African stress pattern from formal inversion of focal mechanism data

Delvaux, Damien; Barth, Andreas

doi:10.1016/j.tecto.2009.05.009

Cited by 276 publications

(277 citation statements)

References 62 publications

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“…Similarly, in the Rukwa basin to the north, stress inversion of earthquakes (Delvaux and Barth, 2010) shows Sh max is NW-SE, invoking an ENE-WSW extension regime today.…”

Section: Introductionmentioning

confidence: 94%

Implications of structural inheritance in oblique rift zones for basin compartmentalization: Nkhata Basin, Malawi Rift (EARS)

Mortimer

Paton

Scholz

et al. 2016

Marine and Petroleum Geology

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The Cenozoic East African Rift System (EARS) is an exceptional example of active continental extension, providing opportunities for furthering our understanding of hydrocarbon plays within rifts. It is divided into structurally distinct western and eastern branches. The western branch comprises deep rift basins separated by transfer zones, commonly localised onto pre-existing structures, offering good regional scale hydrocarbon traps. At a basin-scale, local discrete inherited structures might also play an important role on fault localisation and hydrocarbon distribution. Here, we consider the evolution of the Central basin of the Malawi Rift, in particular the influence of pre-existing structural fabrics.Integrating basin-scale multichannel 2D, and high resolution seismic datasets we constrain the border, Mlowe-Nkhata, fault system (MNF) to the west of the basin and smaller Mbamba fault (MF) to the east and document their evolution. Intra basin structures define a series of horsts, which initiated as convergent transfers, along the basin axis. The horsts are offset along a NE-SW striking transfer fault parallel to and along strike of the onshore Karoo 2 (Permo-Triassic) Ruhuhu graben. Discrete pre-existing structures probably determined its location and, oriented obliquely to the extension orientation it accommodated predominantly strike-slip deformation, with more slowly accrued dip-slip.To the north of this transfer fault, the overall basin architecture is asymmetric, thickening to the west throughout; while to the south, an initially symmetric graben architecture became increasingly asymmetric in sediment distribution as strain localised onto the western MNF. The presence of the axial horst increasingly focussed sediment supply to the west. As the transfer fault increased its displacement, so this axial supply was interrupted, effectively starving the south-east while ponding sediments between the western horst margin and the transfer fault. This asymmetric bathymetry and partitioned sedimentation continues to the present-day, overprinting the early basin symmetry and configuration. Sediments deposited earlier become increasingly dissected and fault juxtapositions changed at a small (10-100 m) scale. The observed influence of basin-scale transfer faults on sediment dispersal and fault compartmentalisation due to pre-existing structures oblique to the extension orientation is relevant to analogous exploration settings.

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“…Similarly, in the Rukwa basin to the north, stress inversion of earthquakes (Delvaux and Barth, 2010) shows Sh max is NW-SE, invoking an ENE-WSW extension regime today.…”

Section: Introductionmentioning

confidence: 94%

Implications of structural inheritance in oblique rift zones for basin compartmentalization: Nkhata Basin, Malawi Rift (EARS)

Mortimer

Paton

Scholz

et al. 2016

Marine and Petroleum Geology

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“…The boundary forces at the plates' sides and bases and the buoyancy forces from lateral variations in gravitational potential energy are responsible for this motion and the resultant horizontal stress field (Craig et al, 2011;Stamps et al, 2014; Figure 2A). A normal faulting regime (vertical stress component (σ v ) greater than the two horizontal stress components: σ v = σ 1 > σ 2 > σ 3 ) dominates in the EARS, with a strike slip regime (vertical stress component is intermediate relative to the horizontal stress components: σ 1 > σ v > σ 3 ) more evident in some places (e.g., Asal-Ghoubbet Rift, Delvaux and Barth, 2009). For the normal extensional regime, the direction of the maximum horizontal stress S HMAX = σ 2 , should correspond to the direction of dyke propagation, orthogonal to the opening direction or the minimum horizontal stress (S HMIN = σ 3 ).…”

Section: Factors That Could Affect Stress and Strain In The Earsmentioning

confidence: 99%

“…The stress field can be measured locally, but very sparsely, by several methods operating at different length scales (Amadei and Stephansson, 1997) from earthquake focal mechanisms (Delvaux and Barth, 2009), and seismic anisotropy (Kendall et al, 2005) over tens of kilometers, borehole breakouts at a meter scale and hydro-fracturing over tens to hundreds of meters (Heidbach et al, 2010). In the EARS these local measurements suggest a regional stress field associated with ∼100 km-long rift segments.…”

Section: Factors That Could Affect Stress and Strain In The Earsmentioning

confidence: 99%

Historical Volcanism and the State of Stress in the East African Rift System

et al. 2016

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Crustal extension at the East African Rift System (EARS) should, as a tectonic ideal, involve a stress field in which the direction of minimum horizontal stress is perpendicular to the rift. A volcano in such a setting should produce dykes and fissures parallel to the rift. How closely do the volcanoes of the EARS follow this? We answer this question by studying the 21 volcanoes that have erupted historically (since about 1800) and find that 7 match the (approximate) geometrical ideal. At the other 14 volcanoes the orientation of the eruptive fissures/dykes and/or the axes of the host rift segments are oblique to the ideal values. To explain the eruptions at these volcanoes we invoke local (non-plate tectonic) variations of the stress field caused by: crustal heterogeneities and anisotropies (dominated by NW structures in the Protoerozoic basement), transfer zone tectonics at the ends of offset rift segments, gravitational loading by the volcanic edifice (typically those with 1-2 km relief) and magmatic pressure in central reservoirs. We find that the more oblique volcanoes tend to have large edifices, large eruptive volumes, and evolved and mixed magmas capable of explosive behavior. Nine of the volcanoes have calderas of varying ellipticity, 6 of which are large, reservoir-collapse types mainly elongated across rift (e.g., Kone) and 3 are smaller, elongated parallel to the rift and contain active lava lakes (e.g., Erta Ale), suggesting different mechanisms of formation and stress fields. Nyamuragira is the only EARS volcano with enough sufficiently well-documented eruptions to infer its long-term dynamic behavior. Eruptions within 7 km of the volcano are of relatively short duration (<100 days), but eruptions with more distal fissures tend to have lesser obliquity and longer durations, indicating a changing stress field away from the volcano. There were major changes in long-term magma extrusion rates in 1977 (and perhaps in 2002) due to major along-rift dyking events that effectively changed the Nyamuragira stress field and the intrusion/extrusion ratios of eruptions.

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“…This program is free source program developed originally in DOS by Delvaux (1993) and then modified for Windows by Devaux and Sperner (2003). The graphical output of the stress inversion by the Win-Tensor program depicts the projection of the principal stress axes in a lower hemisphere equal-area projection and allows evaluating the overall quality of the result (Delvaux and Barth, 2010).…”

Section: Stereographic Projectionmentioning

confidence: 99%