Résumé
The majority of the largest subduction megathrust earthquakes share the common characteristic of rupturing more than one asperity along the strike of the margin. Understanding the factors controlling the process of asperities synchronization, and thus maximum magnitude, is central for seismic hazard assessment. To investigate the role of asperities size and spacing on maximum magnitude, seismic rate and percentage of synchronized ruptures, we use analog models simulating a frictionally segmented megathrust. Analog models feature realistic tectonic loading, spontaneous (analog) earthquakes nucleation and propagation, and realistic 4D boundary conditions (i.e., wedge-like geometry and presence of a free surface, gravity, time and space continuum). The monitoring of model deformation and rupture kinematics is performed with the Particle Image Velocimetry technique. We found negative correlations between the barrier-to-asperity length ratio Db/Da and maximum magnitude and seismic rate. Db/Da also controls the process of asperities synchronization along the megathrust. Under the adopted experimental conditions, a permanent barrier is observed for Db/Da>0.5. Comparing our experimental results to the historical seismicity, slip deficit rates and presence of forearc basins of Nankai Trough, we propose that the distribution of megathrust frictional heterogeneities likely explains the diversity of earthquakes that occurred there.