ORCID Profile
0000-0002-8435-4927
Current Organisation
Addis Ababa University
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Publisher: American Geophysical Union (AGU)
Date: 07-2020
DOI: 10.1029/2020GC008935
Abstract: We combine numerical modeling of lithospheric extension with analysis of seismic moment release and earthquake b‐value in order to elucidate the mechanism for deep crustal seismicity and seismic swarms in the Main Ethiopian Rift (MER). We run 2‐D numerical simulations of lithospheric deformation calibrated by appropriate rheology and extensional history of the MER to simulate migration of deformation from mid‐Miocene border faults to ∼30 km wide zone of Pliocene to recent rift floor faults. While currently the highest strain rate is localized in a narrow zone within the rift axis, brittle strain has been accumulated in a wide region of the rift. The magnitude of deviatoric stress shows strong variation with depth. The uppermost crust deforms with maximum stress of 80 MPa, at 8–14 km depth stress sharply decreases to 10 MPa and then increases to a maximum of 160 MPa at ∼18 km depth. These two peaks at which the crust deforms with maximum stress of 80 MPa or above correspond to peaks in the seismic moment release. Correspondingly, the drop in stress at 8–14 km correlates to a low in seismic moment release. At this depth range, the crust is weaker and deformation is mainly accommodated in a ductile manner. We therefore see a good correlation between depths at which the crust is strong and elevated seismic deformation, while regions where the crust is weaker deform more aseismically. Overall, the bimodal depth distribution of seismic moment release is best explained by the rheology of the deforming crust.
Publisher: American Geophysical Union (AGU)
Date: 10-2022
DOI: 10.1029/2022TC007491
Abstract: Rift‐Rift‐Rift triple junctions are key features of emergent plate boundary networks during fragmentation of a continent. A key ex le of such a setting is the Afar triple junction where the African, Arabian and Somalian plates interact. We performed analog and numerical models simulating continental break‐up in a Rift‐Rift‐Rift setting to investigate the resulting structural pattern and evolution. We modified the ratio between plate velocities, and we performed single‐stage (with all plates moving at the same time) and two‐stage (where one plate first moves alone and then all the plates move simultaneously) models. Additionally, the direction of extension was changed to induce orthogonal extension in one of the three rift branches. Our models suggest that differential extension velocities in the rift branches determine the localization of the structural triple junction, which is located closer to the rift branch experiencing slower extension velocities. Furthermore, imposed velocities affect the deformation resulting in end‐member fault patterns. The effect of applying similar velocities in all rift arms is to induce a symmetric fault pattern (generating a Y‐shaped geometry). In contrast, a faster plate generates structures trending orthogonal to dominant velocity vectors, while faults associated with the movement of the slower plates remain subordinate (generating a T‐shaped pattern). Two‐stage models reveal high‐angle faults interacting at the triple junction, confirming that differential extension velocities strongly affect fault patterns. These latter models show large‐scale similarities with fault patterns observed in the Afar triple junction, providing insights into the factors controlling the structural evolution of this area.
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-11421
Abstract: The Main Ethiopian Rift (MER) is characterized by a significant along-strike variation in rift evolution and strain accommodation mechanisms. The northern MER is at a transitional stage, whereas the central MER is at an intermediate stage of rifting. Previous geophysical and geological observations suggest that rift obliquity, age of onset of rifting and/or presence/absence of magma could be responsible for the observed difference in deformation style. Here, we use the geodynamic modelling software ASPECT that has recently been coupled with the landscape evolution model FastScape to understand the role that surface processes (such as erosion and sedimentation) play in controlling the style of deformation at the central and northern sectors of the MER. Our results show that& the deformation in the central MER can be well explained by efficient surface processes. However, our models fail to fully capture the deformation in the northern MER implying that magma plays a significant role in this sector of the rift. We show that& the MER is a unique plate boundary where surface and magmatic processes control the style of deformation at different sectors within the same tectonic setting.&
Location: Germany
No related grants have been discovered for Ameha Atnafu Muluneh.