GPR measurements to assess the characteristics of active faults in Mongolia: GPR and active faults in Mongolia

摘要

In this paper we present the GPR results obtained on Emeelt and Songino faults in the vicinity of Ulaanbaatar, Mongolia. The objective is to understand the geometry, type of displacements and amplitude of these faults. The 2D and pseudo-3D GPR profiles are measured by using the 50, 250 and 500 MHz antennas. An appropriate processing of the GPR data, including the topographic migration, allows us to bring out indirect characteristics of these faults. The 500 MHz GPR profiles show a good consistency with the trenches observation, dug next to the pseudo-3D surveys on Emeelt fault. The 3D GPR imaging of a paleo-channel crossed by the Emeelt fault allows us to estimate its lateral displacement (of about 2 m) associated to its activity. It is consistent with a right lateral strike-slip displacement induced by an earthquake of magnitude around 7 or several of magnitude at least around 6. The 250 MHz GPR images of Songino fault show clear vertical apparent displacement of 1.3 m of radar reflections but it does not correspond to real displacement, as the fault is also associated with a strike slip component. GPR images indicate the presence of sedimentary deposits, potentially datable and affected by previous earthquakes.