Seismicity in East Africa: A statistical analysis

Abstract

In this thesis, we present a statistical analysis of the seismicity along the East African Rift. We also distinguished the different branches of the rift: the Eastern branch (EB), the Western branch (WB), the Main Ethiopian rift (MER) and the Southeastern branch (SEB). We used QGIS to generate the maps showing the seismicity distribution in all above segments. We systematically analyzed, both in the entire region and in the different branches, the distribution of the seismicity as a function of time, depth, magnitude, latitude and longitude. To do so, we built a home-made Python script. We generated simple and bi-variate histograms, and calculated statistical quantities such as the mean, standard deviation, skewness and kurtosis. Furthermore, we calculated the length of each branch using a on-line tool. Our results show the presence of 1) a deep seismic activity (33km) particularly in the WB, 2) a seismic crisis in 2005 in MER, 3) a migration of the seismic activity towards the south in the last ten years and 4) a trend for a shallower activity along the entire rift since 2010. We also find that the distinction between different branches further highlighted the dominant seismic activity in the MER and WB region which contrasted with the EB and SEB branches. Our findings have implications for the yield stress envelopes in the region and the correlation between the volcanic and seismic activity along the rift. They also suggest an influence of the sub-lithospheric flow of Afar mantle plume material on the seismicity along the rift