  In this study, we have investigated the fluctuations of particle motion, i.e.
the non-affine motion, during the avalanche process, discovering a rich
dynamics from the microscopic to the macroscopic scales. We find that there is
strong correlation between the magnitude of the velocity fluctuation and the
velocity magnitude in the spatial and temporal domains. The possible connection
between this finding and STZ is discussed based on the direct measurement of
the T1 events. In addition, the velocity magnitude of the system and the stress
fluctuations of the system are strongly correlated temporally. Our finding will
pose challenges to the development of more rigorous theories to describe the
avalanche dynamics based on the microscopic approach. Moreover, our finding
presents a plausible mechanism of the particle entrainment in a simple system.
