Forearc density structure of the overriding plate in the northern area of the giant 1960 Valdivia earthquake

The objective of this work is to analyse the density structure of the continental forearc in the northern segment of the 1960 Mw 9.6 Valdivia earthquake. Regional 2D and local 3D density models have been obtained from available gravity data in the area, complemented by new gravimetric stations. Models are constrained by independent geophysical and geological information and new TEM and MT soundings. The results show a segmentation of the continental wedge along and perpendicular to the margin, high-lighting a high-density anomaly, below the onshore forearc basin, that limits the late Paleozoic-early Mesozoic metamorphic basement in the region where Chaitenia terrane has been proposed. A progressive landward shift of this anomaly correlates with the high slip patch of the giant 1960 M-w 9.6 Valdivia earthquake. Based on these results, we propose that the horizontal extension of the less rigid basement units conforming the marine wedge and Coastal Cordillera domain could modify the process of stress loading during the interseismic periods, and also that changes in position and extension of the late Paleozoic-early Mesozoic accretionary complex could be linked with the frictional properties of the interplate boundary. This analysis provides new evidence of the role of the overriding plate structure in the seismotectonic process in subduction zones.

Automated summary

The objective of this study is to analyze the density structure of the continental forearc in the northern segment of the 1960 Valdivia earthquake. Regional and local density models were obtained using gravity data and were constrained by geophysical and geological information. The results show the segmentation of the continental wedge and a high-density anomaly below the onshore forearc basin. This study suggests that the structure of the overriding plate plays a role in the seismotectonic process in subduction zones.