Moctar Doucoure | Nelson Mandela Metropolitan University (original) (raw)

Papers by Moctar Doucoure

GSA Annual Meeting in Seattle, Washington, USA - 2017, 2017

EGUGA, May 1, 2010

Spatial and temporal variations in water storage can be attributed to the heterogeneous nature of... more Spatial and temporal variations in water storage can be attributed to the heterogeneous nature of the subsurface. In this paper, the properties of soil and fractured rock aquifers are examined for the example of the South African Gravimetric Observation Station (SAGOS) in Sutherland. Also, aspects of groundwater recharge and their implications for gravimetric observations are reviewed. First results obtained from a hydro-meteorological monitoring system that was installed about one and a half years ago in Sutherland, measuring climate variables, soil moisture and groundwater levels, are evaluated. The results will aid in the development of a local 3-D subsurface model and in interpreting the gravity residuals of the superconducting gravimeter in Sutherland.

Regional geology reviews, 2016

During August and September 2015, a seismic network consisting of 17 stations was installed in th... more During August and September 2015, a seismic network consisting of 17 stations was installed in the south-eastern Cape-Karoo region, near the town of Jansenville. Ambient seismic signals were continuously recorded for a three week period. In this chapter, we reconstruct estimates of the seismic Green’s functions between sensor pairs by cross-correlating the ambient seismic signals recorded in the vertical component of each station. The resulting Green’s functions contain clear direct Rayleigh wave arrivals. The measured group velocity dispersion curves of the Rayleigh waves were averaged in the period range from 2.5 to 5.5 s (approximately 2–5 km depth). The arrival times of the Rayleigh waves are picked at different periods and then inverted to compute 2-D group velocity maps. This resulted in a velocity model up to depths of 5 km. The results reveal two different velocity regions, broadly corresponding to the Cape Fold Belt and the flanking Karoo Basin. The higher group velocity anomalies (3–5 km in thickness) most likely represent the Carboniferous-Permian sequences of the Karoo Basin (Dwyka-Ecca-Beaufort Groups). A lowermost velocity region in the south-eastern study area could correspond to the Jurassic-Cretaceous sequences of the Algoa Basin that directly overlie the Cape Fold Belt.

AGU Spring Meeting Abstracts, May 1, 2001

South African Journal of Geology, Sep 1, 2017

The Karoo region of South Africa is an ideal laboratory to use ambient seismic signals to map the... more The Karoo region of South Africa is an ideal laboratory to use ambient seismic signals to map the shallow subsurface, as it is a quiet and pristine environment with a geology that is relatively well known. Ambient seismic signals were continuously recorded for a ten week period between August and October 2015. The ambient seismic noise network consisted of two groups of 17 temporary, stand-alone seismic stations each. These were installed in the southeastern Cape Karoo region, near the town of Jansenville. Here we present data on the retrieval and coherency of Rayleigh surface waves extracted from the vertical component recordings. We reconstruct and show, for the first time in the southeastern Cape Karoo, estimates of Green's function from cross-correlating ambient noise data between stations pairs, which can be successfully used to image the subsurface. The stacked cross-correlations between all station pairs show clear arrivals of the Rayleigh surface waves. The group velocities of the Rayleigh waves in the 3 to 7 seconds period range were picked and inverted to compute the 2-D group velocity maps. The resulting 2-D group velocity maps at different periods resulted in a group velocity model from approximately 2 to 7 km depth, which shows a high velocity anomaly in the north of the study area, most likely imaging the denser, thick sedimentary basin of the Karoo (Carboniferous-Permian). To the south, the low velocity anomaly could correspond to the overlying Jurassic-Cretaceous sedimentary sequences of the younger Algoa Basin (Uitenhage Group).

South African Journal of Science, 2021

Journal of Biogeography, 2020

AimFor 80 years, popular opinion has held that most of Madagascar's terrestrial vertebrates a... more AimFor 80 years, popular opinion has held that most of Madagascar's terrestrial vertebrates arrived from Africa by transoceanic dispersal (i.e. rafting or swimming). We reviewed this proposition, focussing on three ad hoc hypotheses proposed to render this unlikely scenario more feasible: (a) Could hibernation have helped mammals to reach Madagascar? (b) Could the aquatic abilities of hippopotamuses have enabled them to swim the Mozambique Channel? (c) How valid is the Ali‐Huber model predicting that eastward Palaeogene surface currents allowed rafts to reach Madagascar in 3–4 weeks? Finally, we explored the alternative hypothesis of geodispersal via short‐lived land bridges between Africa and Madagascar.LocationEast Africa, Madagascar, Mozambique Channel.TaxaFish, amphibians, reptiles, birds, mammals.MethodsWe established colonization timeframes using molecular divergence dates estimated for Malagasy vertebrate lineages. We reviewed the likelihood of the “torpid waif” and “swim...

Geophones are essential for monitoring seismic activity to study the structure of the earth for g... more Geophones are essential for monitoring seismic activity to study the structure of the earth for ground surveys, mineral exploration and early warning detection of geo-hazards. Traditional electromagnetic based geophones are fairly effective in detecting micro-seismic activity and ambient signals. Their induction based mass-spring sensing mechanism can however be somewhat performance limiting. Limitations include reduced frequency response, resolution and recovery times between successive activities. This ultimately impacts the sensitivity and performance of the device. In this paper, we present a novel optical fiber geophone sensor that addresses these issues through superior sensitivity, performance and ease of deployment. Our optical fiber geophone is polarization based, single ended and operates on a Michelson interferometric principle. Tests were performed to compare the performance of our optical fibre geophone to that of a commercial electromagnetic geophone. Vibrations of varying magnitude were remotely generated at 1.065 m from both devices. Sensor signal responses to disturbances of energy lower than 1.1 mJ were plotted and analysed. Observed traces from the sensor responses were compared, showing that the fiber geophone has significantly shorter response and recovery times. As a result, the resolution between rapidly succeeding signals is considerably greater for the optical fiber geophone. Sensitivity plots of the amplitude response to the vibration energy gave a scatter of points depicting a higher degree of precision and accuracy for the fiber geophone. Response slopes of 11.70 a.u/mJ and 10.31 a.u/mJ respectively were obtained for the sensitivity of the optical fiber geophone versus the electromagnetic geophone. While the typical spurious frequency is close to 150 Hz for the traditional geophone, the bandwidth of the optical fiber geophone is an order of magnitude greater.

Proceedings of the Adaptive Optics for Extremely Large Telescopes 5, 2017

After the development of the OCAM2 EMCCD fast visible camera [1] dedicated to advanced adaptive o... more After the development of the OCAM2 EMCCD fast visible camera [1] dedicated to advanced adaptive optics wavefront sensing, First Light Imaging moved to the SWIR fast cameras with the development of the C-RED One and the C-RED 2 cameras. First Light Imaging's C-RED One infrared camera is capable of capturing up to 3500 full frames per second with a subelectron readout noise and very low background. C-RED One is based on the last version of the SAPHIRA detector developed by Leonardo UK. This breakthrough has been made possible thanks to the use of an e-APD infrared focal plane array which is a real disruptive technology in imagery. C-RED One is an autonomous system with an integrated cooling system and a vacuum regeneration system. It operates its sensor with a wide variety of read out techniques and processes video on-board thanks to an FPGA. We will show its performances and expose its main features. In addition to this project, First Light Imaging developed an InGaAs 640x512 fast camera with unprecedented performances in terms of noise, dark and readout speed based on the SNAKE SWIR detector from Sofradir. The camera was called C-RED 2. The C-RED 2 characteristics and performances will be described. The project leading to this application has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement N° 673944. C-RED2 development is supported by the "Investments for the future" program and the Provence Alpes Côte d'Azur Region, in the frame of the CPER.

International Kimberlite Conference Extended Abstracts: 2008

Extreme Natural Events, 2022

Advances in Geophysics, Tectonics and Petroleum Geosciences

3rd SAGA Biennial Conference and Exhibition, 1993

Le Centre pour la Communication Scientifique Directe - HAL - Université de Bretagne Occidentale, Nov 1, 2021

$Research paper thumbnail of Geohazard components of Strategic Environmental Assessments in South Africa: fracking, electricity grid infrastructure & gas pipeline networks$

Journal of the Optical Society of America B, 2020

An interferometric fiber sensor was developed and used to detect polarization changes resulting f... more An interferometric fiber sensor was developed and used to detect polarization changes resulting from varying the amplitude and frequency of an acoustic signal. The sensor was designed to be suited to geological activities such as seismic tomography, detection of sink holes, and early warning earthquake detection. The fiber sensor and a commercial geophone were subjected to the same tests to compare their characteristic response to different vibrations. The average signal sensitivities were 9.15 a.u./mJ and 8.37 a.u./mJ for the fiber sensor and geophone, respectively. The ability of each sensor to distinguish between short, successive events showed that the fiber sensor has superior sensitivity and resolution. This is attributed to the short recovery time of the optical fiber sensor. The geophone is limited in this regard by its inherent Faraday magnet and coil damping mechanism. The bandwidth of the optical fiber sensor is shown to be 3.349 kHz, more than 20 times that of the commer...

South African Journal of Geology, 2001

Quick Search: All GSW Journals, GSW + GeoRef. advanced search. ...

Journal of African Earth Sciences, 1994

The 2-D spectral analysis of gravity and topography data has been used to identify structural tre... more The 2-D spectral analysis of gravity and topography data has been used to identify structural trends of recognized geological entities within the tectonic provinces of South Africa. The mean amplitude of the spectra within very thin rings, taken to have the same mean wavenumber, is subtracted from the total spectrum to give the non-isotropic component. This component of the spectrum reflects more of the heterogeneity of the data and is exploited to produce trends. These results are consistent with known structural trends, but also reveal new trends. Some trends, identified on the Kaapvaal craton using gravity data, are at variance with those obtained from the topography. This suggests that in this area crustal mass distribution is not correlated with surface relief. No dominant structural trend was identified in the Witwatersrand basin. It can be concluded from these findings that this technique can be successfully applied to various data sets, which reflect different physical properties and hence assist in geological interpretation, regardless of the scale. R4sum4-L'analyse spectrale 2-D de donnres de gravit6 et de topographie est utilisre pour identifier des linraments structuraux d'entitrs grologiques connues dans les provinces tectoniques d'Afrique du Sud. Les composantes anisotropes du spectre, qui refl~tent l'hrt4rog4nrit6 des donn4es, sont utilis4es. Les r4sultats confirment les linraments structuraux connus et en rrvrlent de nouveaux. Certains linraments identifirs sur le craton du Kaapvaal a partir de la gravit6 different de ceux reconnus/l partir de la topographie. Ceci suggrre que la distribution de la masse crustale n'est pas corrdlre avec le relieL Sur base de ces rrsultats, on peut conclure que cette technique peut ~tre appliqures avec succrs sur des ensembles de donnres reflrtant des proprirt4s physiques diffrrentes et ainsi aider ~ l'interprrtation grologique, quelle que soit l'rchelle considrr4e.