Revealing the shallow geometry of the Litang fault on the southeastern Qinghai-Tibet Plateau using multi-frequency ground Penetrating radar (GPR) profiles and trenching

Abstract

Subject to the severe and fragile natural environment on the Qinghai-Tibet Plateau, it was labour-intensive and time-consuming to obtain the detailed shallow geometry of the Litang fault for understanding the fault’s kinematics and characteristics using traditional methods. In this study, we presented a case study to investigate the detailed shallow geometry of the Litang fault using multi-frequency GPR profiles and trenching. The shallow geometry of active faults at variable depth with multi-spatial resolutions was revealed by multi-frequency GPR data. A deformation zone, two faults F1 and F2 and three stratigraphic units were identified in the 100 MHz GPR data, and the detailed subsurface information of the fault F1 was clearly discerned in the 250 MHz and 500 MHz GPR profiles with a better lateral and vertical resolution. In addition, the fault displacement of ∼ 0.2 m was verified in the 500 MHz GPR data through the interfaces of different stratigraphic units at the two flanks of the fault F1. The continuous horizontal radar reflections were bent downward when crossing the fault F1, and it indicated the fault F1 was dominated by the movement of the strike-slip fault with a thrust motion. A trenching section was implemented to provide additional information for better interpreting and understanding the GPR data. This study demonstrated that a combination of multi-frequency GPR profiles and trenching was suitable for depicting the detailed shallow geometry of the Litang fault on the Qinghai-Tibet Plateau, especially the geology conditions were complex or surface evidences were unobservable.