Periodic coastal uplift in a subduction context

Topography in subduction zones is commonly seen as the consequence of tectonic processes occurring at the plate interface where mega-earthquakes such as the one in Sumatra (2004) or Tohoku (Japan, 2011) occur. A good understanding of the relationship between these deep-seated processes and the topographic response at the surface is therefore crucial, particularly given the potentially densely populated coastal areas bordering these subduction zones (e.g. Japan, Latin America).

Using advanced numerical modelling techniques, this study shows that the accretion of fragments of oceanic crust at the base of the upper plate is responsible for vertical oscillations at the surface of several hundred metres with a periodicity of a few million years (as if the surface above the subductions were ‘breathing’ slowly and regularly). This ‘long-term’ signal is virtually undetectable by the methods commonly used to measure these vertical movements (e.g. GPS, study of marine terraces) and is superimposed on the ‘short-term’ vertical movements triggered during the seismic cycle.

These results therefore show the importance of studying topographic variations along active margins in order to identify these accretion episodes and constrain frictional properties along the subduction plane.