Fault controls on spatial variation of fracture density and rock mass strength within the Yarlung Tsangpo Fault damage zone (southeastern Tibet)

Abstract

Recent technological developments including Unmanned Aerial Vehicles, terrestrial laser scanning, photogrammetry and point cloud analysis software tools greatly enhance our ability to investigate the relationship between faulting and the spatial geometrical and mechanical characteristics of a rock mass controlled by faulting. Using the Yarlung Tsangpo (YLTP) Fault of southeastern Tibet as a case study, we propose the procedures, investigation approaches, evidence and criteria for quantitatively defining the threshold distance for damage zones combining the spatial variations of fracture density, rock mass strength and rockfall inventory in this study. Based on the study, the extent of threshold distance of damage zone of the YLTP Fault is estimated as 5.9 ± 0.6 km, which has been compared with published data from the evidence of thermal effects related to exactly the same fault and shows a good match. Five predominant joint sets were identified in the study area. Influenced by tectonics, the relationship between mean spacing of the joint sets with distance from the fault core shows a strong positive power relationship. It is consistent with the result of the exponential relation between the mean size of fallen blocks and distance from the fault core that is obtained independently. We conclude that fracture density (the joint volumetric count, Jv) and cohesion of the rock mass show power curve relations with distance within the damage zone. The fault first affects the characteristics of rock mass structures, and then the characteristics of the rock structures influence the stability of slope leading to rockfall.