04.12.2018 - UNESCO Office in Nairobi

A platform for the Seismic Hazard Evaluation in the East African Rift System

Seismotectonics of the north and central regions of the East African Rifts (c)UNESCO

The International Geoscience Programme (GCP) Working Group met in Dar Es Salaam, Tanzania, to discuss the possibility of integrating the Global Monitoring of Environment and Security (GMES) programme in the frame of the African Union and European Union agreement.

For the seismic hazard assessment, the seismotectonic characteristics of the Kenya and Ethiopia sections of the East African Rift System rely on the 3 – 5 mm/yr rates of active deformation and on the seismogenic structures previously identified in the Seismotectonic Map of Africa (IGCP-601 project; Meghraoui et al., 2016). Among characteristic earthquakes with surface ruptures, a study was conducted on the seismic source parameters of the 25 August 1906 earthquake (Mw 6.5) near Ginir, and the 6 January 1928 Subukia valley earthquake (Mw 7.0; Ambraseys, 1991; Ayele and Kulhanek, 2000). The previous Global Seismic Hazard Assessment Program (GSHAP) model, including part of the African region, was based upon classical probabilistic seismic hazard assessment (PSHA) principles (Giardini et al., 1999). 

Recently, conventional PSHA has come under serious criticism for evident failures of sound evaluations (Stein et al., 2012; Kossobokov and Nekrasova, 2012; Wyss et al., 2012). In current case the working group tested the application of a scenario-based deterministic and PSHA approach applied to the East African Rift System (EARS; Ksentini & Romdhane, 2014). Although the earthquake recurrence period for large earthquakes (with Mw > 6.5) is poorly known for the study area, the International Geoscience Programme (GCP) Working Group observed that the occurrence of a 1928 earthquake size at ~150 km distance from the recently grown Nairobi urban region would generate 0.3 to 0.4g ground acceleration.

For this reason, the GCP Working Group met in Dar Es Salaam, from 8 to 10 October 2018, to discuss the possibility of integrating the Global Monitoring of Environment and Security (GMES) programme, in the framework of the African Union and the European Union agreement. The GMES information was launched in July 2018 and the Working Group looks forward for a call in order to submit the SEISMOSHAF proposal.

The constitution of a robust database is the main component for the Deterministic Hybrid Seismic Hazard Assessment (DHA) and Probabilistic Hybrid Seismic Hazard Assessment (PSHA). Six topics were addressed, concerning the Earthquake catalogue compilation and updating, analysis and homogenization, the Morphotectonic / remote-sensing data compilation and analysis, the Compilation of active-fault database and seismic source characteristics, the compilation and updating of geodetic data for study region, the compilation of crustal structure models and the attenuation relationships and Ground Motion Prediction Equations.

The Working Group considered the work programme of PhD students (e.g., the contribution of Sophie Kipkwony) as a priority in the objectives of the IGCP-659 programmes. The proposed work will have to concentrate on seismic microzonation hazard studies within the capital cities of Nairobi (Kenya) and Addis Ababa (Ethiopia). The programme aims at studying the seismic source characteristics, local site effects (seismic ground response), subsurface characterization, seismic hazard and risk analysis (SHA and SRA). These three main aspects will be investigated with the aim of generating a seismic microzonation map of the capital cities. During the working group meeting almost 14 experts presented various research finding related to seismic activities in East African rift and adjacent areas.

The research topic is timely and will have an immense contribution to the safety of the East African community. There is a very good potential of human resources in the region who are capable of producing high level science results in collaboration with the African and international experts pool. Involving postgraduate students (PhDs and MSc) and young researchers will have tremendous contributions.

The meeting and discussions carried out gave the group the momentum to get better organized as a SHA-SRA Working Group in order to conduct in depth investigations on the subject in question. 

As recommendation, discussions on retreat meetings of selected experts were tackled, for a period of two weeks to one month. With a prior preparation, the Working Group will be able to provide sound scientific reports on the status of the SHA - SRA and impact on the society of major cities in Africa.

The working group coordinated by Prof Mustapha Meghraoui from Institut de Physique du Globe, CNRS-UMR 7516, University of Strasbourg, France, and Algerian Academy of Science and Technology.

 




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