Unveiling Crustal Heterogeneities in the Central Andes: A High-Resolution Density Model Derived from Integrated Gravity and Seismic Modeling

Understanding the coupled multi-scale geodynamic and tectonic processes related to the subduction of the oceanic Nazca Plate beneath the South American Plate is one pre-requisite to better assess seismic hazards in the region. It is essential to identify all relevant forces and related stress-strain relationships within the subduction system, such as the negative buoyancy of the subducting slab or the degree of mechanical coupling between the Andean domain and the Pampean foreland. We approach this by investigating the present-day physical, in particular rheological state of the lithosphere-asthenosphere system, including first-order variations in pressure, temperature, and rock composition as constrained by multi-disciplinary observations.

This study integrates gravity, active and passive seismic data to construct a high-resolution lithospheric scale density model for the Central Andes, enabling detailed analysis of crustal structural differentiation. For this, a combined workflow of forwardgravity field calculation using IGMAS+ and gravity inversion for the crustal layer using SimPEG is applied. By inverting for crustal densities constrained by both gravity field observations and seismic shear wave velocity conversions for the crust and upper mantle, this work reveals lateral and vertical variations in crustal density that challenge traditional models of upper/lower crustal dichotomy.

With this contribution, we will discuss how the combined information on seismic velocity and gravity-constrained density helps inferring lithological variations within the crust. This is a pre-requisite for investigating variations in the thermal field and mechanical strength of this complex lithosphere-asthenosphere system. In addition, our results provide new insights into the distribution of seismic events in relation to crustal heterogeneity.