Geofísica

Apresentam-se os resultados de uma colaboração de mais de trinta anos entre o grupo de Geotermia e Geofísica Nuclear do Instituto de Astronomia, Geofísica e Ciências Atmosféricas da USP e o Laboratório de Análise por Ativação com Nêutrons do IPEN-CNEN/SP, para o estudo de diferentes amostras de rochas extrusivas e intrusivas da Província Magmática do Paraná (PMP), utilizando a Análise por Ativação com Nêutrons como técnica analítica.

We applied a combination of ambient seismic noise and classical earthquake-receiver techniques to characterize the shallow crustal shear-wave velocities in the Quadrilátero Ferrífero (QF), Minas Gerais state, SE Brazil, to a depth of about 4 km. Ambient seismic noise was recorded by up to 26 stations. To improve the signal of the extracted empirical Green's function (EGF), we correlated short time windows of 10 min with 70% overlapping before stacking.

Constraints on the structure of cratonic lithosphere are essential to improve our understanding of craton formation, evolution and long-term stability. Here, we perform a joint inversion for the thermal and compositional structure of the mantle lithosphere below the South America Platform, using Rayleigh wave group velocities, elevation, and geoid height. Thick thermal lithosphere (200–300 km) is found below the southern Amazonian and São Francisco Cratons and adjoining Parecis and eastern Paraná Basins. The southern Rio de la Plata Craton also retains a 200–250 km thick keel.

Magnitude conversions between different scales are important for comparison of seismic activity between different regions, homogenization of earthquake catalogs for seismic hazard calculations, and use of gr

Coeval Neoproterozoic mafic dykes with a well-constrained isotopic age of 925 Ma are distributed in the North China Craton (NCC) of China and São Francisco Craton (SFC) of Brazil. Several recent studies favor the hypothesis that these two cratons were connected during 925 Ma and constituted building cratons for the supercontinent Rodinia. However, the paleo-positions of the two cratons in Rodinia have not yet been paleomagnetically resolved. This paper presents the paleomagnetic results of these dykes in both NCC and SFC.

Groundwater transport in crystalline rocks follows pathways along fractured zones because of low primary porosity and permeability in such formations. Fractured systems encompass an imbricated set of joints and fractures with different lengths, apertures and orientations resulting in complex permeable systems with heterogeneous groundwater transport properties. Geophysical well logging has proved effectiveness in detecting depth levels with denser fracture distributions as well as the apparent aperture of fractures contributing to groundwater flow.

Long-period (T > 10 s) shear wave reflections between the surface and reflecting boundaries below seismic stations are useful for studying phase transitions in the mantle transition zone (MTZ) but shear-velocity heterogeneity and finite-frequency effects complicate the interpretation of waveform stacks. We follow up on a recent study by Shearer & Buehler (hereafter SB19) of the top-side shear wave reflection Ssds as a probe for mapping the depths of the 410-km and 660-km discontinuities beneath the USArray.

The Pitangui Greenstone Belt (PGB) is a Meso to Neoarchean metavolcano-sedimentary sequence, inserted in the Pitangui Synclinorium, located in the northwest portion of the Archean-Paleoproterozoic metallogenic province of the Quadrilátero Ferrífero, southern of the São Francisco 

Soils and groundwater contamination modifies the physical–chemical conditions of the environment, altering natural biogeochemical processes of the ground. As a result, several mineral transformations occur, in which iron plays a decisive role. The presence of iron enables the study of magnetic properties, improving the understanding of the geophysical signatures of highly dynamic environments (e.g., biogeochemical hotspots and contamination plumes).