Seismicity patterns and focal mechanisms in southeastern Brazil

Assumpção, M.; Barbosa, José Roberto; Berrocal, Jesús; Bassini, Ailton; Veloso, J.A.V.; Mârza, Vasile; Huelsen, Mônica G. Von; Ribotta, L. C.

doi:10.1590/s0102-261x1997000200002

Cited by 16 publications

(12 citation statements)

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“…4 shows the effective elastic thickness (Te), available from Bizzi et al (2003) and the strain/ stress regime in the study area, available from Assumpção et al (1985Assumpção et al ( , 1997, Lima et al (1997), Assumpção (1998), Chimpliganond et al (2010), Marotta et al (2013), andAgurto-Detzel et al (2015). Fig.…”

Section: Resultsmentioning

confidence: 99%

“…b) Strain rate estimated by geodetic observations (Marotta et al, 2013). c) Stress estimated by focal mechanism (FM), breakout (BO), in situ measurements (IS) and geological fault analysis (GF), showed by Assumpção et al (1985Assumpção et al ( , 1997, Lima et al (1997), Assumpção (1998), Chimpliganond et al (2010), Marotta et al (2013), andAgurto-Detzel et al (2015). d) Predominant directions of strain rate and stress for the profile (vertical cross-section Z-Z') region shown in Figs.…”

Section: Discussionmentioning

confidence: 99%

“…The completeness of the BSB is variable in time and space, mainly due the inhomogeneous station density, which increased significantly only from the late 1970s with the installation of many stations in areas of hydroelectric reservoirs, and with another significant increase from 2011, with the installation of permanent stations of the BSN . According to Assumpção et al (1997) the Magnitude of Completeness value for the BSB is 3.2 for events starting from 1980 and 2.8 for events starting from 1990 being higher for prior periods (e.g. 4.5 for 1968, when beginning the operation of the stations arrangement in the capital, Brasília).…”

Section: Methodsmentioning

confidence: 99%

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Causes of intraplate seismicity in central Brazil from travel time seismic tomography

et al. 2016

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Causes of intraplate seismicity in central Brazil from travel time seismic tomography

et al. 2016

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“…A diffuse belt of seismicity occurs near or beyond the Cretaceous hinge line (Fig. 16) where the continental crust becomes highly extended (Assumpção, 1998;Assumpção et al, 2011Assumpção et al, , 2014; see maps by Assumpção et al, 1997, Zalán & Oliveira, 2005Zalán et al, 2011). Several of its earthquakes were characterized by compressional focal-plane mechanisms and had well-located hypocenters that indicated middle or upper crustal depths (Assumpção et al, 2011).…”

Section: The Model Abroadmentioning

confidence: 99%

“…This is particularly so in the light of current concepts of how extended margins evolve. Other newly reinterpreted, non-glaciated, hyperextended margins such as Southeast Brasil also display seismicity in association with onshore escarpments and offshore sedimentary basins (Riccomini et al, 1989;Assumpção, 1992Assumpção, , 1998Assumpção et al, 1997Assumpção et al, , 2011Riccomini & Assumpção, 1999;Bezerra & Vita-Finzi, 2000;Bezerra et al, 2008Bezerra et al, , 2014. In this paper we focus on how patterns of Scandinavian seismicity can be interpreted within the context of a specific geologic model that describes the evolution of the Scandinavian rifted margin from Mesozoic extension to the present-day.…”

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confidence: 99%

Some remarks on the earthquakes of Fennoscandia: A conceptual seismological model drawn from the perspective of hyperextension

Redfield¹,

Osmundsen²

2015

NJG

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To a first order, patterns of Fennoscandia's seismicity reflect the benchmark domain boundaries of its Mesozoic rifted margin. Three distinct belts of earthquakes strike sub-parallel to the generalized line of breakup. The outermost seismic belt (SB1) marks the Taper Break (TB), or the zone of flexural coupling/decoupling between the distal (seaward) and proximal/necking (landward) domains. A coastal belt (SB2) follows the Innermost Limit of Extension, defined as the onset of 39 km-thick crystalline continental crust. An interior belt (SB3) follows the Hinterland Break in Slope, or the landward limit of the Scandinavian rifted margin. Between each belt, large portions of the necking, proximal, and hinterland domains are seismically quiescent. Evaluation of the 'Cumulative Seismic Moment' (CSM w ) per unit area indicates that the release of seismic energy is asymmetric. Although some of Fennoscandia's largest seismic events occur in the dominantly Proterozoic to Archean lithosphere of the eastern craton, 80% of Fennoscandian CSM w maps to the domain boundaries of the western rifted margin. CSM w energy tends to be highest at the TB and decreases system atically towards the continental interior.As proposed by many previous studies, a first-order spatial correlation between Scandinavia's offshore earthquake belt and voluminous, geo logically rapid, sedimentary loading during the Neogene period is evident. However, the presence of thinned, faulted crystalline basement is also a very important factor behind Scandinavia's offshore seismicity. Where the Neogene deposits are at their thickest the underlying crust is dominantly oceanic; CSM w is lower per unit area there than where lesser Plio-Pleistocene loading impacts continental crust that was fully prepared by Mesozoic necking and hyperextension. CSM w data suggest that the 'strength' of the TB and the continental margin's distal domain is significantly less than that of relatively young (ca. 54 Ma) oceanic lithosphere. Our data imply that ridge push does not contribute significantly to Fennoscandia's seismicity. Rather, we find that thin-plate bending stresses stemming from offshore depositional loading conspire with unbuttressed Gravitational Potential Energy (GPE), onshore erosion, and post-glacial isostatic rebound to generate Fennoscandia's earthquakes.We present a conceptual seismological model for Fennoscadia that is consistent with modern hypotheses of extended margin evolution, including post-breakup reactivation by footwall uplift in regions adjacent to sharp crustal taper. Illustrated by simple concepts of elastic thin-plate theory, the model honors our conclusion that Fennoscandian seismicity is principally the product of locally derived stress fields and that far field stress from the oceanic domain is unlikely to penetrate deeply into a hyperextended continental margin. It predicts the locations of the observed seismic belts and seismic gaps with the mathematics of thin-plate bending. It describes how the outer seismic belt will remain localized in the...

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