  In presence of impurities, ferromagnetic and ferroelectric domain walls slide
only above a finite external field. Close to this depinning threshold, they
proceed by large and abrupt jumps, called avalanches, while, at much smaller
field, these interfaces creep by thermal activation. In this work we develop a
novel numerical technique that captures the ultra-slow creep regime over huge
time scales. We point out the existence of activated events that involve
collective reorganizations similar to avalanches, but, at variance with them,
display correlated spatio-temporal patterns that resemble the complex sequence
of aftershocks observed after a large earthquake. Remarkably, we show that
events assembly in independent clusters that display at large scales the same
statistics as critical depinning avalanches. We foresee this correlated
dynamics being experimentally accessible by magneto-optical imaging of
ferromagnetic films.
