João Dourado | Universidade Estadual Paulista "Júlio de Mesquita Filho" (original) (raw)
Papers by João Dourado
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...
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Lithosphere
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, ...
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Revista Brasileira de Geofísica
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Revista Brasileira de Geofísica
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...
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Revista Brasileira de Geofísica, 2001
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Revista Brasileira de Geofísica, 2001
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11th International Congress of the Brazilian Geophysical Society & EXPOGEF 2009, Salvador, Bahia, Brazil, 24-28 August 2009, 2009
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Revista Brasileira de Geofísica, 2006
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Revista Brasileira de Geofísica, 2007
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Revista do Instituto Geológico, 2013
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Revista Brasileira de Geofísica, 2001
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Revista Brasileira de Geofísica, 2005
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Intraplate Earthquakes, 2014
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.
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Revista Brasileira de Geofísica, 2006
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Journal of Environmental and Engineering Geophysics, 1999
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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...
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Lithosphere
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, ...
Bookmarks Related papers MentionsView impact
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Revista Brasileira de Geofísica
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Revista Brasileira de Geofísica
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...
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Revista Brasileira de Geofísica, 2001
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Revista Brasileira de Geofísica, 2001
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11th International Congress of the Brazilian Geophysical Society & EXPOGEF 2009, Salvador, Bahia, Brazil, 24-28 August 2009, 2009
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Revista Brasileira de Geofísica, 2006
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Revista Brasileira de Geofísica, 2007
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Revista do Instituto Geológico, 2013
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Revista Brasileira de Geofísica, 2001
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Revista Brasileira de Geofísica, 2005
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Intraplate Earthquakes, 2014
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.
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Revista Brasileira de Geofísica, 2006
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Journal of Environmental and Engineering Geophysics, 1999
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