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

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

<p>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.</p>

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

2006 ◽  
Vol 259 (1) ◽  
pp. 307-321 ◽  
Author(s):  
D.G. Cornwell ◽  
G.D. Mackenzie ◽  
R.W. England ◽  
P.K.H. Maguire ◽  
L.M. Asfaw ◽  
...  
Keyword(s):  
High Precision ◽  
Crustal Structure ◽  
Gravity Data ◽  
Ethiopian Rift ◽  
Main Ethiopian Rift

scholarly journals Seismicity induced by fluid migration in the Main Ethiopian Rift

2020 ◽  
Author(s):  
Martina Raggiunti ◽  
Derek Keir ◽  
Carolina Pagli ◽  
Aude Lavayssiere
Keyword(s):  
Velocity Model ◽  
Normal Faults ◽  
Ethiopian Rift ◽  
Fluid Migration ◽  
Average Depth ◽  
Main Ethiopian Rift ◽  
3D Velocity Model ◽  
Geothermal Activity ◽  
Fluid Pore Pressure ◽  
Remote Sensing Mapping

<p>Faults can act as preferential degassing pathways for fluids of deep origin. Their migration and consequently variation of fluid pore pressure can cause a reduction of normal stress on the fault planes and trigger earthquakes. This can generate not only microseismicity but also events with significant magnitude. To understand this phenomenon, we studied the spatial, temporal and waveform characteristics of local seismicity from the northern sector of Main Ethiopian Rift (MER) of East Africa near Fentale and Dofen volcanoes. The seismic database contains events occurred in the MER from October 2001 to January 2003, and acquired by the Ethiopia Afar Geoscientific Experiment (EAGLE Project). The recorded events have been relocated with NLLoc using a new 3D velocity model derived from a wide-angle controlled source experiment. The relocated catalog contains a total of 1543 events with magnitudes between 0 and 4. The seismicity is mainly concentrated in two areas: near the border faults of the Ethiopian plateau and within the rift. On the border faults, events mostly occur down to 20 km depth, with an average depth of ~ 12 km. Within the rift, the events mostly happen down to 15 km depth, with an average depth of ~ 9 km. The seismicity is divided into several clusters aligned parallel to the rift direction, and in profile sections the clusters are mostly dipping steeply sub-vertical and dipping consistent with Andersonian normal faults. The analysis of the temporal-spatial distribution of earthquakes shows that some of the clusters are strongly concentrated in time and in space, and therefore swarm-like. To understand if the different clusters have been conditioned by fluid migration we have also analyzed the frequency content, release of seismic moment, and b-val is cut out. The link between earthquakes and fluid migration has also been explored by interpreting the distribution of seismicity using remote sensing mapping of faults, fumaroles and hydrothermal springs. Understanding where and how the fluid migration occurs will aid geothermal exploration efforts in the region, also improved knowledge of where geothermal activity is linked to seismicity has implications for seismic hazard estimation, which is very important for this densely and economically active areas.</p>

scholarly journals Main Ethiopian Rift landslides formed in contrasting geological settings and climatic conditions

2021 ◽  
Vol 21 (11) ◽  
pp. 3465-3487
Author(s):  
Karel Martínek ◽  
Kryštof Verner ◽  
Tomáš Hroch ◽  
Leta A. Megerssa ◽  
Veronika Kopačková ◽  
...  
Keyword(s):  
Normal Fault ◽  
Climatic Conditions ◽  
Arabian Plate ◽  
Ethiopian Rift ◽  
Vegetation Density ◽  
Regional Study ◽  
Main Ethiopian Rift ◽  
Landslide Occurrence ◽  
Precipitation Seasonality ◽  
Steep Slopes

Abstract. The Main Ethiopian Rift (MER), where active continental rifting creates specific conditions for landslide formation, provides a prospective area to study the influence of tectonics, lithology, geomorphology, and climate on landslide formation. New structural and morphotectonic data from central Main Ethiopian Rift (CMER) and southern Main Ethiopian Rift (SMER) support a model of progressive change in the regional extension from NW–SE to the recent E(ENE)–W(WSW) direction, driven by the African and Somali plates moving apart with the presumed contribution of the NNE(NE)–SSW(SW) extension controlled by the Arabian Plate. The formation and polyphase reactivation of faults in the changing regional stress field significantly increase the rocks' tectonic anisotropy, slope, and the risk of slope instabilities forming. According to geostatistical analysis, areas prone to landslides in the central and southern MER occur on steep slopes, almost exclusively formed on active normal fault escarpments. Landslide areas are also influenced by higher annual precipitation, precipitation seasonality, vegetation density, and seasonality. Deforestation is also an important predisposition because rockfalls and landslide areas typically occur on areas with bushland, grassland, and cultivated land cover. A detailed study on active rift escarpment in the Arba Minch area revealed similar affinities as in a regional study of MER. Landslides here are closely associated with steep, mostly faulted, slopes and a higher density of vegetation. Active faulting forming steep slopes is the main predisposition for landslide formation here, and the main triggers are seismicity and seasonal precipitation. The Mejo area situated on the uplifting Ethiopian Plateau 60 km east of the Great Rift Valley shows that landslide occurrence is strongly influenced by steep erosional slopes and a deeply weathered Proterozoic metamorphic basement. Regional uplift, accompanied by rapid headward erosion forming steep slopes together with unfavourable lithological conditions, is the main predisposition for landslide formation; the main triggers here are intense precipitation and higher precipitation seasonality.

Three-dimensional inversion of gravity data from the Main Ethiopian Rift

2000 ◽  
Vol 31 (2) ◽  
pp. 451-466 ◽  
Author(s):  
R. Mahatsente ◽  
G. Jentzsch ◽  
T. Jahr
Keyword(s):  
Gravity Data ◽  
Three Dimensional ◽  
Ethiopian Rift ◽  
Main Ethiopian Rift

Crustal structure of the Main Ethiopian Rift from gravity data: 3-dimensional modeling

1999 ◽  
Vol 313 (4) ◽  
pp. 363-382 ◽  
Author(s):  
R. Mahatsente ◽  
G. Jentzsch ◽  
T. Jahr
Keyword(s):  
Crustal Structure ◽  
Gravity Data ◽  
Ethiopian Rift ◽  
Main Ethiopian Rift ◽  
3 Dimensional ◽  
Dimensional Modeling

Mapping Geologic Structures from Gravity and Digital Elevation Model in the Ziway-Shala Lakes Basin; central Main Ethiopian Rift

2020 ◽  
Author(s):  
Hailemichael Kebede ◽  
Abera Alemu ◽  
Dessie Nedaw
Keyword(s):  
Digital Elevation Model ◽  
Gravity Data ◽  
Surface Structures ◽  
Ethiopian Rift ◽  
Main Ethiopian Rift ◽  
Near Surface ◽  
Subsurface Structures ◽  
Digital Elevation ◽  
Moho Depths ◽  
Elevation Model

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.

scholarly journals Main Ethiopian Rift landslides formed in contrasting geological settings and climatic conditions

2021 ◽  
Author(s):  
Karel Martínek ◽  
Kryštof Verner ◽  
Tomáš Hroch ◽  
Leta A. Megerssa ◽  
Veronika Kopačková ◽  
...  
Keyword(s):  
Active Tectonics ◽  
Normal Fault ◽  
Climatic Conditions ◽  
Ethiopian Rift ◽  
Vegetation Density ◽  
Regional Study ◽  
Main Ethiopian Rift ◽  
Landslide Occurrence ◽  
Precipitation Seasonality ◽  
Slope Instabilities

Abstract. The Main Ethiopian Rift (MER), where active continental rifting creates specific conditions for landslide formation, provides a prospective area to study the influence of tectonics, lithology, geomorphology, and climate on landslide formation. New structural and morphotectonic data from CMER and SMER support a model of progressive change in the regional extension from NW – SE to the recent E(ENE) – W(WSW) direction driven by the African and Somalian plates moving apart with the presumed contribution of the NNE(NE) – SSW(SW) extension controlled by the Arabic Plate. The formation and polyphase reactivation of faults in the changing regional stress-field significantly increase the rocks' tectonic anisotropy and the risk of slope instabilities forming. According to geostatistical analysis landslides in the central and southern MER occur on steep slopes, almost exclusively formed on active normal fault escarpments. Landslides are also influenced by higher annual precipitation, precipitation seasonality, vegetation density and seasonality. A detailed study on active rift escarpment in the Arba Minch area revealed similar affinities as in regional study of MER. Landslides here are closely associated with steep, mostly faulted, slopes and a higher density of vegetation. Active tectonics and seismicity are the main triggers. The Mejo area situated on the uplifting Ethiopian Plateau 60 km east of the Rift Valley shows that landslide occurrence is strongly influenced by steep erosional slopes and deeply weathered Proterozoic metamorphic basement. Rapid headward erosion, unfavourable lithological conditions and more intense precipitation and higher precipitation seasonality are the main triggers here.

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

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

<p>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.</p><p>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.</p>

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