Coda wave attenuation in the Parecis Basin, Amazon Craton, Brazil: sensitivity to basement depth ... more Coda wave attenuation in the Parecis Basin, Amazon Craton, Brazil: sensitivity to basement depth 1 2 3 Your article is protected by copyright and all rights are held exclusively by Springer Science+Business Media B.V.. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your work, please use the accepted author's version for posting to your own website or your institution's repository. You may further deposit the accepted author's version on a funder's repository at a funder's request, provided it is not made publicly available until 12 months after publication.
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.
Vasile Marza1,∗ , Juraci Carvalho2, Lucas Barros & Cristiano Chimpliganond Seismological Observat... more Vasile Marza1,∗ , Juraci Carvalho2, Lucas Barros & Cristiano Chimpliganond Seismological Observatory, University of Brasilia, Brasilia, DF, Brazil; 1On-leave from Seismological Laborat-ory, National Institute (RD) for Earth Physics, Bucharest, Romania; 2Currently at: ...
Intraplate seismicity has generally poor correlation with surface geological patterns. Except for... more Intraplate seismicity has generally poor correlation with surface geological patterns. Except for major extensional features, such as aborted continental rifts, which may act as weak zones, it is usually difficult to find simple geology based models to explain differences in seismic activity in stable continental regions. Seismicity in Brazil is clearly not uniform and a few areas of higher activity have been identified. However, the seismic areas show almost no correlation with the main geological provinces, which is typical of other intraplate settings. A recent uppermantle tomography study in SE and central Brazil, using approximately 8500 P-wave and 2000 PKP-wave arrivals recorded in 59 sites since 1992, has mapped P-wave velocity anomalies from lithospheric depths down to 1300 km. In this region, higher seismic activity occurs preferentially in areas with low P-wave velocities at 150-250 km depth. The low P-wave velocities are interpreted as shallower asthenosphere. In such areas, a hotter geotherm will reduce the strength of the lithospheric upper mantle causing most of the intraplate forces to be concentrated in the brittle upper crust. The low-velocity anomalies coincide with Late Cretaceous provinces of alkaline intrusions. The proposed ponding of the Trindade plume head beneath lithospheric thin spots is consistent with our tomography results, suggesting that plume effects may have helped to preserve lithosphere/asthenosphere topography. Although other factors are also important, the present data show that stress concentrations resulting from lithosphere/asthenosphere topography should play an important role in explaining the intraplate seismicity in the Brazilian platform.
Resumo Inaugurada em 2006, a Usina Hidrelétrica de Irapé possui a mais alta barragem do país, com... more Resumo Inaugurada em 2006, a Usina Hidrelétrica de Irapé possui a mais alta barragem do país, com 208 metros. Esta vem sendo monitorada pelo Observatório Sismológico da Universidade de Brasília desde o começo do enchimento do seu reservatório. Apresentando sismicidade causada pelo aumento da tensão crustal logo após o início do represamento, a Sismicidade Desencadeada por Reservatório da UHE de Irapé permanece como objeto de estudo importante para o entendimento deste fenômeno. O presente trabalho se propõe a estudar a sismicidade registrada de janeiro a maio de 2006, assim como a caracterizar a geologia ao redor da UHE de Irapé com o intuito de identificar e descrever as estruturas que permitam compreender melhor os eventos sísmicos.
Coda wave attenuation in the Parecis Basin, Amazon Craton, Brazil: sensitivity to basement depth ... more Coda wave attenuation in the Parecis Basin, Amazon Craton, Brazil: sensitivity to basement depth 1 2 3 Your article is protected by copyright and all rights are held exclusively by Springer Science+Business Media B.V.. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your work, please use the accepted author's version for posting to your own website or your institution's repository. You may further deposit the accepted author's version on a funder's repository at a funder's request, provided it is not made publicly available until 12 months after publication.
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.
Vasile Marza1,∗ , Juraci Carvalho2, Lucas Barros & Cristiano Chimpliganond Seismological Observat... more Vasile Marza1,∗ , Juraci Carvalho2, Lucas Barros & Cristiano Chimpliganond Seismological Observatory, University of Brasilia, Brasilia, DF, Brazil; 1On-leave from Seismological Laborat-ory, National Institute (RD) for Earth Physics, Bucharest, Romania; 2Currently at: ...
Intraplate seismicity has generally poor correlation with surface geological patterns. Except for... more Intraplate seismicity has generally poor correlation with surface geological patterns. Except for major extensional features, such as aborted continental rifts, which may act as weak zones, it is usually difficult to find simple geology based models to explain differences in seismic activity in stable continental regions. Seismicity in Brazil is clearly not uniform and a few areas of higher activity have been identified. However, the seismic areas show almost no correlation with the main geological provinces, which is typical of other intraplate settings. A recent uppermantle tomography study in SE and central Brazil, using approximately 8500 P-wave and 2000 PKP-wave arrivals recorded in 59 sites since 1992, has mapped P-wave velocity anomalies from lithospheric depths down to 1300 km. In this region, higher seismic activity occurs preferentially in areas with low P-wave velocities at 150-250 km depth. The low P-wave velocities are interpreted as shallower asthenosphere. In such areas, a hotter geotherm will reduce the strength of the lithospheric upper mantle causing most of the intraplate forces to be concentrated in the brittle upper crust. The low-velocity anomalies coincide with Late Cretaceous provinces of alkaline intrusions. The proposed ponding of the Trindade plume head beneath lithospheric thin spots is consistent with our tomography results, suggesting that plume effects may have helped to preserve lithosphere/asthenosphere topography. Although other factors are also important, the present data show that stress concentrations resulting from lithosphere/asthenosphere topography should play an important role in explaining the intraplate seismicity in the Brazilian platform.
Resumo Inaugurada em 2006, a Usina Hidrelétrica de Irapé possui a mais alta barragem do país, com... more Resumo Inaugurada em 2006, a Usina Hidrelétrica de Irapé possui a mais alta barragem do país, com 208 metros. Esta vem sendo monitorada pelo Observatório Sismológico da Universidade de Brasília desde o começo do enchimento do seu reservatório. Apresentando sismicidade causada pelo aumento da tensão crustal logo após o início do represamento, a Sismicidade Desencadeada por Reservatório da UHE de Irapé permanece como objeto de estudo importante para o entendimento deste fenômeno. O presente trabalho se propõe a estudar a sismicidade registrada de janeiro a maio de 2006, assim como a caracterizar a geologia ao redor da UHE de Irapé com o intuito de identificar e descrever as estruturas que permitam compreender melhor os eventos sísmicos.
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