Albini P.,Italian National Institute of Geophysics and Volcanology |
Strasser F.O.,Council for Geoscience CGS |
Flint N.S.,University of the Western Cape
Bulletin of Earthquake Engineering | Year: 2014
The seismicity of Grahamstown, in the Eastern Cape Province of South Africa, for the years between 1820 and 1936 is investigated with recourse to contemporaneous documentary sources, leading to the development of a seismic history incorporating consideration of the broader geo-political context. Individual studies of five regional events that were felt in Grahamstown during that period, and of one that was not, are presented. Each study includes the development of a full set of intensity data points, which are used to determine reappraised epicentral locations and magnitudes, some of which differ significantly from previously listed parameters. The results thus obtained highlight the value of seeking out additional contemporary sources from different language groups when revisiting the source parameters of earthquakes for which no or only very limited instrumental information is available. © The Author(s) 2013.
Fritz H.,University of Graz |
Abdelsalam M.,Oklahoma State University |
Ali K.A.,King Abdulaziz University |
Bingen B.,Geological Survey of Norway |
And 12 more authors.
Journal of African Earth Sciences | Year: 2013
The East African Orogen, extending from southern Israel, Sinai and Jordan in the north to Mozambique and Madagascar in the south, is the world́s largest Neoproterozoic to Cambrian orogenic complex. It comprises a collage of individual oceanic domains and continental fragments between the Archean Sahara-Congo-Kalahari Cratons in the west and Neoproterozoic India in the east. Orogen consolidation was achieved during distinct phases of orogeny between ~850 and 550. Ma. The northern part of the orogen, the Arabian-Nubian Shield, is predominantly juvenile Neoproterozoic crust that formed in and adjacent to the Mozambique Ocean. The ocean closed during a protracted period of island-arc and microcontinent accretion between ~850 and 620. Ma. To the south of the Arabian Nubian Shield, the Eastern Granulite-Cabo Delgado Nappe Complex of southern Kenya, Tanzania and Mozambique was an extended crust that formed adjacent to theMozambique Ocean and experienced a ~650-620. Ma granulite-facies metamorphism. Completion of the nappe assembly around 620. Ma is defined as the East African Orogeny and was related to closure of the Mozambique Ocean. Oceans persisted after 620. Ma between East Antarctica, India, southern parts of the Congo-Tanzania-Bangweulu Cratons and the Zimbabwe-Kalahari Craton. They closed during the ~600-500. Ma Kuungan or Malagasy Orogeny, a tectonothermal event that affected large portions of southern Tanzania, Zambia, Malawi, Mozambique, Madagascar and Antarctica. The East African and Kuungan Orogenies were followed by phases of post-orogenic extension. Early ~600-550. Ma extension is recorded in the Arabian-Nubian Shield and the Eastern Granulite-Cabo Delgado Nappe Complex. Later ~550-480. Ma extension affected Mozambique and southern Madagascar. Both extension phases, although diachronous,are interpreted as the result of lithospheric delamination. Along the strike of the East African Orogen, different geodynamic settings resulted in the evolution of distinctly different orogen styles. The Arabian-Nubian Shield is an accretion-type orogen comprising a stack of thin-skinned nappes resulting from the oblique convergence of bounding plates. The Eastern Granulite-Cabo Delgado Nappe Complex is interpreted as a hot- to ultra-hot orogen that evolved from a formerly extended crust. Low viscosity lower crust resisted one-sided subduction, instead a sagduction-type orogen developed. The regions of Tanzania and Madagascar affected by the Kuungan Orogeny are considered a Himalayan-type orogen composed of partly doubly thickened crust. © 2013 The Authors.