  We image local structural rearrangements in soft colloidal glasses under
small periodic perturbations induced by thermal cycling. Local structural
entropy $S_{2}$ positively correlates with observed rearrangements in colloidal
glasses. The high $S_{2}$ values of the rearranging clusters in glasses
indicate that fragile regions in glasses are structurally less correlated,
similar to structural defects in crystalline solids. Slow-evolving high $S_{2}$
spots are capable of predicting local rearrangements long before the
relaxations occur, while fluctuation-created high $S_{2}$ spots best correlate
with local deformations right before the rearrangement events. Local free
volumes are also found to correlate with particle rearrangements at extreme
values, although the ability to identify relaxation sites is substantially
lower than $S_{2}$. Our experiments provide an efficient structural identifier
for the fragile regions in glasses, and highlight the important role of
structural correlations in the physics of glasses.
