The Wonji fault belt (Main Ethiopian Rift): structural and geomorphological constraints and GPS monitoring

Abstract

The Wonji Fault Belt (WFB), Main Ethiopian Rift, forms a network of faults oriented NNE-SSW with a Quaternary direction of extension oriented c. N95° E. Faults are spaced between 0.5 and 2 km, show a fresh steep scarp, recent activity and slip rates of up to 2.0 mm a−1. This high value of deformation along the rift floor with respect to the plate separation rates suggests that most of the active strain could be accommodated by magma-induced faulting within the rift. However, the mountain front morphology associated with a displacement of 300–400 m since the Middle Pleistocene, tilted-blocks, brittle-seismic fault rock fabric and historical earthquakes with M>6 support a tectonic origin of the Asela boundary fault. Therefore, we propose a model that considers the possible coexistence of both magmatic deformation at the rift floor and brittle faulting at the rift margin. We also report the data relative to a GPS network installed in December 2004, along two transects across the WFB, between Asela and the Ziway Lake.

Formation and stability of magmatic segments in the Main Ethiopian and Afar rifts

“…This pattern of strain is consistent with the broad zone of collapse calderas and faults observed at the surface (e.g. Pizzi et al, 2006). Further north in the FentaleDofen magmatic segment, seismicity along the rift axis is predominantly concentrated at 9-14 km depth within a narrower (30 km wide) axial graben that is coincident with a 20-30 km-wide zone of mafic intrusions.…”

“…Fernandes et al (2004) predict 6-7 mm/yr opening in a direction N95 ± 5, compared to ∼ 20 mm/yr at N50 in the southernmost Red Sea (Vigny et al, 2006). Pizzi et al (2006) found an extension direction of N95. Keir et al (2006) estimated an extension direction of N103 ± 12 from an inversion of focal mechanism solutions for tectonic earthquakes, which is similar to the N109 opening direction from a single geodetic profile across the rift (Bilham et al, 1999).…”

“…The N10-striking faults and aligned volcanic chains within the Quaternary magmatic segments are oblique to the N45 strike of the large offset, Miocene border faults bounding the MER, which themselves are oblique to the N20 trend of the southern MER (e.g. Meyer et al, 1975;Pizzi et al, 2006) (Figs. 1 and 2).…”

Paleomagnetic constraints on stratigraphy and rift-related tectonics of Pliocene and Early Pleistocene volcano-sedimentary strata: the Mt. Galili hominid research area, Southern Afar Depression, Ethiopia

“…Since 11 Ma the northern part of the MER was already opening out into the stretched Afar depression (Hendrie et al, 1994;Tesfaye et al, 2003;Wolfenden et al, 2004). Generally, the MER opened at a rate of about 2.5 to 5 mm/a in ESE-WNW direction during Miocene to Pliocene times (Wolfenden et al, 2004), whereby large, discontinuous normal border faults developed (Pizzi et al, 2006;Tesfaye et al, 2008). Subsequently, continuous rift extension focused on newly developed magmatic segments of Quaternary age (Ebinger and Casey, 2001;Casey et al, 2006;Keir et al, 2006;Corti, 2009) which were connected with coeval rift basins, interpreted as embryonic oceanic spreading centres (Hayward and Ebinger, 1996;Manighetti et al, 1998;Ebinger and Casey, 2001).…”

Geoheritage conservation in Ethiopia: the case of the Simien Mountains

“…With an average width of about 70 km, it is the narrowest part of the Ethiopian rift system (e.g., Beyene & Abdelsalam 2005). It is bordered by discontinuous series of large, vertical to sub-vertical Miocene aged normal faults (Pizzi et al 2006). The main rift is dotted with a series of Quaternary rift basins where current rift extension and both basaltic and silicic magmatism is focused (Hayward & Ebinger 1996).…”