original field and a kernel, based on the zeroth-order Bessel function with a spherical correction. This spherical correction violates the geometric similarity for the various scales of the kernels, which becomes more apparent at longer wavelengths. We found numerically that this transform is practically equivalent to a Gaussian bandpass filter in the spherical harmonic domain. We have applied this wavelet-like transform on the recently acquired Martian gravity and topography fields. Using a ratio constructed locally from these two fields, we have constructed a map describing the lateral variations of the localized admittance function on Mars.  相似文献   

荒漠戈壁下垫面表面动量和感热湍流通量参数化研究   总被引：9，自引：0，他引：9  

ZHANG Qiang  HUANG Ronghui  TIAN Hui 《大气科学进展》2003,20(1):111-118

用合理筛选以后的野外观测资料，研究了荒漠戈壁地表湍流通量参数化的问题。首先，分析了Monin-obukhov相似函数的特征，并拟台出了其经验公式。结果表明，风速和温度相似性函数随稳定度参数的变化曲线与典型经验曲线差异较小，并且在经验曲线分布范围以内，但中性时的值有所不同。同时，还用该资料给出了动量和标量粗糙度(感热粗糙度)长度的平均值及其标量粗糙度随摩擦速度的变化关系。发现标量粗糙度的平均值大约比动量粗糙度的小一个量级，并且随摩擦速度的增大而减小，但明显比其理论预测值要大。  相似文献   

小波变换在识别储层流体性质中的应用   总被引：16，自引：0，他引：16       下载免费PDF全文

岳文正  陶果 《地球物理学报》2003,46(6):863-869

根据小波变换的特点提出一种识别储层流体的新方法. 本文假设测井所得的信号为地层微观孔隙结构、地层流体性质及岩性和岩相等各部分的综合贡献之和，不同的储层中小波分析的能量谱特征不同，因而通过对已知储层模型进行小波能量谱分析，可得到各种储层的特征能量谱，根据这些储层特征能量谱就可以对待划分的储层段进行储层流体性质判别.  相似文献   

基于小波变换的动态地震活动周期分析   总被引：25，自引：0，他引：25  

杜兴信 《地震》1997,17(3):257-264

利用Ｍｏｒｌｅｔ小波变换对华北、中国大陆和陕西的地震活动进行了动态周期分析。结果表明，地震活动既存在比较稳定的周期，也有一定时变性，如华北近５００ａ来存在比较稳定的３００ａ周期和６０ａ左右周期，陕西近２０ａ来存在比较稳定的２￣３ａ周期，中国大陆５级以上地震在１９１０￣１９８０年普遍存在３０ａ左右周期，但在１９８０年后变为２０ａ左右周期，小波分析揭示的地震活动周期时变性，一方面提示在依据周期规律外推  相似文献   

中国重力异常的小波变换与多尺度分析   总被引：111，自引：19，他引：111       下载免费PDF全文

侯遵泽  杨文采 《地球物理学报》1997,40(1):85-95

阐述了小波变换及多尺度分析方法的原理，利用二维小波多尺度分析方法对中国布格重力异常进行了分解，并从其中划分出有意义的剩余异常．模型结果证明方法有效．由于本文方法可以将重力异常分解成各种几何尺度意义下的不同成分，这为重力解释和研究地壳的结构提供更多更新的依据．  相似文献   

ON THE VERTICAL DISCRETIZATION OF ATMOSPHERIC MODELS-PART Ⅰ:EXISTING PROBLEMS,DATA PROCESSING AND CHOICE OF VERTICAL COORDINATE AND BASIS FUNCTIONS     

Liao Dongxian  Zhu Yanqiu 《Acta Meteorologica Sinica》1997,11(2):187-195

Discussions are carried out on the vertical discretization of current atmospheric models.It is pointed out that there exist problems in the integration of the hydrostatic equation and the computation of vertical advection,vertical diffusion and so on.Then some possible ways for solving or alleviating them are suggested.Finally,the choice of vertical coordinate and basis functions is discussed.  相似文献   

Centroid moment tensor inversion of low-frequency seismic spectra using Green's functions for aspherical earth models     

Tatsuhiko Hara 《Geophysical Journal International》1997,130(1):251-256

We present a new method for centroid moment tensor (CMT) inversion, in which we employ the Green's function computed for aspherical earth models using the Direct Solution Method. We apply this method to CMT inversion of low-frequency seismic spectra for the 1994 Bolivia and 1996 Flores Sea deep earthquakes. The estimated centroid locations agree well with those obtained by multiple-shock analyses using body-wave data. This shows that it is possible to obtain reliable CMT solutions by analyses of low-frequency seismic spectra using accurate Green's functions computed for present 3-D earth models.  相似文献   

Source investigation of a small event using empirical Green's functions and simulated annealing     

F. Courboulex  J. Virieux  A. Deschamps  D. Gibert  A. Zollo 《Geophysical Journal International》1996,125(3):768-780

We propose a two-step inversion of three-component seismograms that (1) recovers the far-field source time function at each station and (2) estimates the distribution of co-seismic slip on the fault plane for small earthquakes (magnitude 3 to 4). The empirical Green's function (EGF) method consists of finding a small earthquake located near the one we wish to study and then performing a deconvolution to remove the path, site, and instrumental effects from the main-event signal.
The deconvolution between the two earthquakes is an unstable procedure: we have therefore developed a simulated annealing technique to recover a stable and positive source time function (STF) in the time domain at each station with an estimation of uncertainties. Given a good azimuthal coverage, we can obtain information on the directivity effect as well as on the rupture process. We propose an inversion method by simulated annealing using the STF to recover the distribution of slip on the fault plane with a constant rupture-velocity model. This method permits estimation of physical quantities on the fault plane, as well as possible identification of the real fault plane.
We apply this two-step procedure for an event of magnitude 3 recorded in the Gulf of Corinth in August 1991. A nearby event of magnitude 2 provides us with empirical Green's functions for each station. We estimate an active fault area of 0.02 to 0.15 km² and deduce a stress-drop value of 1 to 30 bar and an average slip of 0.1 to 1.6 cm. The selected fault of the main event is in good agreement with the existence of a detachment surface inferred from the tectonics of this half-graben.  相似文献   

Frequency-dependent relocation of the 1992 Nicaragua slow earthquake: an empirical Green's function approach     

Pierre F. Ihmlé 《Geophysical Journal International》1996,127(1):75-85

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