Crustal Structure of the Northeast African Rift System from Receiver Function Analysis
| dc.contributor.advisor | Atalay Ayele (Professor) | |
| dc.contributor.author | Birhanu Abera | |
| dc.date.accessioned | 2024-02-15T08:11:59Z | |
| dc.date.available | 2024-02-15T08:11:59Z | |
| dc.date.issued | 2023-05-16 | |
| dc.description.abstract | This study examines the crustal structure in different regions, including Afar, Northwest (NW) plateau, Southeast (SE) plateau, Northern Main Ethiopian Rift (NMER), and Central Main Ethiopian Rift (CMER). High-quality teleseismic data (Mb > 6.0) with epicentral distances of 30◦ to 90◦ were analysed. The data were collected between 2000 and 2013 from 27 temporary broadband stations in Ethiopia and Eritrea, and between February 2015 and October 2016 from 17 stations of the RiftVolc broadband network. The study reveals consistent seismic velocity in the Afar crust, except in magmatic segments. These segments have a shallow layer with fast Vs (4.5 km/s) at depths of 6-14 km. Below this layer, Vs decreases (< 3.2 km/s), and the Vp/Vs ratio increases (2.0) at lower crustal depths (20-25 km). This suggests partial melting beneath the lower crust, particularly in the western Afar region and magmatic segments. The NW Plateau exhibits fast Vs (4-4.7 km/s) in its crust, with some regions showing slow Vs (3.2 km/s) and high Vp/Vs (1.85-2.0) at mid-crustal depths (10-25 km). Partial melt is observed in specific mid-crustal areas, possibly due to the extension of the plateau or melt migration from the rift. The uppermost crust (depth <6 km) in the NMER and CMER has slow Vs due to sedimentary and/or volcanic layers. Crustal Vs exhibits lateral and depth variations. Slow Vs (∼2-3 km/s) is observed beneath volcanic centres in the upper-mid crust, while the lower crust consistently shows slow Vs (Vs < 3.5 km/s). The slow lower crust is associated with high Vp/Vs ratios (1.9-2.0). A low Vs and a small fraction (< 5%) of high Vp/Vs material in the rift system indicate possible partial melt, which is widespread in the rift valley as segmented and localized features. These findings suggest that partial melt in the lower crust beneath active magmatic rifts is more significant than previously thought. The presence of a substantial melt reservoir in the lower crust highlights the role of magmatism in crustal extension and its influence on the evolution of the rift system. In contrast, the Eastern Plateau exhibits uniform and faster Vs, with a distinct velocity contrast between the crust and upper mantle, indicating less deformation compared to the central rift zone. The estimated Moho depth in Afar ranges from 26-30 km, showing a gradual transition compared to other areas studied. Furthermore, the NW Plateau has a Moho depth ranging from 36-44 km, while the SE Plateau has a depth ranging from 36-42 km. These findings have implications for understanding continental rifting mechanisms, magmatic system formation, and long-term lithospheric evolution. | |
| dc.identifier.uri | https://etd.aau.edu.et/handle/123456789/1789 | |
| dc.language.iso | en_US | |
| dc.publisher | Addis Ababa University | |
| dc.subject | Crustal Structure | |
| dc.subject | Northeast African Rift | |
| dc.subject | Function Analysis | |
| dc.subject | Northeast African Rift System | |
| dc.title | Crustal Structure of the Northeast African Rift System from Receiver Function Analysis | |
| dc.type | Thesis |