3D model of the continental forearc (37°S-38.5°S) by inversion of gravimetric data.

In the south-central of Chile, the Nazca plate subducts at an average convergence rate of 66 mm/yr under the South American plate, which is high compared with others subduction zones. This accretionary margin generates large mega-earthquakes, as Mw 9.5 Valdivia 1960, Mw 8.8 Maule 2010. In accretionary margins, it has been observed a correlation between the up-dip limit of seismogenic zone and the backstop, which has led to the supposition that the low friction under the prism of accretion can act as a weak barrier during the propagation of coseismic slip. This suggests a close relation between the upper plate inhomogeneities and seismotectonic of the interplate boundary.

The geology of the zone shows that the continental forearc is composed by coastal platform (marine and minor continental deposits); the Coastal Cordillera, which it is a narrow mountain belt formed by rocks of the Permian-Triassic paired metamorphic belt and late Carboniferous to Permian magmatic arc that forms a prominent batholith known as Nahuelbuta Mountain, result from a major phase of granitoid magmatism; and the Central Valley, it contains Pliocene and Quaternary sediments unconformably overlying late Oligocene to Miocene volcano-sedimentary basin.

This study aims to identify the different structures presents in the area by the modeling onshore gravimetric data to study the relation between the marine and continental structure of the upper plate and find possible relations with the seismotectonics of the margin.

The data base merged gravity stations acquired between 1982 and 2002 by different institutions and complemented with 2019 data acquired by the project CONICYT/FONDECYT 11170047. This new data was registered every two kilometers along the main roads. The initial density model will be generated by several 2D models to estimate the thickness of the young sedimentary coverage and then a 3D inversion will be performed, using UBC-GIF algorithm, to find the different structures of the upper plate.