Under a slow external driving, out-of-equilibrium heterogeneous systems can respond in the form of collective excitations. This phenomenon covers a wide range of length scales from a few nanometers or millimeters all the way up to geological scales for earthquakes.These avalanches are usually measured in the time evolution of a global, bulk-averaged quantity, often referred to as crackling noise. For critical or near-critical systems, avalanches obey power-law probability distributions lacking a characteristic scale. Ideally, the goal is to extract information concerning the local dynamics, from analyzing the avalanches in the global observable. However, such a task is generally difficult, since the global dynamics involves local simultaneous avalanches, which could even be correlated.

We present an analysis of the dynamics of slowly driven fronts near the critical depinning transition. The goal is to relate local activity clusters to bursts in the global velocity time series. We characterize how local activity organizes spatiotemporally during a global burst depending on the distance to the critical depinning transition. New scaling relations connecting sizes and durations of avalanches at both description levels are, thus, established.