Modelling and inversion of geophysical electromagnetic data

点击翻译按钮获取中文摘要

The goal of geophysics is to understand, and perhaps predict, the dynamic processes that move and shape the Earth beneath our feet, and to "look" into the Earth to see these processes in action, or their consequences. One technique for remotely sensing what the structure of the subsurface is, even to depths of tens of kilometres, uses electromagnetic fields. In this technique, electric currents are induced to flow in the rocks. The strength and disposition of the currents depend on rock type. Metallic ores, for example, are relatively good at conducting electricity. The induced currents in the ground give rise, in turn, to electromagnetic fields which can be measured. The strengths and variations of these measurements depend on the induced currents, and so on the rocks themselves. It is therefore possible to turn the measurements on their heads, that is, invert them, and extract information about what the rock types are in the subsurface. The proposed research determines to (i) improve the mathematics used by computer programs to predict what the induced currents would be if the rock types in the subsurface were known, and (ii) improve the programs that invert measurements of the electromagnetic fields to generate models of the structure of the Earth. Recent advances have produced what is effectively the first generation of these programs for fully three-dimensional models of the Earth. However, the mathematical representations these programs use for the arrangements of rock types in the subsurface are basic, being neither flexible enough to cope with the complicated structures that occur in nature, nor precise enough to handle the dramatic changes between adjacent rock types that can exist for certain important features such as ore deposits. This research programme will investigate the use of more sophisticated and refined representations of the subsurface to overcome these problems. The result will be computer programs that can provide more detailed and more reliable models, or "images", of the subsurface. These programs will be of use to the mining industry, enabling new ore deposits to be found. They will also be of use in remotely sensing groundwater resources, geotechnical applications, and in determining the deep structure of the Earth's crust.