Building a 3D gravity-based model of the North Chilean subduction zone constrained by recent seismic results

In the last decade, a large network of permanent seismic stations in Northern Chile (Integrated Plate boundary Observatory Chile network – IPOC) has enabled a range of studies that provided constraints on the geometry of the subduction zone in this region. Larger seismicity compilations and tomography studies have led to a better definition of the downgoing slab, and receiver function studies have illuminated the shape of the continental Moho. This calls for an effort to summarize these diverse constraints in a gravity-based 3D model of the region.

We compiled a 3D integrated geophysical model for Northern Chile in the IGMAS+ software based on the Complete Bouguer Anomaly computed at the Calculation Service of the International Centre for Global Earth Models (ICGEM) from the EIGEN-6C4 Global Gravity Field Model. The 3D gravity-based model represents an update of a similar model by Tassara and Echaurren (2012), which we used as an initial constraint of the geometry and physical properties of our model. The plate interface and slab surface geometry is updated based on the most recent IPOC seismic catalog, and offshore active seismic results. Other significant geophysical interfaces, namely the Moho and the lithosphere-asthenosphere boundary (LAB) in both oceanic and continental domains, were constrained by recently published results from receiver functions, active seismics, seismic tomography, as well as joint inversion and isostatic studies. These studies show considerable uncertainty in the geometry of the mantle wedge near the plate interface. To fit the gravity observations, we had to address the tradeoff between assumed geometry and density distribution, which we did by trying out a range of different shapes and petrophysical properties.

This contribution aims to offer a better understanding of the impact of geometry adjustments, namely in the mantle wedge area, on the gravity response of our 3D model of the North Chilean subduction zone. The final obtained model offers a data-driven 3D geometry that can be used for a wide range of future regional or larger-scale studies.