Understanding natural and/or induced seismicity (a series of earthquakes of different magnitude) may require a multi-scale vision of fault heterogeneity. This talk consists of three parts. (1) Seismicity cycle – deterministic and probabilistic features, (2) Induced seismicity due to fluid circulation – fluid controlling and shear rupture domination, and (3) Scale dependent aseismic loading. The numerical simulations are carried out fully dynamically or quasi-statically using a boundary integral equation method (i.e. boundary element method). The basic concept given here is that the fracture energy of the interface is scale-dependent and hierarchically structured by spatial superposition. The models are able to produce a cascade-like rupture growth and spontaneous arrest, holding an earthquake scaling relation (constant stress drop over scales). Through these works, I would like to argue the mechanical causality in the earthquake complexity.