SPECIAL VOLUME

R.J. DURRHEIM

A.A. NYBLADE

P.H.G.M. DIRKS

IntroductionWith support from many public and privateorganisations, AfricaArray has become a multi-facetedinitiative, promoting a broad range of educational andresearch activities. Thirty M.Sc. and Ph.D. students havebeen supported since 2005 at five partneringuniversities, and over 40 students have completed B.Sc.honours degrees at the University of the Witwatersrand.A network of more than 30 permanent broadbandseismic stations spread across eastern, southern andwestern Africa has been created to provide data for newprojects, several project-specific temporary deploymentsof seismic stations have been conducted, and an annualinternational geophysics field course has beenestablished.

This special volume includes mostly papers that werepresented at the 4th annual AfricaArray workshop held17–18 June, 2008 at the University of the Witwatersrand,Johannesburg, and its main purpose is to assemble inone place the scientific results from many of the firstM.Sc. and Ph.D. students and postdocs supported byAfricaArray (Dugda et al., Hansen et al., Mavonga andDurrheim, Mulibo and Nyblade, Tugume and Nyblade).Because most of the students and postdocs supportedby AfricaArray have completed research projects inearthquake seismology, and because all but two of theother papers in this volume are in seismology, by defaultthe general theme of this special volume is earthquakeseismology.

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AfricaArray SPECIAL VOLUME

INTRODUCTION

R.J. DURRHEIMUniversity of the Witwatersrand, Private Bag 3, WITS, 2050 South Africa CSIR, South Africae-mail: rdurrhei@csir.co.za

A.A. NYBLADEDepartment of Geosciences, Pennsylvania State University, University Park, Pennsylvania,United States of Americae-mail: andy@geosc.psu.edu

P.H.G.M. DIRKSSchool of Geosciences, University of the Witwatersrand, Private Bag 3, Johannesburg, 2050, South AfricaCurrent Address: School of Earth and Environmental Science, James Cook University, Townsville, Qld 4811, AustraliaCorresponding author: e-mail: paul.dirks@jcu.edu.au

© 2009 December Geological Society of South Africa

AfricaArray (www.AfricaArray.org) is a 20-year initiative, started in 2005, to meet the New Partnership for Africa’s

Development (NEPAD) requirements for continent-wide cooperation in human resources development and science capacity

building. The name “AfricaArray” refers to arrays of scientists working on linked projects across the continent; arrays of shared

training programmes and observational networks; and above all, a shared vision that Africa will build and retain capacity in an

array of technical and scientific fields. AfricaArray was established through a partnership of three organisations, the University of

the Witwatersrand (Johannesburg, South Africa), the Council for Geoscience (Pretoria, South Africa), and the Pennsylvania State

University (University Park, PA, United States of America), to address demands for a well-trained geosciences workforce in

Africa by industry, government, and academia. For details about AfricaArray, the reader is referred to Dirks (2006), Nyblade et al.

(2008), and Durrheim (2008).

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The papers can be divided into two categories, thosethat investigate Earth structure and those focused onseismicity and seismic hazards. Four of the papers thatinvestigate Earth structure use receiver functions, eitherby themselves (Gore et al., Hansen et al.) or incombination with other seismic data (Dugda et al., Kimet al.). Gore et al. analyse P-wave receiver functionsrecorded by the Southern African Seismic Experiment toimage crustal and uppermost mantle structure beneaththe Zimbabwe Craton and Limpopo Belt. Hansen et al.analyse S-wave receiver functions from ten permanentseismic stations in southern, central and eastern Africathat have been in operation for many years to estimatethe thickness of both the crust and lithosphere. Dugda et al. combine P-wave receiver functionsandsurface wave group velocities to model the S-wavevelocity structure of the crust and uppermost mantlebeneath Kenya, and compare their results to similarmodels available for other parts of the East AfricanPlateau, as well as the Ethiopian Plateau. Kim et al. alsouse receiver functions to investigate crustal structurebeneath the Rukwa rift in southern Tanzania, andcomplement the receiver functions by modellingregional seismograms from a magnitude 5.9 earthquakerecorded on a seismic station at the south eastern end ofthe rift.

Three papers examine other aspects of Earth Structure.Tugume and Nyblade use the depth distribution ofseismicity at the northern end of the RwenzoriMountains in Uganda to estimate heat flow from thatregion within the Western Branch of the East African RiftSystem. Greenstone belts are investigated in two studies:Gwavava and Ranganai use aeromagnetic and gravitydata to investigate the subsurface structure of theMasvingo Greenstone Belt in the Zimbabwe Craton,while Dirks et al. conduct kinematic analysis offractures to infer the tectonic processes that governedArchaean gold mineralisation in the BarbertonGreenstone Belt in the Kaapvaal Craton.

The ensemble of these papers attest to the wide rangeof geophysical and geological research on African Earthstructure that is being undertaken by AfricaArraystudents and postdocs, as well as by faculty associatedwith AfricaArray, and together represent a significantadvancement in our understanding of the structure andtectonics of the African plate.

The second category of papers can in turn be dividedinto two groups, one group focusing on seismic andtsunami hazards, and the other more generally onseismicity. In two papers, one by Amponsah et al. andthe other by Mavonga and Durrheim, seismic hazardassessments are made for two areas. Amponsah et al.model seismic ground motion in the greater Accrametropolitan area in Ghana to better understand peakground acceleration and velocity that can be expectedfrom local and regional earthquakes. Mavonga and

Durrheim use a probabilistic approach to map theseismic hazard in the Democratic Republic of Congo andsurrounding areas, and assess the seismic hazard levelfor 14 cities in the region of study.

Two papers, Okal et al. and Okal and Hartnady,examine tsunami hazard along the eastern and westerncoastlines of Africa. In Okal et al., new run-up data inthe Comoro Islands and Tanzania from the 2004 Sumatraearthquake are reported and used to assess the regionaltsunami hazard from future Sumatra earthquakes. Okal and Hartnady, on the other hand, useseismological data from the 27 June 1929 magnitude 8South Sandwich Islands earthquake to investigate thetsunami risk associated with such large earthquakes forthe South Atlantic basin.

The other papers with a focus on seismicity are morewide-ranging. Julia et al. introduce a procedure basedon Wadati diagrams to assess and improve theconsistency of P- and S-wave travel time picks for smallmine-induced seismicity from deep gold mines in SouthAfrica. Shumba et al. present a focal mechanism for the15 March 2008 Nyamandlovu earthquake in Zimbabweand link its origin to pore pressure changes in asandstone aquifer. Mulibo and Nyblade investigateseismicity in two earthquake swarms in northernTanzania to determine the depth distribution of theevents and to ascertain the cause of the swarms. Similarto the papers on Earth structure, the papers that fallwithin the seismicity/hazard category reflect the breadthof science that has been enabled by AfricaArray.

As guest editors of the AfricaArray Special Volume, wewould like to thank all the referees (see list below) andauthors helping to make this publication possible, and inparticular Jay Barton for his editorial guidance. We triedto ensure that each paper was reviewed by at least oneAfrican and one international reviewer. We would alsolike to thank all of the many partners and supporters ofAfricaArray for their generous contributions and forsharing in the vision that Africa must build and retaincapacity in an array of technical and scientific fields tosecure its future development and growth.

We sincerely thank the following referees: CarlAnhaeusser (University of the Witwatersrand, SouthAfrica), Atalay Ayele (Univeristy of Addis Ababa,Ethiopia), Ian Bastow (University of Bristol, UnitedKingdom), Tom Blenkinsop (James Cook University,Australia), Jose Borrero (University of SouthernCalifornia, United States of America), Artur Cichowicz(Council for Geoscience, South Africa), Johan de Beer(South Africa), Damien Delvaux (Royal Museum forCentral Africa, Belgium), Richard Ferdinand (Universityof Dar es Salaam, Tanzania), Cindy Ebinger (Universityof Rochester, United States of America), StewartFishwick (University of Leicester, United Kingdom),Dumisani Hlatywayo (National University of Science and

Technology, Zimbabwe), Mike Jones (University of theWitwatersrand, South Africa), Jordi Julià (PennsylvaniaState University, United States of America), KatieKeranen (University of Oklahoma, United States ofAmerica), Andrzej Kijko (University of Pretoria, SouthAfrica), Geoffrey King (Institut de Physique du GlobeParis, France), Jan Kramers (University of Berne,Switzerland), Andrew King (CSIRO, Australia), LindsayLinzer (Meerkat cc, South Africa), Rocco Malservisi(Ludwig-Maximilians University, Germany), MartinMushayandebvu (Image Interpretation TechnologiesInc., Canada), Teresia Nguuri-Francis (United Kingdom),Vungani Midzi (Council for Geoscience, South Africa),

Colin Reeves (Earthworks, The Netherlands), KenjiSatake (University of Tokyo, Japan), Graham Stuart(University of Leeds, United Kingdom), Shariar Talebi(CANMET, Canada), Herbert Uzoegbo (University of theWitwatersrand, South Africa), Richard Wonnacott(Department of Land Affairs, South Africa).

References

Dirks, P.G.H.M., (2006). AfricaArray: Building a Scientific Workforce for

Africa’s Natural Resources Sector, Traders African Business Journal,

25, 54–55.

Durrheim, R. (2008). AfricaArray, Quest, 4, 14–15.

Nyblade, A., P. Dirks, R. Durrheim, S. Webb, M. Jones, G. Cooper, G.

Graham, (2008) AfricaArray: Developing a Geosciences Workforce for

Africa’s Natural Resource Sector, The Leading Edge, 27, 1358–1361.

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