Statistical evaluation of seismic event location accuracy by the South African National Seismograph Network over four decades

We analyzed the changes/improvements of seismic event detection and location accuracy of the South African National Seismograph Network over the last four decades. The effect of three regional velocity models on epicentral solutions was tested during the initial study. It is shown that the hypocentral depth considered during this study, viz. at 2 km for mining related events, and 5 km to 10 km for tectonic earthquakes, have a negligible effect on the error in epicentre location. Further, three detection distances were evaluated during this study, viz. 300, 500 and 1000 km. The location errors decreased significantly by increasing the detecting distance. This study highlights the importance of including 5-phase arrival times to better constrain seismic event locations. This observation is of particular value for the 1970 to 1997 period, when only P-phases were considered during the location procedure. Lastly, it is shown how the errors in epicentre location decrease with an increase in the number and geographical distribution of seismic stations.The South African National Seismograph Network operated by the Geophysics Competency of the Council for Geoscience.http://sajg.geoscienceworld.orgam2017Geolog

Investigation of an octagon-shaped chimney solar power plant

South Africa has limited reserve electricity resources and many parts of the country have limited access to electricity, while electricity production capacity is at maximum and almost every gigawatt is accounted for. The energy crisis has highlighted the need to increase electricity generation capacity and to search for alternative energy sources. This study focuses on the solar chimney concept, which harnesses both solar and wind energy to generate electricity, especially in the sunny Northern Cape Province and Karoo regions of South Africa. The concept is an alternative design focusing on very low wind power, where an effective cone solar frustum power plant is able to generate sufficient wind flow to turn a turbine and produce electricity. The study focused on different chimney designs (cylindrical and octagon shapes) to evaluate the best performance. Simulations were performed to find the optimum design configuration to focus the research. The simulations evaluated the shape of the tower, tower base, heat transfer surface areas and efficiencies of the system. The results showed that the octagonal chimney outperformed the normal cylindrical one, mainly due to an increased airflow and the turbine being positioned at the outlet of the chimney (whereas it is at the bottom of a cylindrical chimney). The addition of mirrors increased the performance due to solar radiation from all the directions around the chimney. The results were confirmed by a pilot plant that was operated continuously for 24 months

Comparison and quantitative study of vulnerability/damage curves in South Africa

Southern Africa is considered a stable continental region in spite of several reported medium size earthquakes, some of which caused considerable damage and casualties. The 1969 Ceres 6.3 magnitude earthquake is considered the most destructive and caused serious damage estimated at US$24 million, with 12 mortalities and many more injured. Others include six mining related tremors which caused significant damage i.e. Welkom 1976, Klerksdorp 1977, Welkom 1989 and Carletonville 1992 seismic events. Notable for their damage to infrastructure was the 9th March 2005 Stilfontein event near Klerksdorp and 5th August 2014 event near Orkney. Most buildings and structures in South Africa are not designed to resist even relatively low intensity earthquake. Most architects, engineers and builders in South Africa do not consider seismic resistance as a design requirement. In this work, potential damage caused by strong earthquake was estimated for three classes of buildings situated in Sandton, Cape Town, Durban and Port Elizabeth. The effect of earthquakes causing damage was studied by considering the “worst case-scenario”, i.e. the occurrence of an earthquake with the maximum possible magnitude for an area. In four studied urban areas, expected damage was estimated for three classes of buildings: unreinforced masonry, bearing wall, low rise, reinforced concrete shear wall, without moment resisting frame, medium rise, and reinforced concrete shear wall, without moment resisting frame, high rise. The results of the analysis showed that in case of occurrence of a strong earthquake, the most damage is expected for the building classified as ‘unreinforced masonry, bearing wall, low rise, and reinforced concrete shear wall’.http://sajg.geoscienceworld.org/am2016Geolog

Area selection for diamonds using magnetotellurics : examples from southern Africa

Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Lithos 112 (2009): 83-92, doi:10.1016/j.lithos.2009.06.011.Southern Africa, particularly the Kaapvaal Craton, is one of the world’s best natural laboratories for studying the lithospheric mantle given the wealth of xenolith and seismic data that exist for it. The Southern African Magnetotelluric Experiment (SAMTEX) was launched to complement these databases and provide further constraints on physical parameters and conditions by obtaining information about electrical conductivity variations laterally and with depth. Initially it was planned to acquire magnetotelluric data on profiles spatially coincident with the Kaapvaal Seismic Experiment, however with the addition of seven more partners to the original four through the course of the experiment, SAMTEX was enlarged from two to four phases of acquisition, and extended to cover much of Botswana and Namibia. The complete SAMTEX dataset now comprises MT data from over 675 distinct locations in an area of over one million square kilometres, making SAMTEX the largest regional-scale MT experiment conducted to date. Preliminary images of electrical resistivity and electrical resistivity anisotropy at 100 km and 200 km, constructed through approximate one-dimensional methods, map resistive regions spatially correlated with the Kaapvaal, Zimbabwe and Angola Cratons, and more conductive regions spatially associated with the neighbouring mobile belts and the Rehoboth Terrain. Known diamondiferous kimberlites occur primarily on the boundaries between the resistive or isotropic regions and conductive or anisotropic regions. Comparisons between the resistivity image maps and seismic velocities from models constructed through surface wave and body wave tomography show spatial correlations between high velocity regions that are resistive, and low velocity regions that are conductive. In particular, the electrical resistivity of the sub-continental lithospheric mantle of the Kaapvaal Craton is determined by its bulk parameters, so is controlled by a bulk matrix property, namely temperature, and to a lesser degree by iron content and composition, and is not controlled by contributions from interconnected conducting minor phases, such as graphite, sulphides, iron oxides, hydrous minerals, etc. This makes quantitative correlations between velocity and resistivity valid, and a robust regression between the two gives an approximate relationship of Vs [m/s] = 0.045*log(resistivity [ohm.m]).We especially thank our academic funding sponsors; the Continental Dynamics programme of the U.S. National Science Foundation, the South African Department of Science and Technology, and Science Foundation Ireland

The perceived influence of diversity factors on effective strategy implementation in a higher education institution

Managing diversity is one of the major challenges in higher education institutions in South Africa. Additionally, effective strategy implementation is vital for an institution to be successful and sustainable. Questionnaires were distributed to the management of Walter Sisulu University, South Africa, to investigate the relationship between diversity factors and effective strategy implementation. The questionnaires interrogated the effect of the acculturation process, the degree of structural integration, the degree of informal integration, institutional bias and intergroup conflict, and how these factors influence strategy implementation. Structural equation modelling (SEM) was employed as the statistical tool to confirm the hypothetical model. Results of this study revealed that there is no statistically significant relationship between diversity and strategy implementation at the institution, and imply that diversity among staff do not impact on the successful achievement of strategic objectives in the institution. The findings of the study are contrary to empirical evidence by other studies

Statistical evaluation of seismic event location accuracy by the South African National Seismograph Network over four decades

We analyzed the changes/improvements of seismic event detection and location accuracy of the South African National Seismograph Network over the last four decades. The effect of three regional velocity models on epicentral solutions was tested during the initial study. It is shown that the hypocentral depth considered during this study, viz. at 2 km for mining related events, and 5 km to 10 km for tectonic earthquakes, have a negligible effect on the error in epicentre location. Further, three detection distances were evaluated during this study, viz. 300, 500 and 1000 km. The location errors decreased significantly by increasing the detecting distance. This study highlights the importance of including 5-phase arrival times to better constrain seismic event locations. This observation is of particular value for the 1970 to 1997 period, when only P-phases were considered during the location procedure. Lastly, it is shown how the errors in epicentre location decrease with an increase in the number and geographical distribution of seismic stations.The South African National Seismograph Network operated by the Geophysics Competency of the Council for Geoscience.http://sajg.geoscienceworld.orgam2017Geolog

Foundation requirements for a lunar laser ranger facility at matjiesfontein, South Africa

This paper addresses foundation requirements to construct a new Geodetic/Geophysical Observatory at approximately five kilometers south of Matjiesfontein, in the southwestern Karoo. The observatory will host a Lunar Laser Ranger, Satellite Laser Ranger, and other collocated geophysical instruments, such as seismic and gravimeter stations, to be located in a specially designed vault. Field and laboratory tests and surveys show that the site is stable and capable of supporting the 5 ton weight of the Lunar Laser Ranger (LLR) structure that includes a one meter diameter optical telescope and mount to conduct laser-ranging experiments. The foundation requirements for auxiliary buildings and calibrating beacons required for the instrument and the envisaged experiments wt re also included in this study. © 2011 December Geological Society of South Africa

Geotechnical investigation for the construction of a vault in a rockface for the placement of a gravimeter and a long period seismograph at matjiesfontein, South Africa

The aim of the project is to investigate the rock mass parameters at a site in the vicinity of Matjiesfontein (Western Cape Province) so as to ascertain the suitability for the construction of a vault in a rock face. This vault will host a permanent LaCoste and Romberg ultrasensitive gravimeter as well as a long period seismograph. The site is close to the contact between the Dwyka Formation of the Karoo Supergroup and the Witteberg Group, both part of the Cape Supergroup. A site survey, joint analysis, core logging and laboratory testing on rock specimens formed part of the geotechnical investigation. Laboratory tests included unconfined compression strength and point load tests. The data obtained from the fieldwork and laboratory analysis were used to determine the rock quality designation value of the rock, which was subsequently combined with the other parameters to obtain a rock mass rating. All data were utilised to develop a model for best practice construction (e.g. excavated vault in solid rock versus a concrete structure against rock face), as well as to develop a preliminary design for the vault. The results of the geotechnical investigation indicate that the site is suitable for the proposed project. © 2011 December Geological Society of South Africa

A new geodetic research data management system at the Hartebeesthoek Radio Astronomy Observatory

<p>The Hartebeesthoek Radio Astronomy Observatory (HartRAO) hosts two research programmes: radio astronomy and space geodesy. The Space Geodesy programme has four main co-located space geodetic techniques, making HartRAO a true fiducial site. These techniques are Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), geodetic Very Long Baseline Interferometry (VLBI) and Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS). Only GNSS data are stored on-site in a publicly accessible repository. The <em>HartRAO</em> <em>Space Geodesy Programme</em> is expanding its geodetic techniques with Lunar Laser Ranging (LLR) as well as a network of seismometers, accelerometers, tidal gauges and gravimeters. These instruments will be installed across the southern African region and will generate large volumes of data that will be streamed to and stored at HartRAO.</p> <p>Our objective is to implement a complete <em>Geodetic Research Data Management System (GRDMS)</em> to handle all HartRAO’s geodetic data on-site in terms of archiving, indexing, processing and extraction. These datasets and subsequent data products will be accessible to both the scientific community and general public through an intuitive and easy to use web-based frontend. As the first step in this process, we are currently working on establishing a new data centre. This opens up the possibility for the librarian to provide data services and support by working together with researchers and information technology staff.</p> <p>We discuss the rationale, role players and top-level system design of this GRDMS, as well as the current status and planned products thereof.</p