Instantaneous attributes for characterization of subsurface structures of an active fault by GPR

Several new faults are emerging near Ulaanbaatar city, the capital of Mongolia due to earthquakes. It becomes very important to investigate these faults. Ground penetrating radar (GPR) has been widely used in geologic, hydrogeologic, and civil engineering purposes. Correlated with geological exposures and trenches, GPR data can offer detail subsurface information to past earthquakes investigation. Instantaneous attributes include instantaneous amplitude, instantaneous phase and instantaneous frequency. As a measure of continuity of reflection events, instantaneous phase could reflect changes in lithology and stratigraphic sequence and identify discontinuities caused by faults. In this paper, we will describe the field experiment conducted in the Deren fault by GPR, data processing procedures, and using a simple geological model inferred from the instantaneous phase for data interpretation. The processed GPR data show details of subsurface information correlated to the fault. Many of the identified structures ranging from a few tens of centimeters to depths >10 m are not evident at the surface. Using surface-based observations from the geological trench, GPR should be a good tool to reveal complicated fault zone information such as location, dip and azimuth.