Applied Geophysics

In this paper we calculate a synthetic medium surface displacement response that is consistent with real measurement data by applying the least-square principle and a niche genetic algorithm to the parameters inversion problem of the wave equation in a two-phase medium. We propose a niche genetic multi-parameter (including porosity, solid phase density and fluid phase density) joint inversion algorithm based on a two-phase fractured medium in the BISQ model. We take the two-phase fractured medium of the BISQ model in a two-dimensional half space as an example, and carry out the numerical reservoir parameters inversion. Results show that this method is very convenient for solving the parameters inversion problem for the wave equation in a two-phase medium, and has the advantage of strong noise rejection. Relative to conventional genetic algorithms, the niche genetic algorithm based on a sharing function can not only significantly speed up the convergence, but also improve the inversion precision.

The development of Tongchuan City, Shaanxi Province, located in the northwestern region of China, is restricted by water resources. The direct current resistivity and induced polarization sounding methods are typically applied in finding urban groundwater. These methods, however, are not effective due to their complicated topography and geological conditions. The application practice shows that the audio magnetotelluric (AMT) method has a large depth of exploration, high work efficiency, and high lateral resolution. To investigate the distribution of groundwater resources, we deployed three audio-frequency magnetotelluric profiles in the city area. The impedance tensor information of AMT data is obtained using SSMT2000. AMT data dimension analysis reveals that the two-dimensional structural features of the observation area are obvious. The main structure of the observation area is about 45° northeast, as indicated by structural trend analysis. A shallow two-dimensional electrical profile of 1 km in Tongchuan City is obtained by two-dimensional nonlinear conjugate gradient inversion. Finally, combined with regional geological information, the geological structure characteristics reflected by the electrical profile were obtained along with the detailed characteristics of water-rich structures in the area. The influence of the structure on the groundwater distribution was analyzed, and the water-rich areas were identified. This work contributes to the prospective development of Tongchuan City.

Full waveform inversion (FWI) is an extremely important velocity-model-building method. However, it involves a large amount of calculation, which hindsers its practical application. The multi-source technology can reduce the number of forward modeling shots during the inversion process, thereby improving the efficiency. However, it introduces cross-noise problems. In this paper, we propose a sparse constrained encoding multi-source FWI method based on K-SVD dictionary learning. The phase encoding technology is introduced to reduce crosstalk noise, whereas the K-SVD dictionary learning method is used to obtain the basis of the transformation according to the characteristics of the inversion results. The multi-scale inversion method is adopted to further enhance the stability of FWI. Finally, the synthetic subsag model and the Marmousi model are set to test the effectiveness of the newly proposed method. Analysis of the results suggest the following: (1) The new method can effectively reduce the computational complexity of FWI while ensuring inversion accuracy and stability; (2) The proposed method can be combined with the time-domain multi-scale FWI strategy flexibly to further avoid the local minimum and to improve the stability of inversion, which is of significant importance for the inversion of the complex model.

Accurate displacement prediction is critical for the early warning of landslides. The complexity of the coupling relationship between multiple influencing factors and displacement makes the accurate prediction of displacement difficult. Moreover, in engineering practice, insufficient monitoring data limit the performance of prediction models. To alleviate this problem, a displacement prediction method based on multisource domain transfer learning, which helps accurately predict data in the target domain through the knowledge of one or more source domains, is proposed. First, an optimized variational mode decomposition model based on the minimum sample entropy is used to decompose the cumulative displacement into the trend, periodic, and stochastic components. The trend component is predicted by an autoregressive model, and the periodic component is predicted by the long short-term memory. For the stochastic component, because it is affected by uncertainties, it is predicted by a combination of a Wasserstein generative adversarial network and multisource domain transfer learning for improved prediction accuracy. Considering a real mine slope as a case study, the proposed prediction method was validated. Therefore, this study provides new insights that can be applied to scenarios lacking sample data.

The positive and negative difference of deep and shallow resisitivity in formation without invasion is caused mainly by the fixed two tool constants from numerical simulations. A dynamic calibration method for tool constants is proposed based on the effects of the mud and formation resisitivity ratio on the two constants calculated using the finite element method (FEM). Finally, four specific examples are given to validate the dynamic calibration method. It is an automatic borehole correction method and can give more accurate formation resistivity. The method is useful for dual laterolog logging.

In this paper, we review the differences between velocity geophones (VG) and acceleration geophones (AG) and their effect on seismic signals acquired in onshore-offshore transition areas. We present a new generation of Land Piezoelectric Geophone (LPG) and analyze its performance. Our field experiments demonstrate that our new LPG can be used to substitute for VGs in order to eliminate phase, frequency and energy differences between different geophone systems commonly used in transition areas.