Can the downdip extent of subducted aseismic ridges under the Andean margin be mapped from published P-wave tomography?

The South American Andean margin is one of the longest active subduction zones in the world and extends about 7500 km from North to South. The Nazca plate was created from the breakup of the Farallon plate 23 million years ago and is currently subducting under western South America. Subduction beneath western South America has been ongoing since possibly the Cretaceous or earlier. Along the Andean margin are orogenic belts and earthquakes of shallow, intermediate and deep (>600 km) depths. Gaps in the Holocene to present volcanic arc along the Peru-Chile trench are linked to the subduction of aseismic ridges (Juan Fernandez ridge, Nazca ridge, and Carnegie ridge) in the Nazca Plate, yet, the downdip orientation, geometry, and extent of these subducted features is ambiguous.

In this study, we attempt to trace subducted features (e.g. aseismic ridges) within the slabs from global P-wave tomography, namely, the models SAM5_P_2019 (Portner et al., 2020), MITP08 (Li et al., 2008), and other models. We create a 3D Nazca mid-slab model using GOCAD software and extract the tomographic velocities along the slab. Our preliminary results show that the slabs downdip of the subducting Carnegie, Juan Fernandez and Nazca ridges exhibit slower velocity anomalies. Our mapped areas near the Juan Fernandez and Nazca ridges appear more reliable based on analysis of published resolution tests. We will compare our mapped mid-slab features to newer adjoint tomography SAAM23 (Ciardelli et al., 2022) and discuss the plate tectonic significance of the mapped features within a quantitative GPlates plate reconstruction.