Fore‐arc deformation controls frequency‐size distribution of megathrust earthquakes in subduction zones

Seismotectonic deformation in subduction zones seems to follow rather simple spatiotemporal patterns with fore‐arc basins overlying the areas of large slip during quasiperiodic megathrust earthquakes. To study the possible coupling between long‐term deformation and earthquake behavior, we use compressive granular wedges overlying a rate‐ and state‐dependent frictional interface as analogue models of subduction zone fore arcs overlying a seismogenic megathrust. For different seismogenic zone geometries, we analyze deformation time series with respect to the accumulation of permanent strain and frequency‐size distributions of episodic slip events equivalent to great ( M > 8) earthquakes. We observe that permanent deformation in the wedges localizes at the periphery of unstable slip at depth over tens of simulated seismic cycles. For updip‐limited seismogenic zone models, this leads to structural wedge segmentation characterized by an elastic domain overlying the zone of unstable basal slip. Along with the evolution of segmentation the frequency‐size distributions of episodic slip events develop from more random, Gutenberg‐Richter‐like events ( b value ∼0.6) toward more periodic, characteristic events ( b value <0.1). Corresponding coefficients of variation ( C v ) of recurrence intervals decrease from C v ≈ 0.6 in deforming wedges to C v ≈ 0.3 in segmented wedges. From the experiments we thus infer a positive feedback between fore‐arc tectonics and megathrust seismogenesis which brings the system from a stochastic to a more deterministic state. Our experimental observations imply that the quasiperiodic recurrence of great subduction earthquakes evident from existing earthquake records is a long‐term feature intrinsically related to the seismotectonic segmentation of the fore‐arc wedges.