We design synchronized double speckle-visibility spectroscopy (SVS) equipment to measure the particle rearrangements within the passive layer of granular flows in a rotating drum. We determine that the particle rearrangements within the passive layer are triggered by granular avalanches occurring in the active layer. Particle rearrangements exhibit alternating small and large pairs, and a statistical analysis demonstrates that they satisfy a power-Gaussian distribution. Furthermore, it is determined that the spatial distribution of the granular temperatures within the passive layer is not symmetrical about the center of the drum, which is different from that in the active layer. These results indicate that particle rearrangements develop independently following a granular avalanche trigger. Both the granular temperature and rearrangement frequency increase with the increasing drum rotation speed, but the periodicity of the particle rearrangements becomes weak as the rotation speed increases. (C) 2016 Elsevier B.V. All rights reserved.