Deformation Heterogeneity Within an Accretionary Prism and its Instability Through Time; Insights From Sandbox Experiments and Particle Simulations

The formation of accretionary prisms at subduction margins can be modelled and examined by using analogue experiments and numerical simulations. We have conducted sandbox experiments and distinct element simulations, both of which approximate the geologic body as an assembly of particles. Such granular materials can appropriately model the brittle deformation of the upper crust thus have been widely used to examine fault-related structures. During the accretion process, the velocity and stress vectors are highly heterogeneous and unstable in the both experiments and simulations. Due to the brittle approximation of the models, the deformation can be characterised by frictional faulting. Such frictional faulting is generally controlled by a series of intermittent displacement, so-called O^stick-slipO motions. Since the stick-slip motions occur due to accumulation/release cycles of elastic energy along fault surfaces, the stress field should also be cyclically distorted. Provided that many faults in a prism, the stress field would presumably be affected by such distortion caused by each faulting event. The instability in the particle velocity and stresses would therefore due to the stick-slip behaviour of the faults. The velocity and stress variations in an actual accretionary prism are poorly investigated. The models shown in this paper can be applied to understand such natural instability in the geo-environment and this technique might be used as a prediction tool of geo-hazards in a near future.