Browsing by Author "Abera, Birhanu"

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    Cellular Automata Techniques: an Approach to Model and Simulate Brownian particles Diffusion
    (Addis Ababa University, 2010-06) Abera, Birhanu; Bekele, Mulugeta (PhD)
    In this project, we investigate the di usion coe cient of Brownian particles which are randomly generated on a two dimensional grid. By using the cellular automata techniques we investigate mean square displacement (MSD) and root mean square displacement (RMSD) of particles for xed percent of concentration. We nd the MSD and RMSD of particles at di erent values of concentration. In addition to these, we investigate MSD and RMSD of particles for xed and di erent values of concentration at di erent time steps for a given number of cells
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    An Inversion Model of Receiver Function for Moho Depth Determination Beneath Locations of the Ethiopian Seismic Network Stations and their Surroundings
    (Addis Ababa Universty, 2016-06) Abera, Birhanu; Ayele, Atalay (PhD)
    Moho depths or crustal thicknesses at four stations of the Ethiopian Seismic Station Network (ESSN) are estimated from Receiver Functions studies. We used high quality seismic data recorded at ANKE (Ankober), DILA (Dila), HARE (Harar) and SEME (Semera) stations for earthquakes located at epicentral distances ranging from 30o to 100o and magnitude M 5:5. We applied frequency domain deconvolution technique to remove all effects from the earthquakes source and propagation path to make the RFs dependent only on the structure beneath the seismic stations. A linearized-iterative inversion is applied on the generated radial component of the Receiver functions. From the four stations in the study, the minimum number of teleseismic earthquakes is 14 for Harar while the maximum is 39 for Ankober. The estimated values for the Moho depth are 42 1:7km, 36 2km, 38 2kmand 26 2kmfor Ankober, Dila, Harar and Semera respectively. We have achieved a reasonably good fit between the observed and synthetic RFs which demonstrates the goodness of the inversion. The lowest Moho depth is observed for Semera station which implies a thinned crust while the highest crustal thickness is achieved for Ankober that lies along the western plateau margin. The second low Moho depth is calculated for Dila station while the one for Harar is an intermediate one. Our results agree with previous observations which strengthens the fact that Moho depths estimated for stations that lie within the rift and rift margins are lower than those located in the plateaus. On the other hand, our RFs inversions show low velocity gradient at about 15km depth at Semera stations while high velocity gradient is noticed at Ankober station. This may imply a cooled magma from previous dike or sill intrusions beneath Ankober station while the observation at Semera indicates the existence of melt at that depth