East African earthquakes below 20 km depth and their implications for crustal structure

Abstract. Deep seismic acquisitions and a new kinematic study recently highlighted the presence of continental crust in both the southern Mozambique's Coastal Plain (MCP) and further offshore in the North Natal Valley (NNV). Such findings falsify previous geodynamic scenarios based on the kinematic overlap between Antarctica and Africa plates, thus profoundly impacting our understanding East-Gondwana break-up. Using an updated position of Antarctica with respect to Africa this study reconsider the formation mechanism of East-African margins and most specifically of the Limpopo margin (LM). Coincident wide-angle and multi-channel seismic data acquired within the PAMELA project are processed to image the sedimentary and deep crustal structure along a profile that runs from the northeastern NNV to the Mozambique basin (MB) striking through the LM. This dataset is combined with companion deep seismic profiles and industrial onshore-offshore seismic lines to provide a robust scenario for the formation and evolution of the LM. Our P-wave velocity model consists of an upper sedimentary sequence of weakly compacted sediments including intrusions and lava flows in the NNV while contourites and mass transport deposits dominates the eastern edge of the LM. This sequence covers a thick acoustic basement that terminates as a prominent basement high just west of the contourites and mass transport deposits domain. The acoustic basement has a seismic facies and velocity signature typical of a volcano-sedimentary basin and appears widespread over our study area extending toward the eastern MCP and NNV. Based on industrial well logs that calibrate our tectono-stratigraphic analysis we constrain its age to be pre-Neocomian. We further infer that either strike-slip or trans-tensional deformation occurred at the basement high which sustained uplift up to the Neocomian. At depth, the crystalline basement and uppermost mantle velocity structures show a progressive eastward crustal thinning of continental crust along the edge of the MCP/NNV and up to the location of the basement high. On its eastern side, however, a corridor of anomalous crust depicts the velocity signature of a volcanic basement overlying lower continental crust. We infer that strike-slip rifting along the LM was accommodated at depth by ductile shearing responsible for the thinning of the continental crust and an oceanward flow of lower crustal material. This process was accompanied by intense magmatism that extruded to form the volcanic basement and gave to the corridor its peculiar structure and mixed nature. The whole region remained at a relative high level and a shallow marine environment dominated during this period. Only after break-up in the MB decoupling occurred between the MCP/NNV and the corridor allowing for the latter to subside and being covered by deep marine sediments. We provide new insights into the early evolution and formation of the LM that takes into account both kinematic and geological constraints. This scenario favors strike-slip rifting along the LM meaning that no changes in extensional direction occurred between the rifting and the opening of the MB.

Download Full-text

Crustal Structure of the East African Plateau and Rift Valleys from Gravity Measurements

Nature ◽

10.1038/223143a0 ◽

1969 ◽

Vol 223 (5202) ◽

pp. 143-146 ◽

Cited By ~ 34

Author(s):

W. T. C. SOWERBUTTS

Keyword(s):

Crustal Structure ◽

East African ◽

Gravity Measurements ◽

Rift Valleys

Download Full-text

Crustal structure of the East African Rift zone

Tectonophysics ◽

10.1016/0040-1951(73)90116-9 ◽

1973 ◽

Vol 20 (1-4) ◽

pp. 269-281 ◽

Cited By ~ 30

Author(s):

R.E. Long ◽

K. Sundaralingam ◽

P.K.H. Maguire

Keyword(s):

Crustal Structure ◽

Rift Zone ◽

East African Rift ◽

East African ◽

African Rift

Download Full-text

Crustal Structure of the East African Rift Zone

The Structure of the Earth's Crust - Based on Seismic Data - Developments in Geotectonics ◽

10.1016/b978-0-444-41191-4.50030-6 ◽

1974 ◽

pp. 269-281

Author(s):

R.E. LONG ◽

K. SUNDARALINGAM ◽

P.K.H. MAGUIRE

Keyword(s):

Crustal Structure ◽

Rift Zone ◽

East African Rift ◽

East African ◽

African Rift

Download Full-text

Supplementary material to "Crustal structure of the East-African Limpopo Margin, a strike-slip rifted corridor along the continental Mozambique Coastal Plain and North-Natal Valley"

10.5194/se-2020-209-supplement ◽

2021 ◽

Author(s):

Mikael Evain ◽

Philippe Schnürle ◽

Angélique Leprêtre ◽

Fanny Verrier ◽

Louise Watremez ◽

...

Keyword(s):

Crustal Structure ◽

Coastal Plain ◽

Strike Slip ◽

East African ◽

Supplementary Material

Download Full-text

Scanning electron microscopy of the integument of schistosoma rodhaini

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010014230x ◽

1986 ◽

Vol 44 ◽

pp. 132-133

Author(s):

P. Evers ◽

C. Schutte ◽

C. D. Dettman

Keyword(s):

Electron Microscopy ◽

Scanning Electron Microscopy ◽

Oral Sucker ◽

Adult Male ◽

Dorsal Surface ◽

Ventral Surface ◽

Sensory Receptors ◽

East African ◽

Dorsal Midline ◽

Scanning Electron

S.rodhaini (Brumpt 1931) is a parasite of East African rodents which may possibly hybridize with the human schistosome S. mansoni. The adult male at maturity measures approximately 3mm long and possesses both oral and ventral suckers and a marked gynaecophoric canal. The oral sucker is surrounded by a ring of sensory receptors with a large number of inwardly-pointing spines set into deep sockets occupying the bulk of the ventral surface of the sucker. Numbers of scattered sensory receptors are found on both dorsal and ventral surfaces of the head (Fig. 1) together with two conspicuous rows of receptors situated symmetrically on each side of the midline. One row extends along the dorsal surface of the head midway between the dorsal midline and the lateral margin.

Download Full-text

International Telesupervision: The Clinical Fellowship Experience

Perspectives of the ASHA Special Interest Groups ◽

10.1044/persp2.sig11.73 ◽

2017 ◽

Vol 2 (11) ◽

pp. 73-78

Author(s):

David W. Rule ◽

Lisa N. Kelchner

Keyword(s):

Graduate Students ◽

Clinical Supervision ◽

Rural Areas ◽

The United States ◽

Speech Language Pathology ◽

Access To Services ◽

East African ◽

The World ◽

Language Pathology ◽

National Certification

Telepractice technology allows greater access to speech-language pathology services around the world. These technologies extend beyond evaluation and treatment and are shown to be used effectively in clinical supervision including graduate students and clinical fellows. In fact, a clinical fellow from the United States completed the entire supervised clinical fellowship (CF) year internationally at a rural East African hospital, meeting all requirements for state and national certification by employing telesupervision technology. Thus, telesupervision has the potential to be successfully implemented to address a range of needs including supervisory shortages, health disparities worldwide, and access to services in rural areas where speech-language pathology services are not readily available. The telesupervision experience, potential advantages, implications, and possible limitations are discussed. A brief guide for clinical fellows pursuing telesupervision is also provided.

Download Full-text