Principal stress directions on the Atlantic continental shelf inferred from the orientations of borehole elongations

Dart, Richard L.; Zoback, Mary Lou

doi:10.3133/ofr87283

Cited by 11 publications

(6 citation statements)

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“…In northeastern Brazil, strike-slip focal mechanisms and the distribution of seismicity suggest a combination of plate-wide "regional" forces (such as asthenospheric drag or ridge-push) with local sources of stress (due to density contrasts across continental margins and sediment loading at the marginal basins). A similar combination of regional and local stresses was also observed in the Atlantic continental shelf of North America [Dart and Zoback, 1987;Zoback and Zoback, 1989].…”

Section: Blished (See Mercier Et Al [This Issue] For a Detailed Descsupporting

confidence: 62%

The regional intraplate stress field in South America

Assumpção¹

1992

J. Geophys. Res.

179

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A compilation of lithospheric stress directions for continental South America and the inferred major patterns of the regional intraplate stress field are presented. Stress orientations are based primarily on earthquake focal mechanisms and Quaternary fault slip inversion published in the literature. Four new focal mechanisms based on short‐period P wave modeling, and selected centroid‐moment‐tensor solutions (published by U.S. Geological Survey) consistent with P wave first motions at South American and other World‐Wide Standard Seismograph Network stations are also included in the data base. The observed patterns of intraplate stresses may be useful in constraining numerical models of the plate driving forces in the South American plate. In the Andean plateau (altitudes greater than 3000 m), N‐S extensional stresses predominate. E‐W compressional stresses are observed in the sub‐Andean and platform regions extending up to about 1000 km east of the Andes. The maximum horizontal stress (SHmax) is uniformly oriented in the E‐W direction throughout western South America. Averages of the SHmax direction at grid points spaced 2.5° were taken as representing the “regional” field. The E‐W direction of this regional field is not affected by the change of strike of the Andean chain nor by the contact of a flat subducted slab underneath. The regional SHmax direction is oriented 15° more clockwise than the direction of the Nazca plate convergence. The difference between the regional SHmax orientations and the absolute plate motion may be only about 6°. This may indicate that contact forces with the Nazca plate may not be the only major contributor to the intraplate stresses in western South America. The eastern limit of this Andean stress province seems to coincide with aseismic regions in the Upper Amazon basin and in the Parana basin. In the central Amazonian region, seismicity and stress data suggest a seismic province with N‐S compressional stresses. The origin of these stresses is not yet clearly understood but could possibly be related to lower crustal loading along the middle Amazon basin. In northeastern Brazil, seismicity is characterized by upper crustal strike‐slip earthquakes bordering the Potiguar marginal basin. A model is proposed for this region in which the stress field is the result of a superposition of regional E‐W compressional stresses and local extensional stresses (oriented perpendicular to the continental margin) possibly related to density contrasts and sediment loading in the continental shelf.

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Section: Blished (See Mercier Et Al [This Issue] For a Detailed Descsupporting

confidence: 62%

The regional intraplate stress field in South America

Assumpção¹

1992

J. Geophys. Res.

179

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“…The data presented here confirm the preliminary suggestions of Assumpção (1992) that the onshore stress field is the superposition of a regional, uniform E–W compressional stress with local extensional stresses in the upper crust normal to the coast. A combination of regional and local stresses has also been observed in the Atlantic continental shelf of North America Dart & Zoback 1987; Zoback & Zoback 1989). The regional compressive stress is related to the plate‐driving forces, and the local extensional stresses are generated at the continent–ocean structural transition.…”

Section: Stress Patternsmentioning

confidence: 89%

Superposition of local and regional stresses in northeast Brazil: evidence from focal mechanisms around the Potiguar marginal basin

Ferreira¹,

Oliveira²,

Takeya³

et al. 1998

Geophysical Journal International

144

103

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One of the most important seismic areas in Brazil is the northeastern region with earthquake activity occurring mainly in the exposed Precambrian basement around the Potiguar Mesozoic marginal basin. Since 1986, temporary seismographic networks have been deployed at many sites near the border of the Potiguar basin and also further inland. This instrumental effort has allowed a better understanding of the seismicity patterns and crustal stresses in the region. The seismicity in NE Brazil occurs mainly in swarms (lasting from months to many years) with shallow earthquakes (depths <12 km). These features and the large number of granitic/gneissic outcrops of the Precambrian basement allowed us to obtain good quality seismographic records, with clear P and S arrivals. Even with few stations and analogue recordings, reliable hypocentres and composite focal mechanisms have been determined with simple velocity models. The seismicity shows poor correlation with mapped faults. Several composite and single focal‐mechanism solutions were determined: strike‐slip faulting predominates in the area. Most nodal‐plane solutions are in good agreement with the fault planes determined from the distribution of hypocentres. The principal stress directions, obtained with inversion of focal mechanisms, show a strike‐slip stress field in the upper crust with maximum stress orientation ranging from SE–NW to E–W, roughly parallel to the northern coastline. Well‐bore breakouts in the Potiguar basin also show that the maximum horizontal compression is roughly parallel to the northern coast line. It is suggested that this pattern is the superposition of E–W compressional regional stresses, generated mainly by ridge push and collisional boundary forces on the South American plate, with local extensional stresses perpendicular to the coast, generated both by the continent—ocean structural transition and by flexural forces from sediment loading at the continental shelf.

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“…Thus, analyzing borehole breakouts, we determined the orientation of S, max at 20 locations in different parts of the Indian subcontinent including the Himalayan foothills and the Bombay offshore area [Gowd and Srirama Rao, 1989]. Borehole elongations were determined from four-arm dipmeter logs of oil exploration wells following the criteria for identifying breakout zones described by Dart [ 1985] and Dart and Zoback [ 1987].…”

Section: Stress Datamentioning

confidence: 99%

Tectonic stress field in the Indian subcontinent

Gowd¹,

Sathuluri²,

Gaur³

1992

J. Geophys. Res.

155

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A map of maximum horizontal compressive stress orientation in the Indian subcontinent has been prepared using orientations derived from three different stress indicators: borehole elongation breakouts, in situ hydraulic fracturing measurements, and earthquake focal mechanisms. Most part of the subcontinent appears to be characterized by a compressional stress regime (thrust and strikeslip faulting) imposed by plate boundary forces although SHmax orientations do not, in general, show clear correlation with the direction of motion of the Indian plate. Four provinces are recognized on the basis of regionally consistent orientations. These are the midcontinent stress province, the southern shield, the Bengal basin, and the Assam wedge. Their boundaries have been determined taking into consideration regional tectonics and seismicity. Central and northern India, including the Shillong Plateau stretching up to the great Himalaya, Pakistan, and Nepal are included in a broad “midcontinent” stress province characterized by NNE‐ENE oriented SHmax. The mean orientation of SHmax in this province is N23°E, subparallel to the direction of compression expected to arise from the net resistive forces at the Himalayan collision zone, suggesting that it is largely determined by the tectonic collision processes. Much of southern India (Mysore plateau and the high‐grade metamorphic terrain south of the plateau) appears to be part of a second stress province characterized by NW oriented SHmax. These appear close to those of the intraplate stress field prevailing in the central Indian Ocean. A third stress province was recognized in the Bengal basin including parts of West Bengal, Tripura, Manipur, and Mizoram in northeastern India and most of Bangladesh. This province extends eastward from the marginal fault in the western margin of the Bengal basin to the Indo‐Burma subduction zone and is bounded on the north by the E‐W striking Dauki fault. SHmax within the sedimentary pile of the Bengal basin is oriented in E‐W direction, while P axes of earthquakes within the basement and the crust beneath the basin and within the subducted slab of the Indian plate beneath the Indo‐Burman ranges generally trend north ‐ N30°E. SHmax orientations within the sedimentary pile of the basin are parallel to the local (approximately E‐W) direction of the convergence of Indian and Burmese plates, suggesting a casual relation to the resistive forces at the subduction zone in the Indo‐Burma region. Interestingly, the stress field in the basement and the crust beneath the Bengal basin and in the subducted slab is similar to the one prevailing in the midcontinent stress province. Assam wedge stress region occupies the northeastern corner of the Indian plate, including Upper Assam, Arunachal Pradesh, and much of Nagaland. This region subducts beneath a sharply bent continental collision boundary consisting of the northeastern limb of the Himalayan and northern limb of the Indo‐Burman fold belts. As a result, the stress field in this province is depth‐differentia...

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Principal stress directions on the Atlantic continental shelf inferred from the orientations of borehole elongations

Cited by 11 publications

References 50 publications

The regional intraplate stress field in South America

The regional intraplate stress field in South America

Superposition of local and regional stresses in northeast Brazil: evidence from focal mechanisms around the Potiguar marginal basin

Tectonic stress field in the Indian subcontinent

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