Determinación de la estructura sísmica de la cuenca Pantanal a partir del análisis de velocidad de fase: implementación del primer modo superior de ondas Rayleigh

Abstract

The Pantanal basin is in the upper part of Paraguay river (Mato Grosso do Sul state, Brazil) and there is focus on this basin due to the crustal and lithospheric thinning in this region. Recent works have studied the basin to explain the geodynamic mechanisms of the crust and lithosphere and their relationship with the surrounding areas, estimating that the depth of the LAB (Lithosphere/Asthenosphere Boundary) is shallower than in stable areas of the continent. We propose to analyze the lithospheric structure beneath the Pantanal basin, from 0 to 150 km depth approximately, carrying out an inversion of phase velocity dispersion curves of surface waves, using seismic data from the permanent Brazilian Seismological Network (RSBR). The selected events are of shallow to medium depths, located in the Central Andean region. From these earthquake records, we obtained the dispersion curves for fundamental and first higher modes of Rayleigh waves and fundamental mode of Love waves, applying the Multiple Filter Technique (MFT), combining with a phase match filter to isolate them separately. Then, phase velocity curves, calculated by the two stations method, were inverted to determine vertical profiles for S waves velocities. Furthermore, a sensibility analysis was performed to study the contributions of every component of the surface waves group in the determination of the physical properties by depth. This analysis reveals that the first higher mode can highlight these properties up to the upper mantle. As a result, a representative seismic model of the region was achieved, showing a crust of ~34 km thick and a lithosphere of ~118 km thick. This result suggests a thinner crust and lithosphere than in the surrounding areas.