Seismic Wave Attenuation Measurements Across The Main Ethiopian Rift and Adjacent Plateaus
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Date
2006-07
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Addis Ababa Universty
Abstract
As seismic wave propagates through earth materials, wave amplitude attenuates as a
result of several factors. From measurement of amplitude of seismic data,
attenuation measurement can be computed which can provide a viable tool for
lithology discrimination and peak ground motion prediction for the region under
study.
In this research, computation of attenuation coefficient is made from amplitude
measurements done on the seismic data collected during the Ethiopian Afar
Geoscientific lithopheric Experiment (EAGLE) which was undertaken in 2001-1003
project along profile I crossing the Main Ethiopian Rift, Western & Eastern
Plateaus. For the generation of seismic waves, explosives were detonated inside
boreholes and programmable seismic energy recorders called ‘‘ GURALP 6TD’’
were deployed on the surface at about 4-5 kilometer spacing across profile I. This
study particularly focuses on surface wave attenuation. The recorded surface wave
is processed so that the filtered amplitude is read appropriately.
1) In this study, we discuss the effect of the medium on seismic wave propagations
(particularly seismic wave attenuation) from which we model seismic wave
attenuation mathematically and analyze the 2D- graphical model of the region under
study. In doing so, we see the interrelationship between the attenuation coefficient
and distance, amplitude an distance, attenuation coefficient and frequency content of
the wave, and dissipation factors Q-1 and the frequency. Finally, the relationship
between attenuation coefficient and depth are also seen graphically and analytically.
From the model, the attenuating behaviors of the region are discussed from the
attenuation coefficient curve versus depth and evaluate the effects of the geology of
the region on wave propagation for the Main Ethiopian Rift, Western and Eastern
Ethiopian plateaus. The attenuation coefficient determined for the studied area
varies as a function of both offset and frequency of the wave. Depending on the
attenuating behaviors of the regions attempts have been made to determine the
various lithologies.
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Wave