Investigations on the seismicity of Kenya using the university of Nairobi seismic network

Abstract

The University of Nairobi has had a seismological network since 1963 as part of the WorldWide Standardized Seismic Network (WWSSN). Later, in the 1990's, other stations were installed in Kenya at different times. In this study, data from five digital stations and one broadband station have been used for the period November 1999 to December 2001. The performance of the stations has been checked and found to be relatively good, yielding 3000 detected events for that period. After thorough analysis, 526 well-located events were selected of which 306,202 and 18 were local, regional and teleseismic, events respectively. Data from the Eastern and Southern African Regional Seismological Working Group (ESARSWG) have been used to constrain the locations. Usually prompt event locations reports that have been provided previously during the said period utilized single station data and are associated with high location errors, because they do not take into account all the available data from the other remotely located stations in the country. This study has synthesized all the available seismic data for this period to generate more precise and constrained event locations. Seismic patterns and trends, not realized before and not related to any known active faults are revealed. Computed seismic energy maps and other results have been used to characterize the subsurface and classify certain regions as possible earthquake risk zones. The study classifies the regions into four zones according to the seismicity, geological, and geographical settings. The four zones are the southern Kenya rifts, southeast Kenya, Central rift and Mt Kenya regions