Seismic Wave Attenuation Measurements Across The Main Ethiopian Rift And Adjacent Plateaus

As seismic wave propagates through earth materials, wave amplitude attenuates as arnresult of several factors. From measurement of amplitude of seismic data,rnattenuation measurement can be computed which can provide a viable tool forrnlithology discrimination and peak ground motion prediction for the region underrnstudy.rnIn this research, computation of attenuation coefficient is made from amplitudernmeasurements done on the seismic data collected during the Ethiopian AfarrnGeoscientific lithopheric Experiment (EAGLE) which was undertaken in 2001-1003rnproject along profile I crossing the Main Ethiopian Rift, Western & EasternrnPlateaus. For the generation of seismic waves, explosives were detonated insidernboreholes and programmable seismic energy recorders called ‘‘ GURALP 6TD’’rnwere deployed on the surface at about 4-5 kilometer spacing across profile I. Thisrnstudy particularly focuses on surface wave attenuation. The recorded surface wavernis processed so that the filtered amplitude is read appropriately.rn1) In this study, we discuss the effect of the medium on seismic wave propagationsrn(particularly seismic wave attenuation) from which we model seismic wavernattenuation mathematically and analyze the 2D- graphical model of the region underrnstudy. In doing so, we see the interrelationship between the attenuation coefficientrnand distance, amplitude an distance, attenuation coefficient and frequency content ofrnthe wave, and dissipation factors Q-1 and the frequency. Finally, the relationshiprnbetween attenuation coefficient and depth are also seen graphically and analytically.rnFrom the model, the attenuating behaviors of the region are discussed from thernattenuation coefficient curve versus depth and evaluate the effects of the geology ofrnthe region on wave propagation for the Main Ethiopian Rift, Western and EasternrnEthiopian plateaus. The attenuation coefficient determined for the studied arearnvaries as a function of both offset and frequency of the wave. Depending on thernattenuating behaviors of the regions attempts have been made to determine thernvarious lithologies.

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