Probabilistic seismic hazard analysis for the northern Tanzania divergence

This thesis presents the results of the research work done over Northern Tanzania Divergence (NTD) and adjoining areas bounded by 2oS to 7oS and 34oE to 40oE. A working catalogue of main shocks was prepared by compiling earthquake events (since 1956 to 2011) from various data sources; ranging from the National/Local, Regional and International catalogues and/or bulletins. The compilation of the composite catalogue involved merging them into a single database; then followed by removing duplicates, foreshocks, aftershocks and those earthquakes listed without any magnitude estimate. The final compiled catalogue was then homogenized into moment magnitude, Mw. The homogenized catalogue was declustered before embarking into recurrence parameters computation for each seismic source zone. The catalogue compilation was followed by the seismic source characterization and zonation which led into delineating fifteen potential areal seismic source zones based on the major geological and tectonic features, faulting style and seismicity trends within NTD. The attenuation relations developed by Akkar et al. (2014) and Chiou and Youngs (2008) were used by employing logic tree approach. The Peak Ground Accelerations (PGA) and spectral accelerations at structural ordinates 0.2 second and 2.0 seconds, respectively, were computed for 10% probability of exceedance (i.e., 90% chance of non-exceedance) in 50 years, at sites defined by a grid of 0.1o X 0.1o. The PGA values over the grid points were contoured to obtain a seismic hazard map. The hazard map depicts that the western and central rift segments have relatively high PGA and spectral accelerations. The maximum PGA observed within NTD is 309.9 cm/s/s, whereas, the maximum spectral accelerations at T = 0.2 seconds and T = 2.0 seconds, are 631.7 cm/s/s and 26.4 cm/s/s, respectively. The areas with high hazard levels are the ones with high observed seismic activities and large magnitudes within NTD. The contoured hazard maps will allow policy makers and planners to get indications of the hazard levels in the site before planning. This thesis provides engineers with guidelines for earthquake resistant design. The seismic hazard results produced are key input parameters into the assessment of seismic risk, which yields probabilistic estimates of the expected loss of property and lives from earthquakes.