Lithospheric structure beneath the Central Africa Orogenic Belt in Cameroon from the analysis of satellite gravity and passive seismic data

SUMMARY Current seismic tomography models show a complex environment underneath the crust, corroborated by high-precision satellite gravity observations. Both data sets are used to independently explore the density structure of the upper mantle. However, combining these two data sets proves to be challenging. The gravity-data has an inherent insensitivity in the radial direction and seismic tomography has a heterogeneous data acquisition, resulting in smoothed tomography models with de-correlation between different models for the mid-to-small wavelength features. Therefore, this study aims to assess and quantify the effect of regularization on a seismic tomography model by exploiting the high lateral sensitivity of gravity data. Seismic tomography models, SL2013sv, SAVANI, SMEAN2 and S40RTS are compared to a gravity-based density model of the upper mantle. In order to obtain similar density solutions compared to the seismic-derived models, the gravity-based model needs to be smoothed with a Gaussian filter. Different smoothening characteristics are observed for the variety of seismic tomography models, relating to the regularization approach in the inversions. Various S40RTS models with similar seismic data but different regularization settings show that the smoothening effect is stronger with increasing regularization. The type of regularization has a dominant effect on the final tomography solution. To reduce the effect of regularization on the tomography models, an enhancement procedure is proposed. This enhancement should be performed within the spectral domain of the actual resolution of the seismic tomography model. The enhanced seismic tomography models show improved spatial correlation with each other and with the gravity-based model. The variation of the density anomalies have similar peak-to-peak magnitudes and clear correlation to geological structures. The resolvement of the spectral misalignment between tomographic models and gravity-based solutions is the first step in the improvement of multidata inversion studies of the upper mantle and benefit from the advantages in both data sets.

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Shear wave velocity profile estimation by integrated analysis of active and passive seismic data from small aperture arrays

Journal of Applied Geophysics ◽

10.1016/j.jappgeo.2016.03.034 ◽

2016 ◽

Vol 130 ◽

pp. 37-52 ◽

Cited By ~ 13

Author(s):

A.M. Lontsi ◽

M. Ohrnberger ◽

F. Krüger

Keyword(s):

Velocity Profile ◽

Shear Wave ◽

Shear Wave Velocity ◽

Seismic Data ◽

Integrated Analysis ◽

Small Aperture ◽

Passive Seismic ◽

Shear Wave Velocity Profile ◽

Profile Estimation ◽

Aperture Arrays

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Pre-Katangan geochronology of Zambia and adjacent parts of Central Africa

Canadian Journal of Earth Sciences ◽

10.1139/e68-057 ◽

1968 ◽

Vol 5 (3) ◽

pp. 621-628 ◽

Cited By ~ 20

Author(s):

J. R. Vail ◽

N. J. Snelling ◽

D. C. Rex

Keyword(s):

Lake Tanganyika ◽

Central Africa ◽

New Age ◽

Orogenic Belt ◽

Eastern Africa ◽

Sedimentary Sequence ◽

Precambrian Rocks ◽

Late Precambrian ◽

Orogenic Belts ◽

Age Determinations

The significance of new age determinations on pre-Katangan (Late Precambrian) rocks and minerals from Zambia and adjacent parts of Tanzania and Rhodesia is discussed. In northwestern Rhodesia, the Lomagundi-Piriwiri sediments were deposited between 2500 and 2000 m.y. ago and were folded along meridional trends at circa 1940 m.y. A later episode of folding and metamorphism along similar trends occurred about 1700 m.y. ago, but only affected the western part of the sedimentary sequence (the Piriwiri Series). This latter date is comparable to that which appears to characterize the Tumbide trend, a N- to NE-trending fold system, in Zambia.In Zambia the Tumbide trend is the oldest tectonic episode preserved in the basement and is found only in isolated blocks and cores into which later tectonisms have not penetrated. The dominant pre-Katangan tectonism is represented by the NE to ENE Irumide trend. Such tectonic trends are particularly well developed in the Irumide Orogenic Belt of northern Zambia and adjacent Tanzania. Age determinations set a younger limit of circa 900 m.y. to this trend and the existence of an Irumide Cycle between about 1600 and 900 m.y. is suggested. The possibility that the relatively unmetamorphosed sediments of the Upper Plateau Series and Abercorn Sandstones at the southern end of Lake Tanganyika, the Mafingi Series of northern Malawi, and the Konse Series of Tanzania, represent near-contemporaneous platform deposition associated with the Irumide belt is considered.From this and other recent studies the distribution of orogenic belts in central and eastern Africa can be revised and a number of features of their pattern and inter-relationships noted.

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Seismic solutions utilizing existing in-mine infrastructure for mineral exploration: A case study from Maseve platinum mine, South Africa

The Leading Edge ◽

10.1190/tle41010054.1 ◽

2022 ◽

Vol 41 (1) ◽

pp. 54-61

Author(s):

Moyagabo K. Rapetsoa ◽

Musa S. D. Manzi ◽

Mpofana Sihoyiya ◽

Michael Westgate ◽

Phumlani Kubeka ◽

...

Keyword(s):

South Africa ◽

Seismic Data ◽

Mineral Exploration ◽

Ground Surface ◽

Seismic Survey ◽

Noisy Environment ◽

Borehole Data ◽

Passive Seismic ◽

Below Ground

We demonstrate the application of seismic methods using in-mine infrastructure such as exploration tunnels to image platinum deposits and geologic structures using different acquisition configurations. In 2020, seismic experiments were conducted underground at the Maseve platinum mine in the Bushveld Complex of South Africa. These seismic experiments were part of the Advanced Orebody Knowledge project titled “Developing technologies that will be used to obtain information ahead of the mine face.” In these experiments, we recorded active and passive seismic data using surface nodal arrays and an in-mine seismic land streamer. We focus on analyzing only the in-mine active seismic portion of the survey. The tunnel seismic survey consisted of seven 2D profiles in exploration tunnels, located approximately 550 m below ground surface and a few meters above known platinum deposits. A careful data-processing approach was adopted to enhance high-quality reflections and suppress infrastructure-generated noise. Despite challenges presented by the in-mine noisy environment, we successfully imaged the platinum deposits with the aid of borehole data and geologic models. The results open opportunities to adapt surface-based geophysical instruments to address challenging in-mine environments for mineral exploration.

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