Patterns of stress and strain rate in southern Africa

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dc.contributor.authorBird, Peter
dc.contributor.authorBen-Avraham, Zvi
dc.contributor.authorSchubert, Gerald
dc.contributor.authorAndreoli, Marco
dc.contributor.authorViola, Giulio
dc.date.accessioned2021-10-08T07:04:27Z
dc.date.available2021-10-08T07:04:27Z
dc.date.issued2006
dc.description.abstractThe southward propagation of the East Africa rift presents an opportunity to study plate boundary formation. We tabulate orientation data which confirm the province of NW-SE directed most compressive horizontal principal stress (Wegener stress anomaly) earlier tentatively attributed to ridge push. We also collect information on stress regime, described by the associated Andersonian fault type(s). We use thin shell finite element models with realistic rheology to test three causes of stress: (1) lateral variations in density moment, (2) resistance of unbroken lithosphere to relative plate rotation, and (3) stress concentration ahead of a crack tip. Models with stress due primarily to variations in density moment are unsuccessful in their predictions (59-73% incorrect regimes; 32-40° azimuth errors). Models in which Africa-Somalia spreading is regulated at realistic rates by remote boundary conditions are more accurate (18-41% incorrect regimes; 25-35° azimuth errors). Treating the East Africa rift as a frictionless crack degrades the fit in either case. Apparently, the Wegener stress anomaly is caused primarily by resistance to the relative rotation between the Somalia and Africa plates. The East Africa rift north of 21°S may be weakened by strain but has residual friction ≥0.1. Greater strength of oceanic lithosphere is likely to cause stress increases, reorientations, and regime changes offshore. The predicted strain rate map has high rates along the rift, curving at 12°S into a western arc through Angola-Namibia-South Africa. Seismic hazard in Namibia may be greater than the instrumental catalog suggests. However, a number of unfit data indicate that these models represent only a first step.
dc.identifier.apacitationBird, P., Ben-Avraham, Z., Schubert, G., Andreoli, M., & Viola, G. (2006). Patterns of stress and strain rate in southern Africa. <i>Journal of Geophysical Research</i>, 111(B8), 174 - 177. http://hdl.handle.net/11427/34508en_ZA
dc.identifier.chicagocitationBird, Peter, Zvi Ben-Avraham, Gerald Schubert, Marco Andreoli, and Giulio Viola "Patterns of stress and strain rate in southern Africa." <i>Journal of Geophysical Research</i> 111, B8. (2006): 174 - 177. http://hdl.handle.net/11427/34508en_ZA
dc.identifier.citationBird, P., Ben-Avraham, Z., Schubert, G., Andreoli, M. & Viola, G. 2006. Patterns of stress and strain rate in southern Africa. <i>Journal of Geophysical Research.</i> 111(B8):174 - 177. http://hdl.handle.net/11427/34508en_ZA
dc.identifier.issn0022-1406
dc.identifier.issn0148-0227
dc.identifier.issn1934-2098
dc.identifier.issn2156-2202
dc.identifier.ris TY - Journal Article AU - Bird, Peter AU - Ben-Avraham, Zvi AU - Schubert, Gerald AU - Andreoli, Marco AU - Viola, Giulio AB - The southward propagation of the East Africa rift presents an opportunity to study plate boundary formation. We tabulate orientation data which confirm the province of NW-SE directed most compressive horizontal principal stress (Wegener stress anomaly) earlier tentatively attributed to ridge push. We also collect information on stress regime, described by the associated Andersonian fault type(s). We use thin shell finite element models with realistic rheology to test three causes of stress: (1) lateral variations in density moment, (2) resistance of unbroken lithosphere to relative plate rotation, and (3) stress concentration ahead of a crack tip. Models with stress due primarily to variations in density moment are unsuccessful in their predictions (59-73% incorrect regimes; 32-40° azimuth errors). Models in which Africa-Somalia spreading is regulated at realistic rates by remote boundary conditions are more accurate (18-41% incorrect regimes; 25-35° azimuth errors). Treating the East Africa rift as a frictionless crack degrades the fit in either case. Apparently, the Wegener stress anomaly is caused primarily by resistance to the relative rotation between the Somalia and Africa plates. The East Africa rift north of 21°S may be weakened by strain but has residual friction ≥0.1. Greater strength of oceanic lithosphere is likely to cause stress increases, reorientations, and regime changes offshore. The predicted strain rate map has high rates along the rift, curving at 12°S into a western arc through Angola-Namibia-South Africa. Seismic hazard in Namibia may be greater than the instrumental catalog suggests. However, a number of unfit data indicate that these models represent only a first step. DA - 2006 DB - OpenUCT DP - University of Cape Town IS - B8 J1 - Journal of Geophysical Research LK - https://open.uct.ac.za PY - 2006 SM - 0022-1406 SM - 0148-0227 SM - 1934-2098 SM - 2156-2202 T1 - Patterns of stress and strain rate in southern Africa TI - Patterns of stress and strain rate in southern Africa UR - http://hdl.handle.net/11427/34508 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/34508
dc.identifier.vancouvercitationBird P, Ben-Avraham Z, Schubert G, Andreoli M, Viola G. Patterns of stress and strain rate in southern Africa. Journal of Geophysical Research. 2006;111(B8):174 - 177. http://hdl.handle.net/11427/34508.en_ZA
dc.language.isoeng
dc.publisher.departmentDepartment of Geological Sciences
dc.publisher.facultyFaculty of Science
dc.sourceJournal of Geophysical Research
dc.source.journalissueB8
dc.source.journalvolume111
dc.source.pagination174 - 177
dc.source.urihttps://dx.doi.org/10.1029/2005JB003882
dc.subject.otherstrength
dc.subject.otherfriction
dc.subject.otherstrain
dc.subject.otherplates
dc.subject.otherboundary conditions
dc.subject.othererrors
dc.subject.otherprediction
dc.subject.otherfissures
dc.subject.otherconcentration
dc.subject.otherplate rotation
dc.subject.otherlithosphere
dc.subject.otherdensity
dc.subject.otherlateral variations
dc.subject.otherrheology
dc.subject.othermodels
dc.subject.otherfinite element analysis
dc.subject.otherThin shell
dc.subject.otherfaults
dc.subject.otheranomalies
dc.subject.otherorientation
dc.subject.otherplate boundaries
dc.subject.otherpropagation
dc.subject.otherStrain rate
dc.subject.otherstrain rates
dc.subject.otherPrincipal stress
dc.subject.otherSouth Africa
dc.subject.otherNamibia
dc.titlePatterns of stress and strain rate in southern Africa
dc.typeJournal Article
uct.type.publicationResearch
uct.type.resourceJournal Article
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