Upperplate deformation, large interplate earthquakes and relation to friction properties of continental and subduction megathrust

Abstract:

Geodetic and remote sensing techniques can now be used to monitor surface deformation associated to the seismic cycle on megathrust. In absence of large interplate earthquake, the measured strain is generally interpreted to reflect elastic deformation of the upper plate related to the pattern of locking, or equivalently ‘interseismic coupling’ of the megathrust. Assessing what fraction of the observed strain is really elastic and available to drive future interplate earthquakes is actually a most difficult problem. It can only be assessed based on an accurate knowledge of the structure and deformation of the upper plate. We will discuss this issue based on observations from the Himalaya and from some oceanic subduction zones. In both contexts, the structure and morphology of the upper plate strongly correlate with the pattern of locking. We infer that a fraction of interseismic strain is actually anelastic. For megathrust with rapid slip rates (>1cm/yr) the assumption that interseismic strain is elastic is probably correct to first order. In any case, the upper plate structure carries information about the megathrust frictional properties and the characteristics of potential interplate earthquakes.