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Urban seismology has gained scientific interest with the development of seismic ambient noise monitoring techniques and also for being a useful tool to connect society with the Earth sciences. The interpretation of the sources of seismic records generated by sporting events, traffic, or huge agglomerations arouses the population's curiosity and opens up a range of possibilities for new applications of seismology, especially in the area of urban monitoring. In this contribution, we present the analysis of seismic records from a station in the city of Brasilia during unusual episodes of silencing and noisy periods. Usually, cultural noise is observed in high-fequency bands. We showed in our analysis that cultural noise can also be observed in the low-frequency band, when high-frequency signal is attenuated. As examples of noisy periods, we have that of the Soccer World Cup in Brazil in 2014, where changes in noise are related to celebrations of goals and the party held by FIFA in the city, and the political manifestations in the period of the Impeachment trial in 2016, which reached the concentration of about 300,000 protesters. The two most characteristic periods of seismic silence have been the quarantine due to the COVID-19 pandemic in 2020, and the trucker strike that occurred across the country in 2018, both drastically reducing the movement of people in the city. [ABSTRACT FROM AUTHOR]

This work comprises the acquisition, processing and interpretation of 2D seismic shallow refraction (P-wave) and resistivity profiles located in the iron ore deposit of N4WS, Carajás Mineral Province (CMP), northern Brazil. The geophysical methods were used to identify the boundaries of the iron ore deposit. Another objective was to evaluate the potentiality of these geophysical methods in that geological context. In order to validate the results, the geophysical lines were located to match a geological borehole line. For the seismic refraction, we used 120 channels, spaced by 10 m, in a line of 1190 m, with seven shot points. The resistivity method used in the acquisition was the electrical resistivity imaging, with pole-pole array, in order to reach greater depths. The resistivity line had a length of 1430 m, with 10 m spacing between electrodes. The seismic results produced a model with two distinct layers. Based on the velocities values, the first layer was interpreted as altered rocks, and the second layer as more preserved rocks. It was not possible to discriminate different lithologies with the seismic method inside each layer. From the resistivity results, a zone of higher resistivity (> 3937 Ω·m) was interpreted as iron ore, and a region of intermediate resistivity (from 816 to 2330 Ω·m) as altered rocks. These two regions represent the first seismic layer. On the second seismic layer, an area with intermediated resistivity values (from 483 to 2330 Ω·m) was interpreted as mafic rocks, and the area with lower resistivity (< 483 Ω·m) as jaspilite. Our results were compared with geological boreholes and show reasonable correlation, suggesting that the geophysical anomalies correspond to the main variations in composition and physical properties of rocks. [ABSTRACT FROM AUTHOR]

New results of travel time seismic tomography in central Brazil provide evidence that the relatively high seismicity in this region is related to the thinner lithosphere at the limit between the Amazonian and São Francisco paleocontinents. The transition between these paleocontinents is marked by low velocity anomalies, spatially well correlated with the high seismicity region, which are interpreted as related to the lithospheric thinning and consequent rise of the asthenosphere, which have increased the temperature in this region. The low-velocity anomalies suggest a weakness region, favorable to the build-up of stress. The effective elastic thickness and the strain/stress regime for the study area are in agreement with tomographic results. A high-velocity trend is observed beneath the Parnaíba Basin, where low seismicity is observed, indicating the presence of a cratonic core. Our results support the idea that the intraplate seismicity in central Brazil is related to the thin lithosphere underlying parts of the Tocantins Province between the neighboring large cratonic blocks. [ABSTRACT FROM AUTHOR]

We present models for the upper-mantle velocity structure beneath SE and Central Brazil using independent tomographic inversions of P- and S-wave relative arrival-time residuals (including core phases) from teleseismic earthquakes. The events were recorded by a total of 92 stations deployed through different projects, institutions and time periods during the years 1992-2004. Our results show correlations with the main tectonic structures and reveal new anomalies not yet observed in previous works. All interpretations are based on robust anomalies, which appear in the different inversions for P- and S-waves. The resolution is variable through our study volume and has been analyzed through different theoretical test inversions. High-velocity anomalies are observed in the western portion of the São Francisco Craton, supporting the hypothesis that this Craton was part of a major Neoproterozoic plate (San Franciscan Plate). Low-velocity anomalies beneath the Tocantins Province (mainly fold belts between the Amazon and São Francisco Cratons) are interpreted as due to lithospheric thinning, which is consistent with the good correlation between intraplate seismicity and low-velocity anomalies in this region. Our results show that the basement of the Paraná Basin is formed by several blocks, separated by suture zones, according to model of Milani & Ramos. The slab of the Nazca Plate can be observed as a high-velocity anomaly beneath the Paraná Basin, between the depths of 700 and 1200 km. Further, we confirm the low-velocity anomaly in the NE area of the Paraná Basin which has been interpreted by VanDecar et al. as a fossil conduct of the Tristan da Cunha Plume related to the Paraná flood basalt eruptions during the opening of the South Atlantic. [ABSTRACT FROM AUTHOR]

We present a P-wave structure for the sub-continental lithospheric mantle (SCLM) beneath the southern segment of the Amazonian Craton (Central Brazil Shield – CBS) using multiple-frequency tomography. Our model includes 469 seismic events recorded between 2009 and 2017 through 314 seismic stations distributed over South America. From these events, we obtained 20507 P and 12329 PKIKP cross-correlation delays in six frequency bands centered at 0.03, 0.06, 0.13, 0.25, 0.5 and 1 Hz. Despite the limited and heterogeneous resolution throughout the CBS, because of the difficulty in the installation of seismographic stations in areas of dense coverage of tropical forest, our tests show reasonable resolution for lithospheric domains with dimensions greater than 390 × 390 km in most of the study area. We recognized a good correlation between the P-wave anomalies and the tectonic domains defined previously based on geochronology and geological data. The surface projection of these anomalies and their margins are associated with clusters of important Au, Cu–Au and IOCG deposits, as well as diamond-bearing kimberlite intrusions, allowing relating deep structures with shallow features and showing a province-scale control in the distribution of mineral deposits and occurrences in the southern Amazonian craton. • Multiple-frequency seismic tomography in areas with low seismic stations coverage. • Relationship between deep structures and shallow features. • Correlation between P-wave anomalies and mineral deposits in the Amazonian Craton. [ABSTRACT FROM AUTHOR]

In forensic geophysical research, using controlled experiments assists forensic search practitioners in identifying optimal technique(s) and equipment configuration(s) in different burial scenarios. The objective of the research is to observe the geophysical response to different types of buried wrappings, taking into consideration the influence that the presence or absence of a decomposing body (pig carcass) in a lateritic soil in central-western Brazil can have. In this article, the GPR results are presented after a 15day burial period during the rainy season, and the results of Electrical resistivity tomography (ERT) after a burial period of 6 months during the dry season. The controlled site was built in the research area of the University of Brasília, in a region with soil, typical of the Brazilian savannah. 14 simulated clandestine graves of murder victims were constructed, in which seven pig carcasses were wrapped or covered by: soil (backfill), a plastic bag, a bed sheet, cement block, construction debris, a wooden coffin and hydrated lime, respectively a further seven burials, presenting only the wrappings acted as comparison (control burial). During the GPR survey a 400MHz frequency antenna was used. The resistivity surveys were carried out before and after the burial of the targets with dipole-dipole and Wenner-Schlumberger array configurations, with different spacing of electrodes (1.00 and 0.50m). The comparison between the various scenarios with and without pig carcasses revealed that good reflection events occurred mainly due to the wrappings and that pig carcasses attenuated the GPR signal. Electrical resistivity results showed that the Wenner-Schlumberger array presents a better resolution of the lateral boundaries of the burials, and the dipole-dipole array presents a better sensitivity to heterogeneity of the buried materials. The burials with the pig carcasses wrapped in the various materials presented better resistivity contrasts as opposed to the control burials. [ABSTRACT FROM AUTHOR]

Most high-magnitude landslides in Brazil are triggered by rainfall. The partial or total liquefaction of the soil mass is directly related to an increase in the pore pressure, which can happen after or during heavy and sustained rainfalls. Traditional near-surface geophysical methods for saturation and rigidity assessment usually involve short-duration data acquisition campaigns, reporting results representative of a specific moment. On the other hand, the cross-correlation of the ambient noise wavefield registered at different locations in continuous data streams has emerged as a promising alternative for monitoring seismic velocity variations in time. In the present study, we evaluate if the observed seismic velocity perturbations can satisfactorily relate to rainfall periods on a local scale and within minutes of resolution at a slope in Itabirito, state of Minas Gerais, Brazil, where landslide activity occurred. We calculate velocity changes in the tail portion (coda) from Green's functions retrieved from cross-correlation of seismic noise time series registered at pairs of stations from September 2022 to November 2022. In the 50 days observation period, the monitored area remained stable. We identified clear time intervals where the relative seismic velocity decreases after or during rainfall, which indicates modification in the saturation conditions of the soil. The results demonstrated that seismic velocity changes obtained from the coda of cross correlations of the ambient noise wavefield could satisfactorily constrain rainfall periods and indicate possible changes in the saturation conditions of the soil at a small local scale with a high temporal resolution. • A seismic velocity monitoring study is performed at a slope with prior landslide activity. • We identified clear time intervals where the relative seismic velocity decreases after or during rainfall periods. • A depth sensitivity analysis revealed that the velocity changes are likely to occur in the shallow soil layer. • The velocity changes in time relate to rainfall and indicate possible variations in the saturation conditions of the soil. [ABSTRACT FROM AUTHOR]