New paleomagnetic result from the Ethiopian flood basalts in the Abbay (Blue Nile) and Kessem gorges     

Tesfaye Kidane  Bekele AbebeVincent Courtillot  Emilio Herrero 《Earth and Planetary Science Letters》2002,203(1):353-367

New paleomagnetic investigations on the Ethiopian trap series have been undertaken at the Abbay and Kessem gorges in an attempt to better constrain the 30 Ma paleomagnetic pole of Africa. We sampled six thick massive basaltic lava flows, totaling 230 m, from Abbay Gorge and 10 lava flows, 180 m in thickness, from Kessem Gorge. Detailed paleomagnetic analyses disclosed that the carriers of the characteristic remanent magnetization (ChRM) are different in different lava flows. These are mostly titanomagnetites, titanomaghemites, and magnetite minerals with a broad range of coercive force and blocking temperatures. The heating and cooling susceptibility vs. temperature curves, many of which are irreversible, may indicate chemical remagnetization, notably low temperature maghemitization. Only one flow (KS04) with a clear 580°C Curie temperature was apparently unaffected by chemical remagnetization. The ChRM direction of this flow is identical to that in other flows, which suggests that if and when remagnetization occurred, this was shortly after emplacement of the lava flows. All of the flows sampled have normal polarity. However, a reversed component of low to medium coercive force and low to medium unblocking temperature occurs in flow KS01 at Kessem Gorge. The ChRM directions for the 16 sites are D=3.1°, I=5.8° (α₉₅=12.7°). The paleomagnetic pole obtained from these is at λ=83.0°N, φ=193.3°E (A₉₅=9.0°). Comparison with three previous studies of the traps shows remarkable consistency and a number of means are derived and discussed. Two final preferred poles for the traps are at λ=79.0°N, φ=196.9°E (A₉₅=2.8°) when all 112 published flows are used, and λ=78.7°N, φ=209.4°E (A₉₅=3.4°) when only the 76 flows from the four more recently analyzed sections are included. Both are compatible with the recent reference synthetic pole for Africa of Courtillot and Besse [J. Geophys. Res. (2002) in press]. In that sense, the Ethiopian trap pole is not anomalous and does not require more of a non-dipolar contribution than indicated by analyses of the global paleomagnetic data base covering the last few million years.  相似文献   

The Role of Pre-existing Structures in the Origin, Propagation and Architecture of Faults in the Main Ethiopian Rift     

Tesfaye Korme  Valerio Acocella  Bekele Abebe 《Gondwana Research》2004,7(2):467-479

Four major fault systems oriented N–S to NNE–SSW, NE–SW, E–W and NW–SE are identified from Landsat Thematic Mapper (TM) images and a high resolution digital elevation model (DEM) over the Ethiopian Rift Valley and the surrounding plateaus. Most of these faults are the result of Cenozoic - extensional reactivation of pre-existing basement structures. These faults interacted with each other at different geological times under different geodynamic conditions. The Cenozoic interaction under an extensional tectonic regime is the major cause of the actual volcano-tectonic landscape in Ethiopia. The Wonji Fault Belt (WFB), which comprises the N–S to NNE–SSW striking rift floor faults, displays peculiar propagation patterns mainly due to interaction with the other fault systems and the influence of underlying basement structures. The commonly observed patterns are: curvilinear oblique-slip faults forming lip-horsts, sinusoidal faults, intersecting faults and locally splaying faults at their ends. Fault-related open structures such as tail-cracks, releasing bends and extensional relay zones and fault intersections have served as principal eruption sites for monogenetic Plio-Quaternary volcanoes in the Main Ethiopian Rift (MER).  相似文献   

Extenuating the parameters using HEC-HMS hydrological model for ungauged catchment in the central Omo-Gibe Basin of Ethiopia          下载免费PDF全文

Demisse Habtamu Semunigus  Ayalew Abebe Temesgen  Ayana Melkamu Teshome  Lohani Tarun Kumar 《地下水科学与工程》2021,9(4):317-325

Characteristics of ungauged catchments can be studied from the hydrological model parameters of gauged catchments. In this research, discharge prediction was carried out in ungauged catchments using HEC-HMS in the central Omo-Gibe basin. Linear regression, spatial proximity, area ratio, and sub-basin mean were amalgamated for regionalization. The regional model parameters of the gauged catchment and physical characteristics of ungauged catchments were collated together to develop the equations to predict discharge from ungauged catchments. From the sensitivity analysis, crop coefficient (CC), storage coefficient (R), constant rate (CR), and time of concentration (TC) are found to be more sensitive than others. The model efficiency was evaluated using Nash–Sutcliffe Efficiency (N_SE) which was greater than 0.75, varying between ?10% and +10% and the coefficient of determination (R²) was approximated to be 0.8 during the calibration and validation period. The model parameters in ungauged catchments were determined using the regional model (linear regression), sub-basin mean, area ratio, and spatial proximity methods, and the discharge was simulated using the HEC-HMS model. Linear regression was used in the prediction where p-value ≤ 0.1, determination coefficient (R²) = 0.91 for crop coefficient (CC) and 0.99 for maximum deficit (MD). Constant rate (CR), maximum storage (MS), initial storage (IS), storage coefficient (R), and time of concentration (TC) were obtained. The result is that an average of 30 m³/s and 15 m³/s as the maximum monthly simulated flow for ungauged sub-catchments, i.e. Denchiya and Mansa of the main river basin .  相似文献   

Plio-Quaternary volcanotectonic activity in the northern sector of the Main Ethiopian Rift: relationships with oblique rifting     

Mario Boccaletti  Roberto Mazzuoli  Marco Bonini  Teresa Trua  Bekele Abebe 《Journal of African Earth Sciences》1999,29(4):315

Deformation and magmatism within the 90 km wide northern Ethiopian Rift system is concentrated along a narrow zone - the Wonji Fault Belt. Two key areas (the Nazret-Dera and Asela-Ziway areas), located along the eastern margin of the north-northeast to northeast trending Main Ethiopian Rift, have been investigated in order to reconstruct the recent tectonomagmatic evolution of the northern branch of the Main Ethiopian Rift. In these areas, Early Pleistocene volcanic products (Wonji Group) overlie Pliocene volcanic rocks (Eastern Margin Unit). Detailed stratigraphical reconstructions have revealed the presence of several tectonomagmatic units which can be correlated between the two study areas. The stratigraphical and petrological study of these units outlined (1) the bimodal composition (basalts-pantellerites) of the oldest and youngest units and the unimodal character (pantellerites) of the products erupted during the intervening period; (2) the mainly fissural origin of the ignimbrites and oldest basalts; and (3) a mafic/felsic volumetric ratio of 1:5.The geological data suggest that, around the Pliocene-Quaternary boundary, a change in the stress field occurred in this Main Ethiopian Rift sector, passing from a direction of extension roughly orthogonal to the rift shoulders, to oblique rifting related to an east-west trending extension. In this framework the change in the style of volcanism observed in the Nazret-Dera and Asela-Ziway areas can be related to the change of the stress field. A new geodynamic model is presented for the Late Pliocene to Recent evolution of this sector of the Main Ethiopian Rift. According to this model, a large volume of rhyolitic products was erupted during an oblique rifting phase, following a previous period of pure extension. The change in the tectonic regime favoured partial melting of the underplated basalts as a decrease in the pressure and an elevation of isotherms occurred.  相似文献   

Features of groundwaters in basins shared between Ethiopia and Kenya and the implications for international legislation on transboundary aquifers     

Seifu Kebede  Abebe Ketema  Zenaw Tesema 《Hydrogeology Journal》2010,18(7):1685-1697

The implementation of laws relating to transboundary aquifers necessitates field knowledge so that the laws can be coincident with reality on the ground. The definition of ‘shared aquifer’ is more complex than the mere physically shared body of groundwater flowing from country A to country B. The border between Ethiopia and Kenya is characterized by low-volume groundwater storage and low transboundary flows. However, groundwater has visible environmental, social and economic functions. The characteristics of groundwater flow and storage in aquifers shared between Ethiopia and Kenya are different from those used in setting the foundation of the international legal framework on shared aquifers. By describing the characteristics of the groundwaters that are shared between Ethiopia and Kenya, this work demonstrates that the international legal framework is inadequate when applied in this region. The main inadequacies are: (1) international law does not specify the minimum volume of transboundary flow in an aquifer for it to qualify to be treated under the law, and (2) the physical aspects of water get more emphasis than the functions of groundwater. A more adequate international legal framework would be one that considers specific types of groundwater and local needs.  相似文献   

AIDS-affected children,family collectives and the social dynamics of care in Ethiopia     

Tatek Abebe 《Geoforum》2012,43(3):540-550

Many programmes for AIDS-affected children pursue resource-intensive and external interventions of care, and often place such children at the receiving end of the care continuum. The aim of this article is to explore from a socio-spatial perspective the capacities of families and children experiencing orphanhood and the policy significance of empowering both to address the growing challenge of orphan care in rural and urban Ethiopia. Drawing on participatory research (involving in-depth interviews, focus group discussions, story writing, photo essays, ranking, observation and household visits), the complex social dynamics of care and spatial diversities in the manifestations of the vulnerabilities, capacities, strengths, and potentials of children and their families are discussed. It is argued that rather than the lack of biological parents it is the combination of the absence of a carer and the presence of acute poverty and economic marginality that explain various forms of vulnerability in orphans and non-orphans. The article further argues that effective and sustainable care needs to be informed by identification and empowerment of ‘family collectives’ as sites of interventions. In doing so, it draws analytical attention to the importance of examining the socio-temporal processes of orphanhood and care, children’s changing circumstances, and family collectives’ variances in the capacity to provide support for them. Strategies for sustainable care should recognise the specific needs of AIDS-affected children and the resourceful ways in which they contribute to enhance the care-giving capacities of family collectives in the light of broader socio-cultural and political–economic contexts.  相似文献   

Dark energy cosmological models with cosmic string     

T. Vinutha  V. U. M. Rao  Bekele Getaneh  Molla Mengesha 《Astrophysics and Space Science》2018,363(9):188

In this paper we have studied the anisotropic Kantowski-Sachs, locally rotationally symmetric (LRS) Bianchi type-I and LRS Bianchi type-III geometries filled with dark energy and one dimensional cosmic string in the Saez-Ballester theory of gravitation. To get physically valid solution we take hybrid expansion law of the average scale factor which is a product of power and exponential type of functions that results in time dependent deceleration parameter (\(q\)). The equation of state parameter of dark energy (\(\omega _{\mathit{de}}\)) has been discussed and we have observed that for the three models it crosses the phantom divide line (\(\omega _{\mathit{de}} = -1\)) and shows quintom like behavior. The density of dark energy (\(\rho _{\mathit{de}}\)) is an increasing function of redshift and remains positive throughout the evolution of the universe for the three models. Moreover in Kantowski-Sachs and LRS Bianchi type-I geometries the dark energy density dominates the string tension density (\(\lambda \)) and proper density (\(\rho \)) throughout the evolution of the universe. The physical and geometrical aspects of the statefinder parameters (\(r,s\)), squared speed of sound (\(v_{s}^{2} \)) and \(\omega _{\mathit{de}}\)–\(\omega ^{\prime }_{\mathit{de}}\) plane are also discussed.  相似文献   

Evaluation of groundwater resource potential by using water balance model: A case of Upper Gilgel Gibe Watershed,Ethiopia          下载免费PDF全文

Abebe Wondmagegn Taye 《地下水科学与工程》2022,10(3):209-222

Groundwater resource potential is the nation’s primary freshwater reserve and accounts for a large portion of potential future water supply. This study focused on quantifying the groundwater resource potential of the Upper Gilgel Gibe watershed using the water balance method. This study began by defining the project area’s boundary, reviewing previous works, and collecting valuable primary and secondary data. The analysis and interpretation of data were supported by the application of different software like ArcGIS 10.4.1. Soil water characteristics of SPAW (Soil-plant-air-water) computer model, base flow index (BFI+3.0), and the water balance model. Estimation of the areal depth of precipitation and actual evapotranspiration was carried out through the use of the isohyetal method and the water balance model and found to be 1 664.5 mm/a and 911.6 mm/a, respectively. A total water volume of 875 829 800 m³/a is estimated to recharge the aquifer system. The present annual groundwater abstraction is estimated as 10 150 000 m³/a. The estimated specific yield, exploitable groundwater reserve, and safe yield of the catchment are 5.9%, 520 557 000 m³/a, and 522 768 349 m³/a respectively. The total groundwater abstraction is much less than the recharge and the safe yield of the aquifer. The results show that there is a sufficient amount of groundwater in the study area, and the groundwater resources of the area are considered underdeveloped.  相似文献   

The Central Main Ethiopian Rift is younger than 8 Ma: confirmation through apatite fission‐track thermochronology     

Tsegaye Abebe  Maria Laura Balestrieri  Giulio Bigazzi 《地学学报》2010,22(6):470-476

An isolated block of Precambrian basement rocks and Mesozoic sediments is exposed at Kella along the western margin of the Central Main Ethiopian Rift (MER), surrounded by Tertiary to Quaternary volcanic rocks. Apatite fission‐track thermochronology on two basement samples yielded ages of 7.2 ± 1.0 Ma and 6.7 ± 3.0 Ma and a long mean track length (>14.5 μm). Rapid Late Miocene cooling is attributed to denudation related to rifting. Despite the paucity of data, due to the absence of suitable lithologies in the area, our data confirm that the Central MER is younger than 8 Ma as recently proposed on the basis of field evidence and radiometric dating of volcanics. This implies that the Central MER formed after the Northern MER, indicating a diachronous development of this third arm of the Red Sea–Gulf of Aden–Ethiopian Rift system. Terra Nova, 00, 000–000, 2010  相似文献   

Accuracy evaluation of weather data generation and disaggregation methods at finer timescales     

Bekele Debele  R. Srinivasan  J. Yves Parlange 《Advances in water resources》2007

Availability of weather data at finer timescales such as hourly is vital in the application of dynamic physical and biological models. In this study, we have examined the suitability of various approaches (deterministic periodic versus stochastic) of disaggregating daily weather data into hourly data in the Cedar Creek watershed, TX, USA. We found the cosine function suitable to disaggregate daily maximum and minimum temperatures and wind speed data into respective hourly data. We also used a common logarithmic equation to compute vapor pressures from temperature data, and hence relative humidity (the ratio between actual and saturated vapor pressures multiplied by 100). Disaggregation following uniform distribution of daily rainfall over 24 h did not reproduce most statistical parameters computed from observed hourly rainfall data onsite. Conversely, both stochastic models formulated based on univariate (Hyetos) and multivariate (MuDRain) processes mimicked the measured hourly rainfall distributions very well. Overall, we found the MuDRain model superior, compared to other models to disaggregate daily rainfall data into hourly data.  相似文献