Recent Developments in the Definition of Design Earthquake Ground Motions Calling for a Revision of the Current Ethiopian Seismic Code - EBCS 8: 1995

Recent developments in the definition of design ground motions for seismic analysis of structures are presented. A summary of results of empirical and analytical site-effect studies are provided and recent findings from empirical studies on instrumental records are compared against similar results from earlier studies. Pertinent changes introduced in recent editions of international codes as a result of these evidences are presented. Comparisons of relevant provisions of EBCS 8: 1995 with those in contemporary American, European and South African codes are made. The paper presents compelling evidences showing that the amplification potential of site-soils can in general be significantly larger at sites of lowamplitude rock-surface acceleration up to 0.1g than at sites of larger accelerations. Noting the practical significance of this fact on the seismic design of structures in low to moderate seismic regions, to which many cities and towns of Ethiopia belong, changes to selected provisions of the local code are proposed. KEY WORDS: Earthquake ground motion, return period, response spectra, seismic hazard, site amplification.