SeisAndes: A High Resolution Seismic Velocity Model of Crust and Upper Mantle beneath the Central and South Andes from Full Waveform Inversion
Abstract
We present a new combined seismic tomography model based on multi-scale full seismic waveform inversion for the crustal and upper-mantle structure beneath the Central and South Andes, where the oceanic Nazca plate is subducting beneath the South American continent. In order to mitigate the risk of falling into the local minima of optimization, we started our inversions from the lowest frequency signals with lower computational costs. The forward and adjoint simulations on 3D models are accomplished with Salvus (Afanasiev et al., 2018), which is a suite of spectral-element method solver of the seismic wave equation. We conduct the multi-scale inversion tomography using 117 events for Central Andes and 120 events for South Andes, which are carefully selected for better data coverage of the study regions and depth range, taking advantage of the adjoint methodology coupled with L-BFGS with Gaussian smoothing optimisation scheme to update the seismic velocity model. Time-frequency phase shift as misfit functional and adjoint sources is used for long period waveforms and cross-correlation coefficient for short period waveforms. Detailed point-spreading functions are also provided to study the smearing and cross-talking for specific model parameters, demonstrating the robustness of our final model. The subducted fluctuated Nazca slab beneath the Andes is fully imaged, with dip angle variations along the strike from the South Peru to South Chile and Argentina, comprising two flat subductions (Peruvian flat slab and Pampean flat slab) and two normal-dip subductions beneath North and South Chile respectively. Besides, strong low velocity bands in the middle crust and uppermost mantle of the overriding South American plate are also imaged atop of the normal-dip subduction section for North Chile, accompanied by the Holocene volcanic arc, marking the partial melting in the over-thickened crust and hydrated mantle wedge, respectively. Beneath the back-arc for Altiplano and South Puna, we imaged two different lithosphere structure and two different magma chambers beneath the two back-arc volcanic centres, possibly indicating a southward migration history of flat subduction and waning and waxing stages of delamination history for Altiplano and South Puna, respectively.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMS063.0004G
- Keywords:
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- 3225 Numerical approximations and analysis;
- MATHEMATICAL GEOPHYSICS;
- 3260 Inverse theory;
- MATHEMATICAL GEOPHYSICS;
- 7260 Theory;
- SEISMOLOGY;
- 7290 Computational seismology;
- SEISMOLOGY