ESR11

Project Title: Topographic signals from the shallow megathrust seismic cycle

Supervisor: Onno Oncken, Matthias Rosenau

Objectives: In this project we focus on topographic effects of deformation processes related to megathrust earthquakes and their diagnostic continental uplift and subsidence patterns. The most spectacular of such processes are coseismic stress changes inducing almost instantaneous coastal uplift and subsidence, which are typically recovered slowly during the interseismic period. The spatial correlation of these transient topographic signals with bathymetric and topographic features (e.g. the outer arc high, coastal and main cordillera) suggests that part of the seismic cycle deformation is not recoverable, i.e. that seismic cycle deformation in the lithosphere is elastoplastic. Moreover, active deformation of the overriding plate might feed back into the seismogenic process by controlling the stress state along the megathrust. The project will consider topographic signals from the megathrust seismic cycle and seismotectonic feedback on relevant time scales (from seconds to Millions of years) experimentally by means or analogue modelling. We plan to develop current “seismotectonic” analogue models of elastoplastic seismic cycles (Rosenau et al. 2009) into those involving a coupling between a viscoelastic asthenosphere and an elastoplastic lithosphere. This coupling will induce a wider range of deformation patterns beyond elastic seismic cycles to occur (e.g. upper plate shortening, buckling, pressure waves, isotatic response, mantle relaxation). Experimental observations will be benchmarked by analytical and numerical models and validated against nature.

Expected Results: Relationship between forearc anatomy and seismogenic behaviour.

Academic secondment: F. Funiciello (UniRoma3) 4 months, S. Willett (ETH Zürich) 3 months. Industry secondment: LaVision, 3 months for development of extension to StrainMaster tool for optical strain measurement.

Links to other projects: Close methodological and thematic links to ESR1, which investigates in a complimentary fashion dynamic topography due to deep sources (mantle flow). The project helps in explaining short term elastic deformation patterns in active subduction zones as investigated in ESR 12 and others. The project will help in relating transient topographic signals to “unconventional” sources in projects studying topography evolution and erosional fluxes in subduction zones, ESR13,15