A review on the multi-criteria seismic hazard analysis of Ethiopia: with implications of infrastructural development

Abstract

Earthquake is a sudden release of energy due to faults. Natural calamities like earthquakes can neither be predicted nor prevented. However, the severity of the damages can be minimized by development of proper infrastructure which includes microzonation studies, appropriate construction procedures and earthquake resistant designs. The earthquake damaging effect depends on the source, path and site conditions. The earthquake ground motion is affected by topography (slope, hill, valley, canyon, ridge and basin effects), groundwater and surface hydrology. The seismic hazard damages are ground shaking, structural damage, retaining structure failures and lifeline hazards. The medium to large earthquake magnitude (< 6) reported in Ethiopia are controlled by the main Ethiopian rift System. The spatial and temporal variation of earthquake ground motion should be addressed using the following systematic methodology. The general approaches used to analyze damage of earthquake ground motions are probabilistic seismic hazard assessment (PSHA), deterministic seismic hazard assessment (DSHA) and dynamic site response analysis. PSHA considers all the scenarios of magnitude, distance and site conditions to estimate the intensity of ground motion distribution. Conversely, DSHA taken into account the worst case scenarios or maximum credible earthquake to estimate the intensity of seismic ground motion distribution. Furthermore, to design critical infrastructures, DSHA is more valuable than PSHA. The DSHA and PSHA ground motion distributions are estimated as a function of earthquake magnitude and distance using ground motion prediction equations (GMPEs) at top of the bedrock. Site response analysis performed to estimate the ground motion distributions at ground surface using dynamic properties of the soils such as shear wave velocity, density, modulus reduction, and material damping curves. Seismic hazard evaluation of Ethiopia shown that (i) amplification is occurred in the main Ethiopian Rift due to thick soil, (ii) the probability of earthquake recurrence due to active fault sources. The situation of active fault is oriented in the N-S direction. Ethiopia is involved in huge infrastructural development (including roads, industrial parks and railways), increasing population and agricultural activity in the main Ethiopian Rift system. In this activity, socio-economic development, earthquake and earthquake-generated ground failures need to be given attention in order to reduce losses from seismic hazards and create safe geo-environment.