Assessing seismic hazard of the East African Rift: a pilot study from GEM and AfricaArray
Valerio Poggi, Raymond Durrheim, Georges Mavonga Tuluka, Graeme Weatherill, Robin Gee, Marco Pagani, Andrew Nyblade, Damien Delvaux
The East African Rift System is the major active tectonic feature of the Sub-Saharan Africa region. Although the seismicity level of this divergent plate boundary can be described as moderate, several damaging earthquakes have been reported in historical times, and the seismic risk is exacerbated by the high vulnerability of the local buildings and structures. Formulation and enforcement of national seismic codes is therefore an essential future risk mitigation strategy. Nonetheless, a reliable risk assessment cannot be done without the calibration of an updated seismic hazard model for the region. A major limitation affecting the assessment of seismic hazard in Sub-Saharan Africa is the lack of basic information needed to construct source and ground motion models. The historical earthquake record is sparse, with significant variation in completeness over time across different regions. The instrumental catalogue is complete down to sufficient magnitude only for a relatively short time span. In addition, mapping of seismogenically active faults is still an on-going task, and few faults in the region are sufficiently constrained as to allow them to be directly represented within the seismic hazard model. Recent studies have identified major seismogenic lineaments, but there is substantial lack of kinematic information for intermediate-to-small scale tectonic features, information that is essential for the proper calibration of earthquake recurrence models. In this study, we use new data and Global Earthquake Model (GEM) computational tools such as the Hazard Modeller’s Toolkit and the OpenQuake engine to perform a pilot study of the seismic hazard associated with the East African Rift. The hazard model obtained has been created using the most recent information available from scientific literature, global bulletins and local earthquake catalogues, including those from AfricaArray projects. In this report, in accordance with the GEM philosophy, we describe in detail all working assumptions, main processing steps, data analyses and interpretations used for the model setup.