Inverse models of gravity data from the Red Sea–Aden–East African rifts triple junction zone     

Christel Tiberi  Cynthia Ebinger  Valérie Ballu  Graham Stuart  Befekadu Oluma 《Geophysical Journal International》2005,163(2):775-787

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Seismological Evidence of Active Faulting in the Tendaho Rift (Afar Triangle, Ethiopia)     

S. Gresta  D. Patanè  A. Daniel  L. Zan  A. Carletti  O. Befekadu 《Pure and Applied Geophysics》1997,149(2):357-374

—A temporary network has been used to study the seismic activity in the central-northern part of the Tendaho Rift (Afar Triangle, Ethiopia). Small size earthquakes (M < 2.5) characterize the seismicity during the time interval 1993–1994 when the seismic array was operating. Shocks are mainly located in the central part of the Tendaho rift and their epicentral distribution highlights a remarkable coincidence with NW-SE trending tectonically active structures. Focal depths are confined in the range of 3–8?km. ? The few acceptable fault plane solutions suggest the occurrence of both strike-slip and dip-slip rupture mechanisms, which are often characterized by a nodal plane oriented approximately NW-SE. ?A detailed study of earthquake waveforms using polarization analysis showed the occurrence of splitting phenomena for the S waves. Despite the differences in focal mechanisms, the similarity of the faster S-wave directions (NW-SE to NNW-SSE) suggests that the direction of geological structures and/or the systems of fractures adjacent to the faults could bias shear-wave propagation. The splitting time between fast and slow shear waves shows no systematic relationship with either hypocentral distance or focal depth, suggesting that the anisotropic volume is constrained to depths shallower than 3?km.  相似文献   

A heuristic probabilistic approach to estimating size-dependent mobility of nonuniform sediment     

Befekadu?Taddesse?WoldegiorgisEmail authorView author&#;s OrcID profile  Fu-Chun?Wu  Ann?Van?Griensven  Willy?Bauwens 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(6):1771-1782

This paper presents a heuristic probabilistic approach to estimating the size-dependent mobilities of nonuniform sediment based on the pre- and post-entrainment particle size distributions (PSDs), assuming that the PSDs are lognormally distributed. The approach fits a lognormal probability density function to the pre-entrainment PSD of bed sediment and uses the threshold particle size of incipient motion and the concept of sediment mixture to estimate the PSDs of the entrained sediment and post-entrainment bed sediment. The new approach is simple in physical sense and significantly reduces the complexity and computation time and resource required by detailed sediment mobility models. It is calibrated and validated with laboratory and field data by comparing to the size-dependent mobilities predicted with the existing empirical lognormal cumulative distribution function approach. The novel features of the current approach are: (1) separating the entrained and non-entrained sediments by a threshold particle size, which is a modified critical particle size of incipient motion by accounting for the mixed-size effects, and (2) using the mixture-based pre- and post-entrainment PSDs to provide a continuous estimate of the size-dependent sediment mobility.  相似文献