Probabilistic seismic hazard analysis for Northern Tanzania Divergence Region and the adjoining areas

This paper presents the seismic hazard levels for the Northern Tanzania Divergence (NTD) and adjoining areas by using area seismic source zones. The 15 source zones were considered based on the major geological and tectonic features, faulting style, and seismicity trends. For each source, earthquake recurrence parameters were computed by using the earthquake catalogue with events compiled from 1956 to 2011. The peak ground accelerations (PGA) and spectral accelerations (SA) at 0.2 and 2.0 second, respectively, were computed for a 10% probability of exceedance in 50 years at sites defined by a 0.1° x 0.1° grid. The recurrence parameters of 15 zones and attenuation relations developed by Akkar et al. (2014) and Chiou and Youngs (2014) were integrated in a logic tree. Obtained results that are presented as hazard maps show strong spatial variations ranging from 60 to 330 cm/s/s for PGA, from 100 to 650 cm/s/s at 0.2 sec and from 6 to 27 cm/s/s at 2 sec for 475 years mean return period and 5% damping. Hazard levels depict the general tectonic setting of the study area with the western (Eyasi-Wembere) and central (Natron-Manyara-Balangida) rift segments having relatively high PGA values compared with the eastern Pangani rift. This work provides indications of seismic hazards to policymakers and planners during planning and guidelines for earthquake-resistant design engineers. Keywords: Homogeneous Earthquakes Catalogue; GMPE; PSHA; NTD