Borehole Electromagnetic Imaging and Its Application in Karst Exploration
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摘要: 井间电磁波层析成像技术是将医学CT应用于地球物理学中的一项新技术,它主要依据电磁波在不同介质中传播时的吸收差异,重建井间介质吸收系数的分布图像,形象及直观地展现研究区域的地质结构。本文详细地研究了井间电磁波层析成像技术的基本原理,对具有高低吸收电磁异常体的理论模型,根据一定的观测系统对电磁波的场强进行了数值模拟,并采用SIRT反演技术对吸收异常体的图像进行了重建;同时将该方法应用于广西某地拟建桥址的岩溶勘查之中,取得了良好的应用效果。Abstract: The borehole electromagnetic imaging technique is an advanced geophysical technology which is based upon the theory of medical CT to reconstruct the geological structure according to the absorption coefficients of the electromagnetic waves, and then reconstructs geological structure between the boreholes. In this paper, the method is discussed theoretically and computationally in detail for the different models, including low- and high-attenuation anomalies, and the inversion of the large-spare linear equations were solved by the Simultaneous Interactive Reconstructive Technique (SIRT) for the synthetic models to reconstruct the electromagnetic anomalies. Finally the method was applied to the observed data acquired in field to investigate the foundation of a to-be-built bridge in Guangxi province, and the result shows a few possible Karst caves which are fine consistent with the drilling data.
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Keywords:
- borehole electromagnetic imaging /
- absorption coefficient /
- SIRT /
- Karst exploration
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