The continental shelf off SE Brazil is one of the main intraplate seismic zones along the Brazili... more The continental shelf off SE Brazil is one of the main intraplate seismic zones along the Brazilian Atlantic passive margin. Earthquakes with magnitudes larger than 5 mb occur with a return period of 15 to 20 years. Seismic activity occurs mainly along the continental slope suggesting a close relationship with flexural stresses caused by the weight of the sediments. Superposition of regional compressional stresses (from plate boundary forces) with local compression in the upper crust (from flexural bending below the weight of the sediments) explains most of the seismicity pattern. Focal mechanism solutions of previous earthquake in this zone showed reverse faulting on planes dipping roughly 45 degrees, with horizontal P axes. The recent 5.2 mb earthquake of April 23rd, 2008 (125 km south of Sao Vicente), was well recorded by many stations is SE Brazil as well as teleseismic stations in North America, Africa and Antartica. The epicenter is located landwards of the edge of the contine...
Upper mantle seismic anisotropy has been extensively used to infer both present and past deformat... more Upper mantle seismic anisotropy has been extensively used to infer both present and past deformation processes at lithospheric/asthenospheric depths. We present 17 new measurements of the upper mantle fast polarization directions derived from core refracted shear wave splitting (mainly SKS phases) recorded in poorly sampled regions, such as northern and northeastern Brazil. Despite the sparse data coverage of the South American stable platform, consistent orientations are observed over hundreds of kilometers. The fast polarization directions tend to be close to the absolute plate motion given by the hot-spot reference model HS3-NUVEL1A over most of the continent. A previous global comparison of the SKS fast polarization directions with flow models of the upper mantle by Conrad et al.(2007) showed relatively poor correlation in the continents, which was interpreted as evidence for a large contribution of ``frozen'' anisotropy in the lithosphere. For the South American plate, ...
Este trabalho apresenta um uso da geofísica aplicada em uma situação de ambiente urbano. O objeti... more Este trabalho apresenta um uso da geofísica aplicada em uma situação de ambiente urbano. O objetivo dos levantamentos foi o de delimitar a extensão da zona afetada por um colapso e desmoronamento do teto de um túnel em construção sob o Parque do Ibirapuera na capital paulista. São descritos e apresentados os resultados obtidos através do emprego dos métodos geofísicos geoelétricos e suas técnicas, em uma situação emergencial e de risco em uma área urbana na cidade de São Paulo. Também são comparadas as técnicas/arranjos de campo e a forma de apresentação e interpretação dos mesmos. Os métodos empregados foram a Eletrorresistividade, Polarização Induzida (IP) e Potencial Espontâneo (SP). Os trabalhos de campo e interpretação preliminar foram efetuados em apwenas um fim de semana (sábado e domingo). Os resultados mostraram-se plenamente satisfatórios e possibilitaram significativa redução nos custos nas obras de remediação da área do incidente, cuja área decresceu da inicialmente estimada pela engenharia (20x20 m) para 3x5 m definida pelos estudos geofísicos.
This paper presents a case study where geophysics was successfully applied to solve a complex pro... more This paper presents a case study where geophysics was successfully applied to solve a complex problem associated with a tunnel excavation accident in an urban area. It presents and describes the results obtained with geoelectrical methods applied in an emergencial task in a risky urban area in São Paulo City. It also compares the techniques and field arrays, ways to present and interpret the data. The employed methods were electroresistivity, induced polarization (IP) and self potential (SP). The objective of the survey was to delineate the extension of a roof failure of an urban tunnel under excavation beneath the Ibirapuera Park in order to orientate the volume of tunnel roof should be treated. Only two days (Saturday and Sunday) were available to carry out the survey and its interpretation. The results were considered satisfactory and brought a significant economy to the final cost of the tunnel. This economy was due to the decreasing of the remediation area from the initial 20 x...
In order to evaluate the use of shallow seismic technique to delineate geological and geotechnica... more In order to evaluate the use of shallow seismic technique to delineate geological and geotechnical features up to 40 meters depth in noisy urban areas covered with asphalt pavement, five survey lines were conducted in the metropolitan area of São Paulo City. The data were acquired using a 24-bit, 24-channel seismograph, 30 and 100 Hz geophones and a sledgehammer-plate system as seismic source. Seismic reflection data were recorded using a CMP (common mid point) acquisition method. The processing routine consisted of: prestack band-pass filtering (90-250 Hz); automatic gain control (AGC); muting (digital zeroin) of dead/noisy traces, ground roll, air-wave and refractedwave; CMP sorting; velocity analyses; normal move-out corrections; residual static corrections; f-k filtering; CMP stacking. The near surface is geologically characterized by unconsolidated "fill" materials and Quaternary sediments with organic material overlying Tertiary sediments with the water table 2 to 5 m below the surface. The basement is composed of granite and gneiss. Reflections were observed from 40 milliseconds to 65 ms two-way traveltime and were related to the silt clay layer and fine sand layer contact of the Tertiary sediments and to the weathered basement. The CMP seismic-reflection technique has been shown to be useful for mapping the sedimentary layers and the bedrock of the São Paulo sedimentary basin for the purposes of shallow investigations related to engineering problems. In spite of the strong cultural noise observed in these urban areas and problems with planting geophones we verified that, with the proper equipment, field parameters and particularly great care in data collection and processing, we can overcome the adverse field conditions and to image reflections from layers as shallow as 20 meters.
Este trabalho apresenta um uso da geofísica aplicada em uma situação de ambiente urbano. O objeti... more Este trabalho apresenta um uso da geofísica aplicada em uma situação de ambiente urbano. O objetivo dos levantamentos foi o de delimitar a extensão da zona afetada por um colapso e desmoronamento do teto de um túnel em construção sob o Parque do Ibirapuera na capital paulista. São descritos e apresentados os resultados obtidos através do emprego dos métodos geofísicos geoelétricos e suas técnicas, em uma situação emergencial e de risco em uma área urbana na cidade de São Paulo. Também são comparadas as técnicas/arranjos de campo e a forma de apresentação e interpretação dos mesmos. Os métodos empregados foram a Eletrorresistividade, Polarização Induzida (IP) e Potencial Espontâneo (SP). Os trabalhos de campo e interpretação preliminar foram efetuados em apwenas um fim de semana (sábado e domingo). Os resultados mostraram-se plenamente satisfatórios e possibilitaram significativa redução nos custos nas obras de remediação da área do incidente, cuja área decresceu da inicialmente estimada pela engenharia (20x20 m) para 3x5 m definida pelos estudos geofísicos.
The combined use of monitoring wells and geophysical techniques constitutes the form most adequat... more The combined use of monitoring wells and geophysical techniques constitutes the form most adequate for identification and the monitoring contaminated areas. This procedure allows the location of wells and monitoring in strategically points, optimizing the results and minimizing costs. The Electromagnetic Inductive Method (EMI) presents ample possibilities of application in environmental studies due the facility in the acquisition of data, versatility of the equipment in field and the possibility of scanning in the ample areas in short time. This paper realizes a comparative analysis of EMI data collected in 1992 and 2003. The studied place is an industrial area that presents contamination the soil and groundwater for Benzene, Toluene, Xylene, 1,2 dichloroethene, Sodium and Chloride, product of the infiltration of effluent chemistries directly of the ground. The results indicate accented attenuation of the contaminant plume, with probable reduction in the contamination degree.
O Lineamento Guapiara é uma importante feição geológica no Estado de São Paulo, Brasil, associada... more O Lineamento Guapiara é uma importante feição geológica no Estado de São Paulo, Brasil, associada ao vulcanismo mesozoico na Bacia do Paraná. O presente trabalho teve por finalidade a interpretação e modelagem de dados gravimétricos coletados entre as cidades de Capão Bonito e Apiaí (SP), em escala de semi-detalhe, para reconhecimento da geometria da compartimentação crustal ao longo desse lineamento. Os mapas da anomalia Bouguer na área revelam uma notável anomalia gravimétrica positiva de direção NW-SE, que coincide com a orientação da maior concentração de diques associados ao Lineamento Guapiara. O modelo crustal elaborado a partir das anomalias caracteriza um significativo afinamento da crosta na área e corrobora trabalhos anteriores. Esse afinamento seria decorrência da subida do manto, reflexo da atividade epirogenética gerada pela propagação dos esforços tectônicos divergentes que ocorreram na margem da Placa Sul-Americana durante o Cretáceo.
Este trabalho mostra os resultados obtidos com a realização de ensaios geofísicos na em áreas de ... more Este trabalho mostra os resultados obtidos com a realização de ensaios geofísicos na em áreas de lavra de areia, no município de Descalvado, SP. O objetivo dos ensaios é o de detectar cavidades no interior de arenitos, pertencentes às Formações Pirambóia e Botucatu. Estas cavidades formaram-se com o rebaixamento do lençol freático, necessário para as operações de extração da areia. As técnicas geofísicas utilizadas foram: gravimetria, eletrorresistividade (caminhamento elétrico dipolo-dipolo) e radar de penetração no solo (GPR). Na primeira etapa dos trabalhos foram utilizados a gravimetria e a eletrorresistividade em uma bancada onde ocorreu um desmoronamento devido ao abatimento do teto de uma cavidade. Os resultados obtidos com estas duas técnicas foram coerentes pois a gravimetria mostrou baixos gravimétricos indicando uma "ausência de massa" na área de influência da cavidade e o caminhamento detectou um esperado aumento de resistividade elétrica nesta mesma área. Na segunda etapa, com a realização dos ensaios de GPR em uma bancada próxima à anterior, foi possível detectar cavidades por meio das feições hiperbólicas detectadas nos radargramas.
This paper presents an analysis of receiver functions to estimate crustal structure beneath the R... more This paper presents an analysis of receiver functions to estimate crustal structure beneath the Rio Claro Seismological Station, which has been in operation since October 2002. The depths obtained for the Moho discontinuity range from 36 to 44 km. A systematic variation of Moho depths with azimuth was observed. Larger values were obtained with events arriving from the North and the values of 36 km were observed with teleseisms arriving from the SW. This result shows that in the region there is an elevation of the Moho discontinuity near the Domo de Pitanga structural high. This result probably indicates a tectonic origin for this structure caused by deep deformation processes involving the whole lithosphere. RESUMO. Este trabalho apresenta a interpretação da função do receptor determinada para os eventos registrados na Estação Sismológica de Rio Claro, em operação desde outubro de 2002. As profundidades calculadas para a Moho variaram de 36 a 44 km. A análise da variação dos valores de profundidade mostra que eles estão associados aos azimutes dos eventos. Portanto decidiu-se fazer uma análise azimutal dos resultados obtidos. Os maiores valores foram calculados para eventos que se localizamà norte da estação e os valores de 36 km foram calculados para telessismos do quadrante SW. Estes resultados mostram que existe uma elevação da Moho na direção da estrutura "Domo de Pitanga". Estes resultados indicam que esta estruturaé provavelmente de origem tectônica e causada por eventos profundos do manto superior.
In geophysics and seismology, raw data need to be processed to generate useful information that c... more In geophysics and seismology, raw data need to be processed to generate useful information that can be turned into knowledge by researchers. The number of sensors that are acquiring raw data is increasing rapidly. Without good data management systems, more time can be spent in querying and preparing datasets for analyses than in acquiring raw data. Also, a lot of good quality data acquired at great effort can be lost forever if they are not correctly stored. Local and international cooperation will probably be reduced, and a lot of data will never become scientific knowledge. For this reason, the Seismological Laboratory of the Institute of Astronomy, Geophysics and Atmospheric Sciences at the University of São Paulo (IAG-USP) has concentrated fully on its data management system. This report describes the efforts of the IAG-USP to set up a seismology data management system to facilitate local and international cooperation.
ABSTRACT We describe the development of the Brazilian earthquake catalogue and the distribution o... more ABSTRACT We describe the development of the Brazilian earthquake catalogue and the distribution of seismicity in Brazil and neighbouring areas in mid-plate South America. This large mid-plate region is one of the least seismically active stable continental regions (SCR) in the world: the maximum known earthquake had a magnitude of 6.2 mb and events with magnitudes 5 and above occur with a return period of 4 years. Several seismic zones can be delineated in Brazil, including some along craton edges and in sedimentary basins. Overall, the exposed cratonic regions tend to have half as many earthquakes compared to the average expected rate for all of mid-plate South America. Earthquakes tend to occur in Neoproterozoic foldbelts especially in areas of thin lithosphere, or near craton edges around cratonic keels. Areas with positive isostatic gravity anomalies tend to have more earthquakes, indicating that flexural stresses from uncompensated lithospheric loads are an important factor in explaining the intraplate seismicity. We also found that earthquakes are two to three times more likely to occur within 20 km of mapped neotectonic faults, compared to events at larger distances. On closer examination, however, we observe that most of these events occur near but not directly on the major neotectonic faults. This discrepancy could be explained by the model of stress concentration near intersecting structures. The Brazilian passive margin is also a region of higher than average seismicity. Although clear differences are found between different areas along the passive margin (extended crust in southeast Brazil having especially high seismicity compared to thin continental shelves elsewhere), overall the Brazilian passive margin has 70% more earthquakes (magnitudes above 3.5) than the average stable continental region.
Geophysical methods are useful technics of geological investigation, thoroughly employed to diagn... more Geophysical methods are useful technics of geological investigation, thoroughly employed to diagnosis and monitoring contaminated areas, in conjunction with direct techniques of investigation such as chemical analyses. Among these, electric resistivity is more usually used in studies of contaminants in soil and groundwater, due to the high contrast of electric properties between the soil and the pollutant types frequently found, essentially constituted of composed organic and inorganic. Geophysical studies in impacted areas by petroleum products may be describe by anomalies of both low resistivity and high resistivities, confirmed as contaminant by chemical analyses. This apparent contradiction can reflect processes of degradation of the contaminants, directly associated with its residence time in the soil, through the generation of by-products that change the physical properties of the soil and groundwater, principally for the mineral dissolution by action of organic acids and by formation of minerals of oxides and hydroxides minerals. Natural attenuation defines a series of physical, chemical and biological processes that allow the degradation, dispersion and dilution of contaminants in a natural form, in other words, free from human intervention. This paper presents the application of electrical profiling technique in a contaminated industrial area for benzene, toluene, xylene, 1,2 dichloroethene and inorganic salts and it discusses the physical alterations of the contaminated soil through the obtained results, under the optics of the Natural Attenuation in course in the area of study.
The continental shelf off SE Brazil is one of the main intraplate seismic zones along the Brazili... more The continental shelf off SE Brazil is one of the main intraplate seismic zones along the Brazilian Atlantic passive margin. Earthquakes with magnitudes larger than 5 mb occur with a return period of 15 to 20 years. Seismic activity occurs mainly along the continental slope suggesting a close relationship with flexural stresses caused by the weight of the sediments. Superposition of regional compressional stresses (from plate boundary forces) with local compression in the upper crust (from flexural bending below the weight of the sediments) explains most of the seismicity pattern. Focal mechanism solutions of previous earthquake in this zone showed reverse faulting on planes dipping roughly 45 degrees, with horizontal P axes. The recent 5.2 mb earthquake of April 23rd, 2008 (125 km south of Sao Vicente), was well recorded by many stations is SE Brazil as well as teleseismic stations in North America, Africa and Antartica. The epicenter is located landwards of the edge of the contine...
Upper mantle seismic anisotropy has been extensively used to infer both present and past deformat... more Upper mantle seismic anisotropy has been extensively used to infer both present and past deformation processes at lithospheric/asthenospheric depths. We present 17 new measurements of the upper mantle fast polarization directions derived from core refracted shear wave splitting (mainly SKS phases) recorded in poorly sampled regions, such as northern and northeastern Brazil. Despite the sparse data coverage of the South American stable platform, consistent orientations are observed over hundreds of kilometers. The fast polarization directions tend to be close to the absolute plate motion given by the hot-spot reference model HS3-NUVEL1A over most of the continent. A previous global comparison of the SKS fast polarization directions with flow models of the upper mantle by Conrad et al.(2007) showed relatively poor correlation in the continents, which was interpreted as evidence for a large contribution of ``frozen'' anisotropy in the lithosphere. For the South American plate, ...
Este trabalho apresenta um uso da geofísica aplicada em uma situação de ambiente urbano. O objeti... more Este trabalho apresenta um uso da geofísica aplicada em uma situação de ambiente urbano. O objetivo dos levantamentos foi o de delimitar a extensão da zona afetada por um colapso e desmoronamento do teto de um túnel em construção sob o Parque do Ibirapuera na capital paulista. São descritos e apresentados os resultados obtidos através do emprego dos métodos geofísicos geoelétricos e suas técnicas, em uma situação emergencial e de risco em uma área urbana na cidade de São Paulo. Também são comparadas as técnicas/arranjos de campo e a forma de apresentação e interpretação dos mesmos. Os métodos empregados foram a Eletrorresistividade, Polarização Induzida (IP) e Potencial Espontâneo (SP). Os trabalhos de campo e interpretação preliminar foram efetuados em apwenas um fim de semana (sábado e domingo). Os resultados mostraram-se plenamente satisfatórios e possibilitaram significativa redução nos custos nas obras de remediação da área do incidente, cuja área decresceu da inicialmente estimada pela engenharia (20x20 m) para 3x5 m definida pelos estudos geofísicos.
This paper presents a case study where geophysics was successfully applied to solve a complex pro... more This paper presents a case study where geophysics was successfully applied to solve a complex problem associated with a tunnel excavation accident in an urban area. It presents and describes the results obtained with geoelectrical methods applied in an emergencial task in a risky urban area in São Paulo City. It also compares the techniques and field arrays, ways to present and interpret the data. The employed methods were electroresistivity, induced polarization (IP) and self potential (SP). The objective of the survey was to delineate the extension of a roof failure of an urban tunnel under excavation beneath the Ibirapuera Park in order to orientate the volume of tunnel roof should be treated. Only two days (Saturday and Sunday) were available to carry out the survey and its interpretation. The results were considered satisfactory and brought a significant economy to the final cost of the tunnel. This economy was due to the decreasing of the remediation area from the initial 20 x...
In order to evaluate the use of shallow seismic technique to delineate geological and geotechnica... more In order to evaluate the use of shallow seismic technique to delineate geological and geotechnical features up to 40 meters depth in noisy urban areas covered with asphalt pavement, five survey lines were conducted in the metropolitan area of São Paulo City. The data were acquired using a 24-bit, 24-channel seismograph, 30 and 100 Hz geophones and a sledgehammer-plate system as seismic source. Seismic reflection data were recorded using a CMP (common mid point) acquisition method. The processing routine consisted of: prestack band-pass filtering (90-250 Hz); automatic gain control (AGC); muting (digital zeroin) of dead/noisy traces, ground roll, air-wave and refractedwave; CMP sorting; velocity analyses; normal move-out corrections; residual static corrections; f-k filtering; CMP stacking. The near surface is geologically characterized by unconsolidated "fill" materials and Quaternary sediments with organic material overlying Tertiary sediments with the water table 2 to 5 m below the surface. The basement is composed of granite and gneiss. Reflections were observed from 40 milliseconds to 65 ms two-way traveltime and were related to the silt clay layer and fine sand layer contact of the Tertiary sediments and to the weathered basement. The CMP seismic-reflection technique has been shown to be useful for mapping the sedimentary layers and the bedrock of the São Paulo sedimentary basin for the purposes of shallow investigations related to engineering problems. In spite of the strong cultural noise observed in these urban areas and problems with planting geophones we verified that, with the proper equipment, field parameters and particularly great care in data collection and processing, we can overcome the adverse field conditions and to image reflections from layers as shallow as 20 meters.
Este trabalho apresenta um uso da geofísica aplicada em uma situação de ambiente urbano. O objeti... more Este trabalho apresenta um uso da geofísica aplicada em uma situação de ambiente urbano. O objetivo dos levantamentos foi o de delimitar a extensão da zona afetada por um colapso e desmoronamento do teto de um túnel em construção sob o Parque do Ibirapuera na capital paulista. São descritos e apresentados os resultados obtidos através do emprego dos métodos geofísicos geoelétricos e suas técnicas, em uma situação emergencial e de risco em uma área urbana na cidade de São Paulo. Também são comparadas as técnicas/arranjos de campo e a forma de apresentação e interpretação dos mesmos. Os métodos empregados foram a Eletrorresistividade, Polarização Induzida (IP) e Potencial Espontâneo (SP). Os trabalhos de campo e interpretação preliminar foram efetuados em apwenas um fim de semana (sábado e domingo). Os resultados mostraram-se plenamente satisfatórios e possibilitaram significativa redução nos custos nas obras de remediação da área do incidente, cuja área decresceu da inicialmente estimada pela engenharia (20x20 m) para 3x5 m definida pelos estudos geofísicos.
The combined use of monitoring wells and geophysical techniques constitutes the form most adequat... more The combined use of monitoring wells and geophysical techniques constitutes the form most adequate for identification and the monitoring contaminated areas. This procedure allows the location of wells and monitoring in strategically points, optimizing the results and minimizing costs. The Electromagnetic Inductive Method (EMI) presents ample possibilities of application in environmental studies due the facility in the acquisition of data, versatility of the equipment in field and the possibility of scanning in the ample areas in short time. This paper realizes a comparative analysis of EMI data collected in 1992 and 2003. The studied place is an industrial area that presents contamination the soil and groundwater for Benzene, Toluene, Xylene, 1,2 dichloroethene, Sodium and Chloride, product of the infiltration of effluent chemistries directly of the ground. The results indicate accented attenuation of the contaminant plume, with probable reduction in the contamination degree.
O Lineamento Guapiara é uma importante feição geológica no Estado de São Paulo, Brasil, associada... more O Lineamento Guapiara é uma importante feição geológica no Estado de São Paulo, Brasil, associada ao vulcanismo mesozoico na Bacia do Paraná. O presente trabalho teve por finalidade a interpretação e modelagem de dados gravimétricos coletados entre as cidades de Capão Bonito e Apiaí (SP), em escala de semi-detalhe, para reconhecimento da geometria da compartimentação crustal ao longo desse lineamento. Os mapas da anomalia Bouguer na área revelam uma notável anomalia gravimétrica positiva de direção NW-SE, que coincide com a orientação da maior concentração de diques associados ao Lineamento Guapiara. O modelo crustal elaborado a partir das anomalias caracteriza um significativo afinamento da crosta na área e corrobora trabalhos anteriores. Esse afinamento seria decorrência da subida do manto, reflexo da atividade epirogenética gerada pela propagação dos esforços tectônicos divergentes que ocorreram na margem da Placa Sul-Americana durante o Cretáceo.
Este trabalho mostra os resultados obtidos com a realização de ensaios geofísicos na em áreas de ... more Este trabalho mostra os resultados obtidos com a realização de ensaios geofísicos na em áreas de lavra de areia, no município de Descalvado, SP. O objetivo dos ensaios é o de detectar cavidades no interior de arenitos, pertencentes às Formações Pirambóia e Botucatu. Estas cavidades formaram-se com o rebaixamento do lençol freático, necessário para as operações de extração da areia. As técnicas geofísicas utilizadas foram: gravimetria, eletrorresistividade (caminhamento elétrico dipolo-dipolo) e radar de penetração no solo (GPR). Na primeira etapa dos trabalhos foram utilizados a gravimetria e a eletrorresistividade em uma bancada onde ocorreu um desmoronamento devido ao abatimento do teto de uma cavidade. Os resultados obtidos com estas duas técnicas foram coerentes pois a gravimetria mostrou baixos gravimétricos indicando uma "ausência de massa" na área de influência da cavidade e o caminhamento detectou um esperado aumento de resistividade elétrica nesta mesma área. Na segunda etapa, com a realização dos ensaios de GPR em uma bancada próxima à anterior, foi possível detectar cavidades por meio das feições hiperbólicas detectadas nos radargramas.
This paper presents an analysis of receiver functions to estimate crustal structure beneath the R... more This paper presents an analysis of receiver functions to estimate crustal structure beneath the Rio Claro Seismological Station, which has been in operation since October 2002. The depths obtained for the Moho discontinuity range from 36 to 44 km. A systematic variation of Moho depths with azimuth was observed. Larger values were obtained with events arriving from the North and the values of 36 km were observed with teleseisms arriving from the SW. This result shows that in the region there is an elevation of the Moho discontinuity near the Domo de Pitanga structural high. This result probably indicates a tectonic origin for this structure caused by deep deformation processes involving the whole lithosphere. RESUMO. Este trabalho apresenta a interpretação da função do receptor determinada para os eventos registrados na Estação Sismológica de Rio Claro, em operação desde outubro de 2002. As profundidades calculadas para a Moho variaram de 36 a 44 km. A análise da variação dos valores de profundidade mostra que eles estão associados aos azimutes dos eventos. Portanto decidiu-se fazer uma análise azimutal dos resultados obtidos. Os maiores valores foram calculados para eventos que se localizamà norte da estação e os valores de 36 km foram calculados para telessismos do quadrante SW. Estes resultados mostram que existe uma elevação da Moho na direção da estrutura "Domo de Pitanga". Estes resultados indicam que esta estruturaé provavelmente de origem tectônica e causada por eventos profundos do manto superior.
In geophysics and seismology, raw data need to be processed to generate useful information that c... more In geophysics and seismology, raw data need to be processed to generate useful information that can be turned into knowledge by researchers. The number of sensors that are acquiring raw data is increasing rapidly. Without good data management systems, more time can be spent in querying and preparing datasets for analyses than in acquiring raw data. Also, a lot of good quality data acquired at great effort can be lost forever if they are not correctly stored. Local and international cooperation will probably be reduced, and a lot of data will never become scientific knowledge. For this reason, the Seismological Laboratory of the Institute of Astronomy, Geophysics and Atmospheric Sciences at the University of São Paulo (IAG-USP) has concentrated fully on its data management system. This report describes the efforts of the IAG-USP to set up a seismology data management system to facilitate local and international cooperation.
ABSTRACT We describe the development of the Brazilian earthquake catalogue and the distribution o... more ABSTRACT We describe the development of the Brazilian earthquake catalogue and the distribution of seismicity in Brazil and neighbouring areas in mid-plate South America. This large mid-plate region is one of the least seismically active stable continental regions (SCR) in the world: the maximum known earthquake had a magnitude of 6.2 mb and events with magnitudes 5 and above occur with a return period of 4 years. Several seismic zones can be delineated in Brazil, including some along craton edges and in sedimentary basins. Overall, the exposed cratonic regions tend to have half as many earthquakes compared to the average expected rate for all of mid-plate South America. Earthquakes tend to occur in Neoproterozoic foldbelts especially in areas of thin lithosphere, or near craton edges around cratonic keels. Areas with positive isostatic gravity anomalies tend to have more earthquakes, indicating that flexural stresses from uncompensated lithospheric loads are an important factor in explaining the intraplate seismicity. We also found that earthquakes are two to three times more likely to occur within 20 km of mapped neotectonic faults, compared to events at larger distances. On closer examination, however, we observe that most of these events occur near but not directly on the major neotectonic faults. This discrepancy could be explained by the model of stress concentration near intersecting structures. The Brazilian passive margin is also a region of higher than average seismicity. Although clear differences are found between different areas along the passive margin (extended crust in southeast Brazil having especially high seismicity compared to thin continental shelves elsewhere), overall the Brazilian passive margin has 70% more earthquakes (magnitudes above 3.5) than the average stable continental region.
Geophysical methods are useful technics of geological investigation, thoroughly employed to diagn... more Geophysical methods are useful technics of geological investigation, thoroughly employed to diagnosis and monitoring contaminated areas, in conjunction with direct techniques of investigation such as chemical analyses. Among these, electric resistivity is more usually used in studies of contaminants in soil and groundwater, due to the high contrast of electric properties between the soil and the pollutant types frequently found, essentially constituted of composed organic and inorganic. Geophysical studies in impacted areas by petroleum products may be describe by anomalies of both low resistivity and high resistivities, confirmed as contaminant by chemical analyses. This apparent contradiction can reflect processes of degradation of the contaminants, directly associated with its residence time in the soil, through the generation of by-products that change the physical properties of the soil and groundwater, principally for the mineral dissolution by action of organic acids and by formation of minerals of oxides and hydroxides minerals. Natural attenuation defines a series of physical, chemical and biological processes that allow the degradation, dispersion and dilution of contaminants in a natural form, in other words, free from human intervention. This paper presents the application of electrical profiling technique in a contaminated industrial area for benzene, toluene, xylene, 1,2 dichloroethene and inorganic salts and it discusses the physical alterations of the contaminated soil through the obtained results, under the optics of the Natural Attenuation in course in the area of study.
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Papers by João Dourado