Northern Main Ethiopian Rift crustal structure from new high-precision gravity data

Abstract This study attempts to delineate subsurface lineaments for the tectonically and volcanically active region of the Ziway-Shala Lakes basin, central Main Ethiopian rift. Most of the previously mapped subsurface structures in the region under consideration focus on delineating crustal structures thicknesses and Moho depths undulations. Moreover, near-surface structures in the same region were mapped using analysis of Digital Elevation Model image data. On the other hand, there are few studies that have targeted in mapping geologic structures lying at intermediate depth levels between the shallower and deeper Earth. The objective of this research is thus to map the subsurface geologic structures/lineaments to an average depth of 3 km (crystalline basement layer depth) from surface using gravity data. These investigation results are validated by Digital Elevation Model extracted lineaments. Filtering techniques including derivative filters, upward-continuation and line module algorithm of PCI Geomatica are used to extract the gravity and topographic lineaments of the region. Orientation analyses of these subsurface and surface lineaments are made using line direction histogram of the QGIS software. Accordingly, the gravity subsurface lineaments mapped in this study are found to be dominantly oriented in the NNW-SSE to NW-SE and E-W direction on average. These results appear to be contrary to the NNE-SSW to NE-SW trending surface geologic structure mapped on the bases of actual field observation carried out by previous researchers and automatically extracted lineaments based on Digital Elevation Models data considered in this research. The subsurface lineaments mapped using gravity data coincide with the orientation of pre-existing subsurface structures crossing the rift orthogonally. These structural lineaments which are considered to be masked in the subsurface coincide with the orientation of the Mesozoic Ogaden rift as compared to the overlying surface structures which appear to coincide with the orientation of the Cenozoic Main Ethiopian rift.

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Crustal structure of the northern Main Ethiopian Rift from the EAGLE controlled-source survey; a snapshot of incipient lithospheric break-up

Geological Society London Special Publications ◽

10.1144/gsl.sp.2006.259.01.21 ◽

2006 ◽

Vol 259 (1) ◽

pp. 269-292 ◽

Cited By ~ 60

Author(s):

P.K.H. Maguire ◽

G.R. Keller ◽

S.L. Klemperer ◽

G.D. Mackenzie ◽

K. Keranen ◽

...

Keyword(s):

Crustal Structure ◽

Ethiopian Rift ◽

Main Ethiopian Rift ◽

Controlled Source ◽

Break Up

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Imaging magma storage in the Main Ethiopian Rift with 3-D Magnetotellurics

10.5194/egusphere-egu2020-9187 ◽

2020 ◽

Author(s):

Juliane Huebert ◽

Kathy Whaler ◽

Shimeles Fisseha ◽

Fiona Iddon ◽

Colin Hogg

Keyword(s):

Water Content ◽

Gravity Data ◽

Receiver Functions ◽

Magma Ascent ◽

Ethiopian Rift ◽

Volcanic Complex ◽

Magma Storage ◽

Energy Potential ◽

Melt Mixing ◽

Main Ethiopian Rift

The Main Ethiopian Rift (MER) as part of the large East African continental break-up zone is characterized by lateral extension and active volcanism. Rifting in the MER is magma assisted, with surface expressions of magmatism concentrated at en echelon Quaternary magmatic segments and off-axis linear features, but questions still remain about their respective roles in rifting.The storage and pathways of magma ascent are of great interest for the assessment of both geohazard and geothermal energy potential. Imaging magma storage throughout the crust and in the upper mantle can be achieved by geophysical deep sounding techniques such as magnetotellurics (MT). Through MT measurements it is possible to access the electrical conductivity of the subsurface, a parameter that is greatly sensitive to the melt and water content. We present new MT data from the Central MER and a three-dimensional model of conductivity of the crust, imaging across-rift magma storage not only under the well-developed central-axis silicic volcanic complex Aluto, but also under several off-axis basaltic monogenetic volcanic fields. The conductivity model supports the idea of bi-modal magma storage in the CMER and helps constrain the melt and water content in the crust through the use of petrological melt-mixing models. Integrating our findings with the results from seismic tomography and receiver functions as well as Bouguer gravity data and petrological observations allows a comprehensive picture of magma storage and pathways in the MER.

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Three dimensional inversion of gravity data from the main ethiopian Rift

Physics and Chemistry of the Earth Part A Solid Earth and Geodesy ◽

10.1016/s1464-1895(00)00058-2 ◽

2000 ◽

Vol 25 (4) ◽

pp. 365-373 ◽

Cited By ~ 7

Author(s):

G Jentzsch ◽

R Mahatsente ◽

T Jahr

Keyword(s):

Gravity Data ◽

Three Dimensional ◽

Ethiopian Rift ◽

Main Ethiopian Rift

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Local seismicity near the actively deforming Corbetti volcano in the Main Ethiopian Rift

10.5194/egusphere-egu2020-21585 ◽

2020 ◽

Author(s):

Derek Keir ◽

Aude Lavayssiere ◽

Tim Greenfield ◽

Mike Kendall ◽

Atalay Ayele

Keyword(s):

Gravity Data ◽

Local Population ◽

Normal Fault ◽

Velocity Model ◽

Ethiopian Rift ◽

Magma Body ◽

Main Ethiopian Rift ◽

Source Mechanisms ◽

Seismic Swarms ◽

The City

Corbetti is currently one of the fastest uplifting volcanoes globally, with strong evidence from geodetic and gravity data for a subsurface inflating magma body. A dense network of 18 stations has been deployed around Corbetti and Hawassa calderas between February 2016 and October 2017, to place seismic constraints on the magmatic, hydrothermal and fault slip processes occurring around this deforming volcano. We locate 122 events of magnitudes between 0.4 and 4.2 were located using a new local velocity model. The seismicity is focused in two areas: directly beneath Corbetti caldera and beneath the east shore of Lake Hawassa. The shallower 0-5km depth below sea level (b.s.l.) earthquakes beneath Corbetti are mainly focused in NW-elongated clusters at Urji and Chabbi volcanic centres. This distribution is interpreted to be mainly controlled by a northward propagation of hydrothermal fluids from a cross-rift pre-existing fault. Source mechanisms are predominantly strike-slip and different to the normal faulting away from the volcano, suggesting a local rotation of the stress-field. These observations, along with a low Vp/Vs ratio, are consistent with the inflation of a gas-rich sill, likely of silicic composition, beneath Urji. In contrast, the seismicity beneath the east shore of Lake Hawassa extends to greater depth (16 km b.s.l.). These earthquakes are focused on 8-10 km long segmented faults, which are active in seismic swarms. One of these swarms, in August 2016, is focused between 5 and 16 km depth b.s.l. along a steep normal fault beneath the city of Hawassa, highlighting the tectonic hazard for the local population.

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