Morpho-tectonic segmentation vs. seismic segmentation along the Andean margin

Description

In active subduction zones, the sum of the deformation over many seismic cycles accounts for the long-term cumulated deformation of the forearc. Along the Andean coast, several studies have suggested a correlation between the seismic segmentation of the megathrust and the morpho-tectonic segmentation of the forearc. Large megathrust earthquakes tend to occur on highly coupled patches in the seismogenic zone right beneath forearc basins. These basins are often framed in between coastal peninsulas, identified as seismic barriers that impede seismic ruptures propagation. On the contrary, strong coastal uplifts are observed in peninsula areas where the slip along the plate interface is mostly achieved by creeping. These observations suggest a counter-intuitive relationship between megathrust earthquakes, interseismic coupling, and permanent deformations in the upper plate (Saillard et al., 2017). At first order, the permanent deformation recorded in the coastal zone is linked to the seismic behavior on the megathrust whose along-strike variation seems stable through times. We plan to use these observations to resolve the inverse problem: characterization of upper plate Quaternary deformations and active structures distribution would then allow for assessing the margin segmentation, rupture lengths and seismic hazard. Hence the MARACAS program newly funded by the French National Research Agency will address these issues. It proposes to develop an innovative approach to assess seismic hazard in subduction zone that would take into account the survey of the long-term deformation of the upper plate to better identify multicycles margin segmentation. Here, we introduce the MARACAS program scientific question, objectives and potential impacts. Major objectives of the program are 1) to identify the conditions of vertical crustal motions along the plate boundary; 2) to evaluate the lateral impact of seismic ruptures on forearc deformation in weakly coupled segments below peninsulas; and 3) to determine whether the correlation between the seismic segmentation and the morpho-tectonic segmentation is fortuitous or long-lasting.

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