Guanghe Liang

A 21-point finite difference scheme for 2D frequency-domain elastic wave modelling

The 21-point finite difference scheme for the frequency-space domain elastic wave forward modelling is designed through optimising the impedance matrix, especially calculating the spatial derivative terms and the mass acceleration terms of the elastic wave displacement equation as accurately as possible. Comparative tests show that the 21-point finite difference scheme is much better in grid dispersion, memory requirement, and computation time than the 9-point scheme and slightly better than the 25-point scheme. The 21-point finite difference scheme is ~15% lower in memory consumption and computing time than the 25-point scheme. The numerical examples show that the 21-point finite difference scheme is valid in the sense of the numerical simulation of ideal models.

Frequency-wavenumber implementation for P- and S-wave separation from multi-component seismic data

In this paper, we present a frequency-wavenumber domain scheme to separate P- and S-waves from multi-component seismic data at the free surface. Based on the relationship between the P- and S-wave separated elastic equation, and the divergence and curl operators, we modify the equation to make it applicable to surface seismic data. In the modified equation, the P-wavenumber is chosen to reject the P-waves, and the S-wavenumber is chosen to eliminate the S-waves. The changes in the P-S amplitude ratio caused by the wavenumber choice are corrected. For the free surface condition, an up-going wavefield separation filter is introduced into the modified equation, which can remove the free surface effects from the surface seismic data. In the case of a free surface exhibiting lateral heterogeneity, the seismic data are first transformed into the frequency domain using the fast Fourier transform (FFT), and then are transformed into the wavenumber domain using the discrete Fourier transform (DFT). In the second transform using the DFT, the modified equation is used to separate the P- and S-waves. Numerical tests on synthetic data for three models demonstrate the good performance and accuracy of the scheme.

A modified excitation amplitude imaging condition for prestack reverse time migration

In wave-equation-based migration, the imaging condition is an important factor that impacts migration accuracy and efficiency. Among the commonly used imaging conditions, the excitation amplitude imaging condition has high resolution, accuracy and low storage and input/output burden when compared with others. However, the excitation amplitude extracted by this imaging condition in its current form will produce a distorted migration image for certain scenarios. In this paper, a modified excitation amplitude imaging condition is proposed that addresses the above problem and produces migrated images free from distortion for complicated geologic models. In this paper, we propose a method to effectively use the modified shortest path method (MSPM) for extracting the maximum amplitude around the first-arrival events. Then, the excitation amplitude imaging condition is applied to obtain a continuous and clear migration image. This process can, to some extent, improve the distorted migration image produced by the traditional excitation amplitude imaging condition. Some numerical tests with synthetic data of Sigsbee2a and Marmousi-II models show that the improvement is feasible and effective in complex-structure media. We propose a process to effectively use the modified shortest path method for extracting the maximum amplitude around the first-arrival events. Then, the excitation amplitude imaging condition is applied to obtain a continuous and clear migration image. Numerical tests show that the improvement is feasible and effective in complex-structure media.

Zhengguang: A potentially large, high-grade epithermal gold deposit in the Duobaoshan metallogenic belt, Heilongjiang, northeastern China

Traditional ideas and methods are of limited use in deep prospecting in plant and volcanic-covered areas in Heilongjiang Province. The application of the authors’ ‘three-field anomaly interrestrain’ theory and a new geological-geophysical-geochemical prospecting technique combination has helped the local geological team to learn more about ore-controlling structural and metallogenic information under the cover. Subsequent drilling programs have revealed and assessed a potential large high-grade epithermal gold deposit in the southeastern part of the important porphyry copper belt.