Three-dimensional tensor controlled-source electromagnetic modeling based on the vector finite-element method

Scalar CSAMT is only suitable for measurements in one and two dimensions perpendicular to geological structures. For complex 3D geoelectric structure, tensor CSAMT is more suitable. In this paper, we discuss 3D tensor CSAMT forward modeling using the vector finite-element method. To verify the feasibility of the algorithm, we calculate the electric field, magnetic field, and tensor impedance of the 3D CSAMT far-zone field in layered media and compare them with theoretical solutions. In addition, a three-dimensional anomaly in half-space is also simulated, and the response characteristics of the impedance tensor and the apparent resistivity and impedance phase are analyzed. The results suggest that the vector finite-element method produces high-precision electromagnetic field and impedance tensor data, satisfies the electric field discontinuity, and does not require divergence correction using the vector finite-element method.

水利水电工程中地质勘测及其技术应用

随着水利水电工程的发展,地质勘测技术在工程设计、施工和运营中扮演着日益重要的角色。本文首先介绍了基础的地质勘测方法,如地震反射法、钻孔勘探和地电阻法,及其在实际工程中的应用。接着,文章深入探讨了高级地质勘测技术,包括地质雷达、地球物理测井技术和三维地质建模,以及这些技术为水电工程带来的优势。最后,从数据解析的角度,探讨了地质勘测数据如何影响工程设计,以及工程实例中的实际应用。本文旨在为工程师和研究者提供一个对地质勘测技术在水利水电工程中应用的全面概览。

2.5D forward modeling and inversion of frequency-domain airborne electromagnetic data

Frequency-domain airborne electromagnetics is a proven geophysical exploration method.Presently,the interpretation is mainly based on resistivity-depth imaging and onedimensional layered inversion;nevertheless,it is difficult to obtain satisfactory results for two- or three-dimensional complex earth structures using 1D methods.3D forward modeling and inversion can be used but are hampered by computational limitations because of the large number of data.Thus,we developed a 2.5D frequency-domain airborne electromagnetic forward modeling and inversion algorithm.To eliminate the source singularities in the numerical simulations,we split the fields into primary and secondary fields.The primary fields are calculated using homogeneous or layered models with analytical solutions,and the secondary（scattered） fields are solved by the finite-element method.The linear system of equations is solved by using the large-scale sparse matrix parallel direct solver,which greatly improves the computational efficiency.The inversion algorithm was based on damping leastsquares and singular value decomposition and combined the pseudo forward modeling and reciprocity principle to compute the Jacobian matrix.Synthetic and field data were used to test the effectiveness of the proposed method.

Control of combustion area using electrical resistivity method for underground coal gasification

Underground coal gasification （UCG） is one of the clean technologies to collect heat energy and gases （hydrogen, methane, etc.） in an underground coal seam. It is necessary to further developing environ- mentally friendly UCG system construction. One of the most important UCG＇s problems is underground control of combustion area for efficient gas production, estimation of subsidence and gas leakage to the surface. For this objective, laboratory experiments were conducted according to the UCG model to iden- ti[y the process of combustion cavity development by monitoring the electrical resistivity activity on the coal samples to setup fundamental data for the technology engineering to evaluate combustion area. While burning coal specimens, that had been sampled from various coal deposits, electrical resistivity was monitored. Symmetric four electrodes system （ABMN） of direct and low-frequency current electric resistance method was used for laboratory resistivity measurement of rock samples. Made research and the results suggest that front-end of electro conductivity activity during heating and combusting of coal specimen depended on heating temperature. Combusting coal electro conductivity has compli- cated multistage type of change. Electrical resistivity method is expected to be a useful geophysical tool to for evaluation of combustion volume and its migration in the coal seam.

The spatial distribution characteristics of shallow fissures of a landslide in the Wenchuan earthquake area

Shallow fissures, being the main infiltration paths of fluid on the surface of a slope, played an important role in the whole process of a landslide. However, the spatial distribution characteristics of fissures in the slope are difficult to be determined. In this study, we attempted to characterize the variation pattern of slope fissures along depth in the Wenchuan earthquake area in Sichuan Province by combining engineering geological investigation, geomorphologic analysis and geophysical investigation. The geophysical methods that were used in this study include Multichannel Analysis of Surface Wave(MASW), Ground Penetrating Radar(GPR) and Electrical Resistivity Tomography(ERT). The results suggested that geophysical parameters(shear wave velocity, electromagnetic signals attenuation and resistivity) could provide valuable information for the spatial network of shallow fissures. Through the verification by engineering geological survey and geophysical sensitivity analysis, this work highlighted that MASW was the most appropriate technique to delineate the propagation of shallow fissures in a gravel soil slope.

Monitoring the Morphology of the Bottom of Streams and Reservoirs Using Electrical Impedance Spectrometry Method

A part of the Earth＇s surface has been formed by the action of running water during geomorphological development. The flow of water is one of the ways of how particles can be eroded, transported and accumulated. If endogenous processes do not work, the surface of the continents would lower to the level close to the ocean surface and the relief would have almost no ruggedness. Recently, there have been talks about the relative classification of deviation of the present state from the ＂original＂ or ＂natural＂ one caused by anthropogeneous effects. The activity of man can manifest itself by pollution, the excessive use of water, a change in the flow regime, and the like. Research into the morphology of the river bottom and the bottom of settling tanks or dam reservoirs is systematically carried out in selected streams and reservoirs by the long-term sampling of bottom sediments. The knowledge of the sediment layer is also important. The EIS method, which was used for measuring, is new for the aforementioned applications. Possibilities of EIS method with new apparatus using for this application were tested in laboratory and in situ. On the basis of interpretation of the electrical conductivity data, a grid of depth data was acquired. These data are characterized by anomalously high and low ＂spots＂ and show morphological changes in the studied area.