Juraci Carvalho | Universidade de Brasília - UnB (original) (raw)
Papers by Juraci Carvalho
Proceeding of the 17th International Congress of the Brazilian Geophysical, 2021
Contents of this paper were reviewed by the Technical Committee of the 17 th International Congre... more Contents of this paper were reviewed by the Technical Committee of the 17 th International Congress of the Brazilian Geophysical Society and do not necessarily represent any position of the SBGf, its officers or members. Electronic reproduction or storage of any part of this paper for commercial purposes without the written consent of the Brazilian Geophysical Society is prohibited.
AGU Fall Meeting Abstracts, Dec 1, 2018
Brazilian Journal of Geophysics
Brazilian Journal of Geophysics
ABSTRACT. The Beirut, Lebanon, explosion on August 4, 2020, one of the largest non-nuclear explos... more ABSTRACT. The Beirut, Lebanon, explosion on August 4, 2020, one of the largest non-nuclear explosion in world history, was detected by infrasound and seismic stations of the International Monitoring System (IMS), a network designed to detect and locate nuclear explosions in violation to the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The explosion was registered by five infrasound and three seismic stations, located up to 6,000 km and 2,400 km distant, respectively. These IMS data, complemented by data from seven ocean bottom stations, were used to estimate epicenter, magnitudes (mb = 3.6 and Mw = 3.3) and explosive yield. The explosion location was determined by infrasound (33,864ºN and 34,311ºE) and seismic (33,859ºN and 35,567ºE) technologies. The yield was calculated using two approaches: the seismic P-wave magnitude and the maximum amplitude of the infrasonic signal, resulting in 0.40 kt and 1.48 kt of trinitrotoluene (TNT) equivalent, respectively. The aim of this work is te...
13th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 26–29 August 2013, 2013
Proceedings of the 16th International Congress of the Brazilian Geophysical Society&Expogef, 2019
The biggest earthquake ever observed in all Stable Continental Interior (SCI) of the South Americ... more The biggest earthquake ever observed in all Stable Continental Interior (SCI) of the South American plate occurred in Serra do Tombador (ST), Mato Grosso State, in 1955. 100km to northeast of ST, in Porto dos Gaúchos (PG), a recurrent seismicity has been observed since 1959 and earthquakes continues to be detected in this area up today. Two magnitudes 5 earthquakes occurred in 1998 and 2005 with intensities up to VI and V, respectively. Recently, on January 26 of 2015 it was detected, 17km away from the PG seismic zone, another seismic activity with a main shock of magnitude 4.0mb. This new seismic area, is parallel to PG fault, with similar Focal Mechanism to the 1998 and 2005 seismic sequences. The seismicity in these three seismic areas did not present any relation with geological structures presents in this region. However, in light of new studies on Intraplate seismicity, it seems that these seismicities are interconnected: Serra do Tombador earthquake of 1955 Triggered Porto dos Gaúchos (PG) earthquakes and PG earthquakes Triggered the seismicity that has being observed in the new seismic zone since January 2015. This work aims to present results of studies that has been made about this new seismic zone, but before that, we will do a revision on the studies made about the seismicity in ST and PG seismic zones.
Journal of South American Earth Sciences, 2015
Focal-mechanism determination of weak events recorded in sparse networks is challenging. First-mo... more Focal-mechanism determination of weak events recorded in sparse networks is challenging. First-motion polarities are often available at relatively distant stations, and waveforms only at a few near stations can be modeled. A two-step approach of how to combine such data has been suggested recently (Cyclic Scanning of the Polarity Solutions, or CSPS method; Fojtíkov a and Zahradník, 2014). It starts with creating a suite of first-motion polarity solutions, which is often highly non-unique. The next step consists of repeating full waveform inversion for all polarity solutions. Even few stations may efficiently reduce the non-uniqueness of the polarity solutions. Centroid depth, time, scalar moment and uncertainty estimate of the well-fitting double-couple solutions are obtained. The CSPS method has been extended in this paper by adding a new feature, i.e. repeated inversions using multiple first-motion polarity sets. The polarity sets are created by projecting the stations on focal sphere in several available velocity models, thus accounting for the takeoff angle uncertainty. The multiple polarity sets provide assessment of the CSPS solution stability. These ideas are demonstrated on a comprehensive analysis of a rare event in central Brazil. It is the Mw~4 mainshock of the Mara Rosa 2010 earthquake sequence (Barros et al., 2015, Carvalho et al., 2015). We employ polarities at 11 stations (distances < 730 km) and invert full waveforms at two stations (CAN3 and BDFB at distances~120 and 240 km), for 0.1e0.2 and 0.05e0.125 Hz, respectively. Six polarity sets reflect the takeoff angle uncertainty. The obtained CSPS results are very stable across all the polarity sets (in terms of depth, Mw, and strike/dip/rake angles). It is found that the Mara Rosa mainshock mechanism deviated from the composite solution of the whole sequence by 38. The paper also includes a test simulating situations at which just a single waveform is used, and how it negatively affects the solution stability.
On October 8th, 2010, a 5.0 mb earthquake with intensity VI (MM) occurred close to Mara Rosa, in ... more On October 8th, 2010, a 5.0 mb earthquake with intensity VI (MM) occurred close to Mara Rosa, in the North of Goias State, central Brazil, in an area where previous low magnitude seismicity had been observed. This earthquake was felt up to 300 km away from the epicenter, and was the biggest event ever detected in Central Brazil Seismic Zone. Despite the difficulty of associating earthquakes in Stable Continental Interior with geological structures, this event is possibly related to the reactivation of a geological fault of the continental-scale Transbrasiliano Lineament (TBL): the aftershock activity observed with an 8-station seismic network, indicates a NW dipping, SW-NE trending reverse fault, parallel to the TBL. The P axis is NW-SE oriented, consistent with expected stress direction in the region. Cross correlation technique was used to synchronize the weak P- and S- wave phases of some of the aftershocks, recorded at regional stations, with the corresponding arrivals of the ma...
In this paper we present the results of the Focal Mechanisms (FM) determination for four weak eve... more In this paper we present the results of the Focal Mechanisms (FM) determination for four weak events from the Goiás-Tocantins Seismic Zone (GTSZ) using the method of Cyclic Scanning of the Polarity Solutions (CSPS), such method makes use of the full waveform inversion to constrain the non-unique focal mechanism solutions, obtained by the FOCMEC program, from a set of few available polarities only. The solution reliability is controlled by a series of quality control parameters. The events occurred in the Brazil Central region, close to the cities of Mara Rosa/GO (2010), Formoso/GO (2011), Aliança/TO (2011) and Peixe/TO (2015).
<p>Mitigating intraplate earthquakes is necessary, as local populations are at risk... more <p>Mitigating intraplate earthquakes is necessary, as local populations are at risk both directly from strong shaking and indirectly from the threat to public infrastructure such as dams. However, the infrequency of these events and insufficient knowledge of how the ground will respond to passing seismic waves challenges mitigation. In Brazil, one M 5 earthquake occurs about every 5 years. M 4 earthquakes are more common and produce shaking intensities up to VI and VII on the Modified Mercalli scale. Brazilian earthquakes are shallower on average than events in other intraplate regions, which raises the possibility that fault mechanics and earthquake dynamics are different here. To work toward improving hazard mitigation and to better understand the physics of earthquakes in Brazil, we present 3D numerical models of the rupture process of two recent earthquakes using the open-source dynamic rupture and wave propagation software, SeisSol (www.seissol.org). Typically, sparse data prohibits the modeling of intraplate events. However, the 2010 Mara Rosa earthquake, the largest earthquake ever recorded in the Goi&#225;s-Tocantins Seismic Zone in central Brazil, and the 2017 Maranh&#227;o earthquake, which occurred in a previously aseismic region of northern Brazil, are relatively well studied and ample data is available. We report results within the range of uncertainty from the uncertainty in observations of stress drop, epicentral depth, fault geometry and regional stress state. The Mara Rosa earthquake occurred at an epicentral depth of ~2 km, while the Maranh&#227;o earthquake occurred between ~12-16 km depth. Modeling these two events allows us to contrast the influence of depth on the modeled earthquake source characteristics. We propose that fault cohesion dominates fault strength for the shallowest intraplate events, assuming a typical Mohr-Coulomb relationship.</p>
Proceedings of the VIII Simpósio Brasileiro e Geofísica, 2018
Here it is presented the preliminary results of study, with local network, of the aftershock acti... more Here it is presented the preliminary results of study, with local network, of the aftershock activity occurred in the aseismic region of Vargem Grande, Maranhão state, after a 4.6 mb mainshock on January 3, 2017. The focal mechanism solution indicates a strike slip fault with compression parallel to the cost line in agreement with previous studies. The aftershock activity was very intense in the begin fading to just few events after couple of days and the aftershock network only registered 60 events within two months. Hypocentral location of 10 events showed a possible trace of the fault in agreement with focal mechanism solution. The relocation of the main event with station correction and fixed depth was located within the aftershock cluster with accuracy of a GT5 event requirements.
7th International Congress of the Brazilian Geophysical Society
Proceedings of the 7 Simpósio Brasileiro de Geofísica
The present study introduces the first steps of a Support Vector Machine (SVM) algorithm using tw... more The present study introduces the first steps of a Support Vector Machine (SVM) algorithm using two discrimination features: spectral ratio and waveform complexity on a dataset characterized by lower magnitude events recorded by a local network in Minas Gerais State, Brazil. The selected data set consists of 43 microearthquakes and 39 mining blasts of similar magnitudes and locations. The analysis was carried out using data of vertical short period components of two 3C seismic stations. Our results revealed that despite of some overlapping, these techniques show a good capacity to discriminate artificial by natural events for the studied region. However, for short distances (~3 km), the technique deserves more attention.
Proceedings of the 6 Simpósio Brasileiro de Geofísica
Este trabalho apresentou os resultados das análises dos dados recentes da rede sísmica de Montes ... more Este trabalho apresentou os resultados das análises dos dados recentes da rede sísmica de Montes Claros. Observou-se que nos primeiros meses de 2014 (até 11 de abril) houve uma reativação da sismicidade com uma migração dos epicentros para o noroeste, se afastando da cidade. Isto indica uma maior extensão da falha sismogênica. A inversão de formas de ondas em duas estações da rede indica que os regimes de esforços para sismicidade atual e aquela observada até junho de 2013 são semelhantes.
Proceedings of the 7 Simpósio Brasileiro de Geofísica
In this paper we present the results of the Focal Mechanisms (FM) determination for four weak eve... more In this paper we present the results of the Focal Mechanisms (FM) determination for four weak events from the Goiás-Tocantins Seismic Zone (GTSZ) using the method of Cyclic Scanning of the Polarity Solutions (CSPS), such method makes use of the full waveform inversion to constrain the non-unique focal mechanism solutions, obtained by the FOCMEC program, from a set of few available polarities only. The solution reliability is controlled by a series of quality control parameters. The events occurred in the Brazil Central region, close to the cities of Mara Rosa/GO
Proceeding of the 17th International Congress of the Brazilian Geophysical, 2021
Contents of this paper were reviewed by the Technical Committee of the 17 th International Congre... more Contents of this paper were reviewed by the Technical Committee of the 17 th International Congress of the Brazilian Geophysical Society and do not necessarily represent any position of the SBGf, its officers or members. Electronic reproduction or storage of any part of this paper for commercial purposes without the written consent of the Brazilian Geophysical Society is prohibited.
AGU Fall Meeting Abstracts, Dec 1, 2018
Brazilian Journal of Geophysics
Brazilian Journal of Geophysics
ABSTRACT. The Beirut, Lebanon, explosion on August 4, 2020, one of the largest non-nuclear explos... more ABSTRACT. The Beirut, Lebanon, explosion on August 4, 2020, one of the largest non-nuclear explosion in world history, was detected by infrasound and seismic stations of the International Monitoring System (IMS), a network designed to detect and locate nuclear explosions in violation to the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The explosion was registered by five infrasound and three seismic stations, located up to 6,000 km and 2,400 km distant, respectively. These IMS data, complemented by data from seven ocean bottom stations, were used to estimate epicenter, magnitudes (mb = 3.6 and Mw = 3.3) and explosive yield. The explosion location was determined by infrasound (33,864ºN and 34,311ºE) and seismic (33,859ºN and 35,567ºE) technologies. The yield was calculated using two approaches: the seismic P-wave magnitude and the maximum amplitude of the infrasonic signal, resulting in 0.40 kt and 1.48 kt of trinitrotoluene (TNT) equivalent, respectively. The aim of this work is te...
13th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 26–29 August 2013, 2013
Proceedings of the 16th International Congress of the Brazilian Geophysical Society&Expogef, 2019
The biggest earthquake ever observed in all Stable Continental Interior (SCI) of the South Americ... more The biggest earthquake ever observed in all Stable Continental Interior (SCI) of the South American plate occurred in Serra do Tombador (ST), Mato Grosso State, in 1955. 100km to northeast of ST, in Porto dos Gaúchos (PG), a recurrent seismicity has been observed since 1959 and earthquakes continues to be detected in this area up today. Two magnitudes 5 earthquakes occurred in 1998 and 2005 with intensities up to VI and V, respectively. Recently, on January 26 of 2015 it was detected, 17km away from the PG seismic zone, another seismic activity with a main shock of magnitude 4.0mb. This new seismic area, is parallel to PG fault, with similar Focal Mechanism to the 1998 and 2005 seismic sequences. The seismicity in these three seismic areas did not present any relation with geological structures presents in this region. However, in light of new studies on Intraplate seismicity, it seems that these seismicities are interconnected: Serra do Tombador earthquake of 1955 Triggered Porto dos Gaúchos (PG) earthquakes and PG earthquakes Triggered the seismicity that has being observed in the new seismic zone since January 2015. This work aims to present results of studies that has been made about this new seismic zone, but before that, we will do a revision on the studies made about the seismicity in ST and PG seismic zones.
Journal of South American Earth Sciences, 2015
Focal-mechanism determination of weak events recorded in sparse networks is challenging. First-mo... more Focal-mechanism determination of weak events recorded in sparse networks is challenging. First-motion polarities are often available at relatively distant stations, and waveforms only at a few near stations can be modeled. A two-step approach of how to combine such data has been suggested recently (Cyclic Scanning of the Polarity Solutions, or CSPS method; Fojtíkov a and Zahradník, 2014). It starts with creating a suite of first-motion polarity solutions, which is often highly non-unique. The next step consists of repeating full waveform inversion for all polarity solutions. Even few stations may efficiently reduce the non-uniqueness of the polarity solutions. Centroid depth, time, scalar moment and uncertainty estimate of the well-fitting double-couple solutions are obtained. The CSPS method has been extended in this paper by adding a new feature, i.e. repeated inversions using multiple first-motion polarity sets. The polarity sets are created by projecting the stations on focal sphere in several available velocity models, thus accounting for the takeoff angle uncertainty. The multiple polarity sets provide assessment of the CSPS solution stability. These ideas are demonstrated on a comprehensive analysis of a rare event in central Brazil. It is the Mw~4 mainshock of the Mara Rosa 2010 earthquake sequence (Barros et al., 2015, Carvalho et al., 2015). We employ polarities at 11 stations (distances < 730 km) and invert full waveforms at two stations (CAN3 and BDFB at distances~120 and 240 km), for 0.1e0.2 and 0.05e0.125 Hz, respectively. Six polarity sets reflect the takeoff angle uncertainty. The obtained CSPS results are very stable across all the polarity sets (in terms of depth, Mw, and strike/dip/rake angles). It is found that the Mara Rosa mainshock mechanism deviated from the composite solution of the whole sequence by 38. The paper also includes a test simulating situations at which just a single waveform is used, and how it negatively affects the solution stability.
On October 8th, 2010, a 5.0 mb earthquake with intensity VI (MM) occurred close to Mara Rosa, in ... more On October 8th, 2010, a 5.0 mb earthquake with intensity VI (MM) occurred close to Mara Rosa, in the North of Goias State, central Brazil, in an area where previous low magnitude seismicity had been observed. This earthquake was felt up to 300 km away from the epicenter, and was the biggest event ever detected in Central Brazil Seismic Zone. Despite the difficulty of associating earthquakes in Stable Continental Interior with geological structures, this event is possibly related to the reactivation of a geological fault of the continental-scale Transbrasiliano Lineament (TBL): the aftershock activity observed with an 8-station seismic network, indicates a NW dipping, SW-NE trending reverse fault, parallel to the TBL. The P axis is NW-SE oriented, consistent with expected stress direction in the region. Cross correlation technique was used to synchronize the weak P- and S- wave phases of some of the aftershocks, recorded at regional stations, with the corresponding arrivals of the ma...
In this paper we present the results of the Focal Mechanisms (FM) determination for four weak eve... more In this paper we present the results of the Focal Mechanisms (FM) determination for four weak events from the Goiás-Tocantins Seismic Zone (GTSZ) using the method of Cyclic Scanning of the Polarity Solutions (CSPS), such method makes use of the full waveform inversion to constrain the non-unique focal mechanism solutions, obtained by the FOCMEC program, from a set of few available polarities only. The solution reliability is controlled by a series of quality control parameters. The events occurred in the Brazil Central region, close to the cities of Mara Rosa/GO (2010), Formoso/GO (2011), Aliança/TO (2011) and Peixe/TO (2015).
<p>Mitigating intraplate earthquakes is necessary, as local populations are at risk... more <p>Mitigating intraplate earthquakes is necessary, as local populations are at risk both directly from strong shaking and indirectly from the threat to public infrastructure such as dams. However, the infrequency of these events and insufficient knowledge of how the ground will respond to passing seismic waves challenges mitigation. In Brazil, one M 5 earthquake occurs about every 5 years. M 4 earthquakes are more common and produce shaking intensities up to VI and VII on the Modified Mercalli scale. Brazilian earthquakes are shallower on average than events in other intraplate regions, which raises the possibility that fault mechanics and earthquake dynamics are different here. To work toward improving hazard mitigation and to better understand the physics of earthquakes in Brazil, we present 3D numerical models of the rupture process of two recent earthquakes using the open-source dynamic rupture and wave propagation software, SeisSol (www.seissol.org). Typically, sparse data prohibits the modeling of intraplate events. However, the 2010 Mara Rosa earthquake, the largest earthquake ever recorded in the Goi&#225;s-Tocantins Seismic Zone in central Brazil, and the 2017 Maranh&#227;o earthquake, which occurred in a previously aseismic region of northern Brazil, are relatively well studied and ample data is available. We report results within the range of uncertainty from the uncertainty in observations of stress drop, epicentral depth, fault geometry and regional stress state. The Mara Rosa earthquake occurred at an epicentral depth of ~2 km, while the Maranh&#227;o earthquake occurred between ~12-16 km depth. Modeling these two events allows us to contrast the influence of depth on the modeled earthquake source characteristics. We propose that fault cohesion dominates fault strength for the shallowest intraplate events, assuming a typical Mohr-Coulomb relationship.</p>
Proceedings of the VIII Simpósio Brasileiro e Geofísica, 2018
Here it is presented the preliminary results of study, with local network, of the aftershock acti... more Here it is presented the preliminary results of study, with local network, of the aftershock activity occurred in the aseismic region of Vargem Grande, Maranhão state, after a 4.6 mb mainshock on January 3, 2017. The focal mechanism solution indicates a strike slip fault with compression parallel to the cost line in agreement with previous studies. The aftershock activity was very intense in the begin fading to just few events after couple of days and the aftershock network only registered 60 events within two months. Hypocentral location of 10 events showed a possible trace of the fault in agreement with focal mechanism solution. The relocation of the main event with station correction and fixed depth was located within the aftershock cluster with accuracy of a GT5 event requirements.
7th International Congress of the Brazilian Geophysical Society
Proceedings of the 7 Simpósio Brasileiro de Geofísica
The present study introduces the first steps of a Support Vector Machine (SVM) algorithm using tw... more The present study introduces the first steps of a Support Vector Machine (SVM) algorithm using two discrimination features: spectral ratio and waveform complexity on a dataset characterized by lower magnitude events recorded by a local network in Minas Gerais State, Brazil. The selected data set consists of 43 microearthquakes and 39 mining blasts of similar magnitudes and locations. The analysis was carried out using data of vertical short period components of two 3C seismic stations. Our results revealed that despite of some overlapping, these techniques show a good capacity to discriminate artificial by natural events for the studied region. However, for short distances (~3 km), the technique deserves more attention.
Proceedings of the 6 Simpósio Brasileiro de Geofísica
Este trabalho apresentou os resultados das análises dos dados recentes da rede sísmica de Montes ... more Este trabalho apresentou os resultados das análises dos dados recentes da rede sísmica de Montes Claros. Observou-se que nos primeiros meses de 2014 (até 11 de abril) houve uma reativação da sismicidade com uma migração dos epicentros para o noroeste, se afastando da cidade. Isto indica uma maior extensão da falha sismogênica. A inversão de formas de ondas em duas estações da rede indica que os regimes de esforços para sismicidade atual e aquela observada até junho de 2013 são semelhantes.
Proceedings of the 7 Simpósio Brasileiro de Geofísica
In this paper we present the results of the Focal Mechanisms (FM) determination for four weak eve... more In this paper we present the results of the Focal Mechanisms (FM) determination for four weak events from the Goiás-Tocantins Seismic Zone (GTSZ) using the method of Cyclic Scanning of the Polarity Solutions (CSPS), such method makes use of the full waveform inversion to constrain the non-unique focal mechanism solutions, obtained by the FOCMEC program, from a set of few available polarities only. The solution reliability is controlled by a series of quality control parameters. The events occurred in the Brazil Central region, close to the cities of Mara Rosa/GO