Effects of the subducting Nazca Plate on South American upper-mantle dynamics, inferred from adjoint waveform tomography

摘要: We use 3D spectral-element seismic wave simulations and data from 112 earthquakes recorded by 1311 seismic stations to construct an adjoint waveform tomography model of South America. We performed 23 iterations using exponentiated instantaneous phase measurements, which optimize the cycle skip problem and the information extracted from each time series. Our final model (SAAM23, South American Adjoint Model-iteration 23) shows a 50% decrease in the misfit relative to its 3D starting model. We assessed SAAM23 by cross-correlation traveltime measurements using 53 earthquakes not included in the adjoint inversion and point-spread function tests. The Nazca Slab is well imaged and is shown to be continuous in the 300-500 km depth range following the Peruvian flat-slab segment. Beneath northern South America, the slab crosses the mantle transition zone and continues into the lower mantle. In …