Fault plane solutions of intraplate earthquakes in brazil: Some constraints on the regional stress field

Assumpção, M.; Suárez, Gerardo; Veloso, JoséAlberto

doi:10.1016/0040-1951(85)90201-x

Cited by 43 publications

(20 citation statements)

References 11 publications

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“…7), which allows a best fit to the observed boundary between the Grajaú Basin and the Araguaia Belt. This scenario would imply in a N-S direction of extension, which is in accordance with available seismic data (Assumpção et al, 1985). Given that the abrupt change of elevation in the swath profile corresponds to the E-W inflexion of the Tocantins river, this adds to the hypothesis of a major drainage capture in the lower Tocantins and of tectonic influence in the landform configuration of the study area.…”

Section: Resultssupporting

confidence: 85%

“…The epicenters are concentrated around the dam and roughly distributed along a N-Strending Precambrian reverse fault (Tocantins-Araguaia Lineament). Farther North, in the Marajó Island (Amazon River mouth), a m b 4.8 earthquake with a NNW-SSE direction of extension and an ENE-SSW direction of compression was recorded on August 1977 (Assumpção et al, 1985). These data indicate a present-day, roughly N-S direction of extension in the region.…”

Section: Study Areamentioning

confidence: 89%

“…1). Around the town of Redenção two events with m b 4.7 and 4.2 occurred in December 1980 and November 2010, respectively, the first with a normal-fault focal mechanism and a general N-S direction of extension (Assumpção et al, 1985). A set of induced earthquakes occurred between November 1985 and March 1988 after the impoundment of the Tucuruí reservoir, the larger with m b 3.6, but no focal mechanisms were obtained for these events (Assumpção et al, 2001).…”

Section: Study Areamentioning

confidence: 96%

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Regional scale analysis of landform configuration with base-level (isobase) maps

Grohmann¹,

Riccomini²,

Chamani³

2011

Hydrol. Earth Syst. Sci.

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Abstract. Base-level maps (or "isobase maps", as originally defined by Filosofov, 1960), express a relationship between valley order and topography. The base-level map can be seen as a "simplified" version of the original topographic surface, from which the "noise" of the low-order stream erosion was removed. This method is able to identify areas with possible tectonic influence even within lithologically uniform domains. Base-level maps have been recently applied in semi-detail scale (e.g., 1:50 000 or larger) morphotectonic analysis. In this paper, we present an evaluation of the method's applicability in regional-scale analysis (e.g., 1:250 000 or smaller). A test area was selected in northern Brazil, at the lower course of the Araguaia and Tocantins rivers. The drainage network extracted from SRTM30 PLUS DEMs with spatial resolution of approximately 900 m was visually compared with available topographic maps and considered to be compatible with a 1:1,000 000 scale. Regarding the interpretation of regional-scale morphostructures, the map constructed with 2nd and 3rd-order valleys was considered to present the best results. Some of the interpreted base-level anomalies correspond to important shear zones and geological contacts present in the 1:5 000 000 Geological Map of South America. Others have no correspondence with mapped Precambrian structures and are considered to represent younger, probably neotectonic, features. A strong E-W orientation of the base-level lines over the inflexion of the Araguaia and Tocantins rivers, suggest a major drainage capture. A N-S topographic swath profile over the Tocantins and Araguaia rivers reveals a topographic pattern which, allied with seismic data showing a roughly N-S direction of extension in the area, lead us to interpret this lineament as an E-W, southward-dipping normal fault. There is also a good visual correspondence between the base-level lineaments and Correspondence to: C. H. Grohmann (guano@usp.br) geophysical anomalies. A NW-SE lineament in the southeast of the study area partially corresponds to the northern border of the Mosquito lava field, of Jurassic age, and a NW-SE lineament traced in the northeastern sector of the study area can be interpreted as the Picos-Santa Inês lineament, identifiable in geophysical maps but with little expression in hypsometric or topographic maps.

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Section: Resultssupporting

confidence: 85%

Section: Study Areamentioning

confidence: 89%

Section: Study Areamentioning

confidence: 96%

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Regional scale analysis of landform configuration with base-level (isobase) maps

Grohmann¹,

Riccomini²,

Chamani³

2011

Hydrol. Earth Syst. Sci.

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show abstract

“…Only a handful of studies on the regional stress field exist (e.g. Assumpção et al 1985;Assumpção & Suárez 1988;Assumpção 1998a,b), and few focal mechanisms and other types of measures, such as borehole breakouts and other in situ measurements, have been published for this region. Thus, it is important to maximize the use of any new seismological data for this area of Brazil that could lead to a better understanding of the dominant seismotectonics and stress field in mid-plate South America.…”

Section: Introductionmentioning

confidence: 99%

The 2012–2013 Montes Claros earthquake series in the São Francisco Craton, Brazil: new evidence for non-uniform intraplate stresses in mid-plate South America

Agurto‐Detzel

Assumpção

Ciardelli

et al. 2014

Geophysical Journal International

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an m b = 4 earthquake shook the town of Montes Claros, Brazil in the middle of the São Francisco Craton. Because of the scarce seismicity in the area, an event like this could provide valuable information to characterize the governing seismotectonics and stress field for the region. Here, we present the results of more than 1 yr of local seismic monitoring after the main shock. We found that the seismicity originated at approximately 1-km depth in an NNW-oriented blind reverse fault, dipping to the E. The magnitude of the main shock was 4m b , with aftershocks reaching up to 3.6m b . Focal mechanisms from first motion polarities and waveform moment tensor inversions indicate a reverse faulting in agreement with the orientation of the aftershock locations. In addition, we derived a new 1-D local velocity model using a simultaneous inversion of hypocentres and velocity layers. The results indicate P-wave velocities of 4.5 km s −1 for the upper layer of carbonate rocks and 5.23 and 5.69 km s −1 for the lower fractured and compact crystalline basement layers, respectively. Higher Vp/Vs ratios were obtained for the upper two layers compared to the lowermost layer, possibly indicating presence of rock fracturing and percolated water. The calculated stress drop for the main event is 0.33 MPa, which is a relatively low value for an intraplate earthquake but still within the observed range. The inversion of the main shock focal mechanism and previously published focal mechanisms suggests a compressional stress regime in the central part of the São Francisco Craton, which is different from the strike-slip regime in the southern part, although both have an EW-oriented σ 1. On the other hand, focal mechanisms of events located to the west of the craton indicate an NW-SE oriented σ 1 for central Brazil. This variability highlights the importance of local sources of stresses (e.g. flexural stresses) in mid-plate South America, unlike other mid-plate areas of the world, such as central and east North America, where a more uniform stress field is observed.

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“…No interior do Brasil, os dados existentes são insuficientes ainda para melhor classificar a participação da subducção Β na sismicidade intracontinental (ASSUMPÇÃO et al, 1985), como se espera vir a ser demonstrado, a não ser localmente. Estas manifestações no remoto interior da placa (algumas distando mais de 1400 km da cinta de empurrões da antefossa subandina, atrás do arco magmático), de identificação recente, são muito importantes -para a acumulação comercial de gás, por exemplo no caso amazônico -abrindo perspectivas de armadilhas estruturais nas bacias interiores e um enorme campo de investigações de tectônica de embasamento e cobertura no interior das plataformas.…”

Section: Tipos Básicos De Arcos Magmáticosunclassified

O Fenômeno da ativação no contexto da tectônica global

Neves

1992

Bol. IG-USP, Sér. didát.

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Fault plane solutions of intraplate earthquakes in brazil: Some constraints on the regional stress field

Cited by 43 publications

References 11 publications

Regional scale analysis of landform configuration with base-level (isobase) maps

Regional scale analysis of landform configuration with base-level (isobase) maps

The 2012–2013 Montes Claros earthquake series in the São Francisco Craton, Brazil: new evidence for non-uniform intraplate stresses in mid-plate South America

O Fenômeno da ativação no contexto da tectônica global

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