最小二乘傅立叶有限差分偏移

一般偏移算法是用反演算子通过解析方法求解.最小二乘偏移方法采用另一种思路,即采用数值方法,通过解一个线性离散反问题来索求解.这样我们试着寻找一个模型匹配地震数据并能表现出其某些特点来得到偏移图像.最小二乘法能减少偏移赝像,得到更精确的偏移效果.Kirchhoff算子在最小二乘偏移方法中应用较广,但需要较多的迭代次数,而且具有Kirchhoff偏移的缺点.本文把最小二乘方法运用到基于波长延拓的波动方程偏移方法中,为提高最小二乘偏移的效率,可采用效率较高的正传播算子和反传播算子.我们利用效率较高,能适应剧烈横向变速的傅立叶有限差分正传播和反传播算子来做叠后最小二乘偏移.数值实例表明,通过少数的共轭梯度法迭代,就能得到与真实模型差别很微小的偏移效果.对于傅式变换我们采用了数值软件FFTW,其变换速度比常规FFT算法一般要快六倍以上,进一步提高了效率.本文算法很容易在并行机上实现,这些特点在处理大型数据时大有裨益.     

Visco-acoustic transmission waveform inversion of velocity structure in space-frequency domain

According to the least square criterion of minimizing the misfit between modeled and observed data,this paper provides a preconditioned gradient method to invert the visco-acoustic velocity structure on the basis of using sparse matrix LU factorization technique to directly solve the visco-acoustic wave forward problem in space-frequency domain.Numerical results obtained in an inclusion model inversion and a layered homogeneous model inversion demonstrate that different scale media have their own frequency ...     

Problematic non-double-couple mechanism of the 2002 Amfilochia Mw5 earthquake, Western Greece

Two seismic agencies reported a very low double-couple percentage (DC%) of the Amfilochia earthquake, of about 30% and 60%, by Schweizerischer Erdbebendienst and Mediterranean Very Broadband Seismographic Network, respectively. Near-regional waveforms, carefully analyzed in this paper for the DC%, suggested a higher DC%, ranging from 75 to 100, dependent on the uncertainty of the source position (optimum value DC% = 93). Using a statistical F test, forward modeling of the near-regional data with a single-event low-DC% source yields a significantly worse waveform match. The fit of near-regional data can be further improved (although at the 90% significance level only) when considering a speculative two-event model. The same model, when viewed at the very-low frequency range, reaches the very low DC% values. However, two features make the two-event model unlikely: The two subevents strongly differ in their focal mechanism, and their mutual separation (3.5 s) is larger than the expected duration of this earthquake. Therefore, the two-source model appears to be nothing but an interesting equivalent representation of the non-DC model, providing some insight into the possible origin of the apparently low DC%. Preference is given to the simple interpretation, most clearly supported by the near-regional data, that the Amfilochia earthquake was an almost pure-shear event.     

基于熵权-IOWGA算子的变权组合预测新方法

针对熵权法组合权重分配固定不变的问题,提出一种基于IOWGA算子的权重分配方法,建立基于熵权-IOWGA算子的变权组合模型。该方法以各单一模型的预测精度作为诱导值,按每一期诱导值的大小对单一模型进行有序赋权,并将其应用到变形数据分析中。实验表明,该方法赋权过程合理,模型预测精度更高,更加适用于变形分析预测过程。     

地震盲反褶积综述

从动态系统角度对地震勘探中盲反褶的有关问题进行分析,将线性与非线形地震盲反褶积纳入盲系统辨识的统一框架．综述了几种重要地震盲反褶积方法的原理与效果．指明起源于瞬时混合盲反褶积(或盲源分离)的独立分量分析(ICA)方法在解决一般化地震盲反褶积问题上的重要应用前景,并给出两种可能的解决方案．     

Estimation of the Source Time Function Based on Blind Deconvolution with Gaussian Mixtures

It is demonstrated that the blind deconvolution method is fully capable of recovering the unknown Greens function and of estimating the source time functions from observed seismic data of small earthquakes. Based on the assumption of the Gaussian-mixture model of the Greens function, the newly-formulated algorithm is evaluated using synthetic seismic data along with those of the May 8, 1996 Mexico earthquake (M_c = 4.6). Since the estimated results closely match the theoretical input very well, the method is then employed to analyze the source time functions of the July 7, 1995 Pu-Li, Taiwan earthquake (M_L = 5.3). The stations triggered by this event were azimuthally well covered. Using the estimated source time functions, information pertaining to the directivity effect is readily obtained, and the actual fault plane of this event is identified, thus clearly indicating that this method provides a most efficient way to estimate the source time function of a small earthquake.Acknowledgment The authors would like to express their thanks to two anonymous reviewers for their valuable suggestions and Dr. I. Santamarias courteous assistance. They also appreciate the efforts of Drs. H.C. Chiu and R.J. Rau, who provided the seismic data and the fault plane solutions. The National Science Council, Taiwan, has supported this research (NSC 91-2119-M-194-011).     

THE USE OF A CROSS-CORRELATION TECHNIQUE TO ENHANCE JANSSON''S DECONVOLUTION PROCEDURE

The use of a cross-correlation prefiltering technique to enhance the ability of Jansson's iterativedeconvolution procedure to deconvolve extremely noisy chromatographic data is investigated.Test casesinclude peaks whose resolutions are as low as 0.35 and whose signal-to-noise ratios are as low as 1:1.Evaluation criteria include RMS error,relative peak error and peak area repeatability.For comparisonpurposes,relative peak area errors and peak area variances are also evaluated for noisy but well resolvedpeaks that have only been prefiltered with the cross-correlation filter.Jansson's method in conjunctionwith cross-correlation prefiltering is shown not only to resolve overlapped peaks but in some cases toimprove their signal-to-noise ratios.The study also establishes some limits to the capabilities of Jansson'smethod will regard to adverse data conditions.     

反插值法实现地球物理数据快速网格化

本文借鉴反演理论，采用反插值法实现地球物理数据的快速网格化.首先由已知点与未知网格点的反距离拓扑关系建立反演方程，用已知点值直接计算出其所在网格的未知网格点值，再利用Laplacian算子滤波，使得模型光滑，且能量最小化.利用预条件共轭梯度法求解网格化方程组，并结合螺旋坐标系思想和Wilson\|Burg谱分解法，将二维数据的滤波处理转换到一维空间进行处理，实现二维数据快速滤波.另外，引入了阻尼约束，保证求解稳定、迭代收敛.最后，应用该方法对合成数据和实际资料进行了试验.     

遥感图像边缘提取研究

本文在全面剖析基本遥感图像处理方法的基础上 ,提出了遥感图像边缘提取研究应重点考虑的几个因素。系统归纳了几种遥感图像边缘提取方法的特点 ,并结合实例分析了秘鲁 (Peru)NearNasca地区岩浆岩山脉边缘的提取。