Reduction of Elastic Thickness at Seaward Chile Trench
Presenter: Zi-Jun Lin                                        Adviser: Jing-Yi Lin

Abstract
The Chilean subduction zone presents a unique opportunity to study trench outer rise deformation of the subducting oceanic lithosphere at different thermal ages. The shape of the outer rise for plate ages ranging from 0 to 50 Ma is predicted by using an elastic plate model with variable elastic thickness Te(x) as a function of the distance measured from the trench axis.
The results show a systematic reduction in Te of up to 50 per cent (or reduction in the flexural rigidity D of up to ∼90 per cent) from the peak of the outer rise to the trench axis. The reduction in Te and D observed in most of the bathymetric profiles is coincident with: (1)strong bending moments (>1016 Nm), (2) reduction in crustal and mantle seismic velocities. The reduction in flexural rigidity towards the trench suggests a weakening of the oceanic lithosphere and is interpreted to be caused partially by fracturing and a likely increase in fluid-pore pressure. In general, our estimates do not show consistent increases in elastic thickness as a function of plate age. This result suggests that either Te is independent of plate age or Te depends strongly on other factors. These factors could include lithospheric weakening due to hydro-fracturing and the loading history of the plate prior to subduction.

References
Contreras-Reyes, E., Grevemeyer, I., Flueh, E.R., Reichert, C., 2008. Upper lithospheric structure of the subduction zone offshore southern Arauco Peninsula, Chile at 38°S. J. Geophys. Res. 113, B07303. doi:10.1029/2007JB005569.

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Contreras-Reyes, E., Osses, A., 2010. Lithospheric flexure modeling seaward of the Chile trench: implications for oceanic plate weakening in the Trench Outer Rise region. Geophys. J. Int. 182 (1), 97–112. doi:10.1111/j.1365-246X.2010.04629.x.

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