The very low-frequency step-frequency GPR system and its application to active fault detection

Ground-penetrating radar (GPR) in the high-frequency range is subject to attenuation, which limits its application in many fields, such as underground water detection and other near-surface geological studies. We built a very low-frequency GPR system based on a vector network analyser (VNA) and developed the system controlling software using visual basic for application (VBA). We also built a wire-line antenna with a central frequency of 10 MHz on the ground. Results from an experiment on a water reservoir dam showed that the system works well. Active fault evaluation is important for city planning and construction. The soil layer in Changchun City, Northeast China, has low-resistivity and a depth of 10-20 metres. It is difficult for conventional GPR systems to detect bedrock in Changchun City. In this paper, we investigate the active fault in Changchun City using the very low-frequency step-frequency GPR system. The results from the step-frequency GPR shows clearly the undulation of the bedrock. From this and the resistivity soundings we are able to interpret the location and the depth of the fault.