scholarly journals Homogenized earthquake catalog and b-value mapping for Ethiopia and its adjoining regions

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Geremew Lamessa ◽  
Tilahun Mammo ◽  
Tarun K.Raghuvanshi
Keyword(s):  
Red Sea ◽  
B Value ◽  
Moment Magnitude ◽  
Ethiopian Rift ◽  
Rift System ◽  
Earthquake Catalog ◽  
Gulf Of Aden ◽  
East African Rift System ◽  
Main Ethiopian Rift ◽  
B Values

AbstractThe Ethiopian rift which is part of East African Rift system passes through the middle of the country making it one of the most seismically active regions in the world. Thus, significant and damaging earthquakes have been reported and recorded in the past in this region. A homogeneous earthquake catalog is of basic importance for studying the earthquake occurrence pattern in space and time and for many engineering applications including assessment of seismic hazard, estimation of peak ground accelerations and determination of long-term seismic strain rates.The first earthquake catalogue for Ethiopia was prepared by Pierre Gouin and later, different authors attempted to compile a catalogue using different time period intervals and different earthquake magnitude scales. The b-value mapping and its implication never done for Ethiopia and its environs. The main purpose of the study is therefore first compile and homogenize earthquake catalog of Ethiopia including Read Sea and Gulf of Aden regions into Moment magnitude Mw scale through completeness analysis in time and magnitudes. Secondly, mapping b-values for different Seismgenic regions and understand its implications for magma induced Seismicity in the regions.During the present study, a new homogenized earthquake catalog in moment magnitude scale (Mw), covering about 3814 events is prepared for Ethiopia including Red sea and Gulf of Aden regions. The present study area is bounded within Latitude (40N − 200)N and Longitude (340N − 480)N E and have a magnitude range of Mw (3.0–7.1) with a total coverage period of 56 years (1960 to 2016). The catalog has been analyzed for magnitude completeness (Mc) using Gutenberg’s Frequency Magnitude Distribution law and it is found to be complete respectively for Mc ≥ 4.6 ± 0.03, Mc ≥ 4.6 ± 0.03, Mc ≥ 3.2, Mc ≥ 3.1 and Mc ≥ 5.1 for Afar including red sea and Gulf of Aden, Afar rift and Dabbahu Volcano, Northern, Central, and Southern Main Ethiopian Rifts. Further, the corresponding average b-value of the regions Afar including Red Sea and Gulf of Aden, Afar and Dabbahu Volcano separately, Northern Main Ethiopian Rift, Central Main Ethiopian Rift and Southern Main Ethiopian Rift respectively are estimated to be 1.17 ± 0.05, 1.15 ± 0.05, 0.843, 0.826 and 1.03 with respective period of completeness from 2003 to 2014, 2005 to 2014, 2001 to 2003, 2001 to 2003 and 1960 to 2016 for the regions. Later, mapping of the b-values in the Gutenberg-Richter relation from the newly developed catalog was performed by binning the regions into minimum of 0.050x0.050 for Afar and Dabbahu region, 0.10x0.10 for Main Ethiopian rifts and 0.20x0.20 for the other regions. Thus, the b-value characteristics of various seismogenic zones within the area have been discussed. Hence, in this study, we clearly observed that magma chamber movement including mapping of volcanic centers and magmatic segments are mapped using b-values.

A discussion on the structure and evolution of the Red Sea and the nature of the Red Sea, Gulf of Aden and Ethiopia rift junction - The structure of afar and the northern part of the ethiopian rift

1970 ◽  
Vol 267 (1181) ◽  
pp. 331-338 ◽  
Keyword(s):  
Red Sea ◽  
Rift Zone ◽  
Ethiopian Rift ◽  
Crustal Extension ◽  
Gulf Of Aden ◽  
Lateral Shear ◽  
Structural Pattern ◽  
Main Ethiopian Rift ◽  
The Individual ◽  
Complex Faulting

The major structural feature of the northern part of the Main Ethiopian Rift is an en échelon belt of Quaternary tensional faulting with the individual faults trending approximately N 20° E. Farther north, towards central Afar, this structural pattern gives way to a zone of complex faulting. Northern Afar is dominated by a linear, axial central rift region, marked by active fissure volcanism, normal faulting and open tensional faults, all trending generally NNW. However, this central rift zone dies out northwards as it is traced towards the Gulf of Zula. Left-lateral shear along the length of the Main Ethiopian Rift is proposed as the cause of the en echelon tensional fault zone, which can be traced into Afar, but is apparently not continuous with the zone of faulting associated with the median trough of the Red Sea. The latter appears to be replaced in an en echelon fashion southwards by zones of crustal extension in central and northern Afar.

The Main Ethiopian Rift: Ongoing deformation inferred from earthquake mechanism

2021 ◽  
Author(s):  
Ameha Muluneh
Keyword(s):  
Tectonic Setting ◽  
Ethiopian Rift ◽  
Rift System ◽  
East African Rift System ◽  
East African ◽  
Active Deformation ◽  
Main Ethiopian Rift ◽  
African Rift ◽  
Rheological Modeling ◽  
Deformation Patterns

<div>The northern Main Ethiopian Rift (MER), which forms the northern part of the East African Rift System, offers an excellent tectonic setting to study the transition from continental to oceanic crust and also from tectonic to magmatic rifting. Opening of the rift started at 11 Myr ago. Until about 7 Ma, deformation was mainly accommodated at the rift border faults. Between 7 and 3 Ma, deformation migrated from the border faults to 20-30 km wide, 60 km long  magmatic segments. Earlier geodetic and field geological observations suggest that more than 80% of the present day opening of the rift is accommodated beneath these magmatic segments. On the contrary, recent observations indicate that deformation is more widespread than previously thought, with only 40% of the present day deformation being accommodated at the rift centre. </div><div> </div><div>Detailed understanding on the depth and epicentral distribution of earthquakes provides an important constraint on how strain is partitioned between the rift floor and border faults. Here I use high resolution earthquake catalogue and thermo-rheological modeling to constrain the active deformation patterns in the northern MER by assuming that the long term properties of the lithosphere represent the short term earthquake cycle. The final result of this study has significant implications for the location and magnitude of seismic hazard in the rift. </div>

Eruptive frequency of the Bora-Baricha-Tullu Moye (BBTM) volcanic system in the Central Main Ethiopian Rift

2021 ◽  
Author(s):  
Amdemichael Zafu Tadesse ◽  
Karen Fontijn ◽  
Abate Assen Melaku ◽  
Ermias Filfilu Gebru ◽  
Victoria Smith ◽  
...  
Keyword(s):  
Late Quaternary ◽  
Volcanic Eruptions ◽  
Volcanic Field ◽  
Tectonic Activity ◽  
Explosive Eruptions ◽  
Ethiopian Rift ◽  
Rift System ◽  
Diagnostic Features ◽  
Volcanic System ◽  
Main Ethiopian Rift

<p>The Main Ethiopian Rift (MER) is the northern portion of the East African Rift System and separates the Eastern and Western plateaus of Ethiopia. The recent volcanic and tectonic activity is largely focused within the rift basin along a 20 km wide zone on the rift floor. Large silicic volcanic complexes are aligned along this central rift axis but their eruptive histories are not well constrained.</p><p>The Bora-Baricha-Tullu Moye (BBTM) volcanic field is situated in the central Main Ethiopian Rift and has a different appearance than the other MER volcanic systems. The BBTM constitutes several late Quaternary edifices, the major ones are: Tullu Moye, Bora and Baricha. In addition, there are multiple smaller eruptive vents (e.g. Oda and Dima), cones, and domes across the ca. 20 X 20 km wide area. Currently, there is very little information on the frequency and magnitude of past volcanic eruptions. We present a new dataset of field observations, componentry, petrography, geochronology (<sup>40</sup>Ar/<sup>39</sup>Ar), and glass major and trace element chemistry. The data are assessed as potential fingerprints to assign diagnostic features and correlate units across the area, and establish a tephrostratigraphic framework for the BBTM volcanic field.</p><p>Two large-volume and presumably caldera-forming eruptions are identified, the younger of which took place at 100 ka. The volcanic products exposed in the BBTM area show that the volcanic field has undergone at least 20 explosive eruptions since then. The post-caldera eruptions have comenditic (Tullu Moye) and pantelleretic (Bora and Baricha) magma compositions. Other smaller edifices such as Oda and Dima also erupted pantelleritic magmas, and only differ slightly in composition than tephra of Bora and Baricha. Tullu Moye had two distinct explosive eruptions that dispersed tephra up to 14 km away and on to the eastern plateau. Bora and Baricha together had at least 8 explosive eruptions. Their deposits can be distinguished by their light grey color and unique lithic components. Oda had 7 eruptions, the most recent of which generated a pyroclastic density current that travelled up to 10 km away from the vent. Dima experienced at least 3 eruptions, generating tephra with a bluish-grey colour.</p><p>This mapping and compositional analysis of the deposits from the BBTM in the MER indicates that the region has been more active in the last 100 ka than previously thought, which has implications for hazards assessments for the region.</p>

scholarly journals A review on the multi-criteria seismic hazard analysis of Ethiopia: with implications of infrastructural development

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Alemayehu Ayele ◽  
Kifle Woldearegay ◽  
Matebie Meten
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Active Fault ◽  
Site Response ◽  
Seismic Hazard Assessment ◽  
Earthquake Ground Motion ◽  
Response Analysis ◽  
Ethiopian Rift ◽  
Rift System ◽  
Main Ethiopian Rift

AbstractEarthquake is a sudden release of energy due to faults. Natural calamities like earthquakes can neither be predicted nor prevented. However, the severity of the damages can be minimized by development of proper infrastructure which includes microzonation studies, appropriate construction procedures and earthquake resistant designs. The earthquake damaging effect depends on the source, path and site conditions. The earthquake ground motion is affected by topography (slope, hill, valley, canyon, ridge and basin effects), groundwater and surface hydrology. The seismic hazard damages are ground shaking, structural damage, retaining structure failures and lifeline hazards. The medium to large earthquake magnitude (< 6) reported in Ethiopia are controlled by the main Ethiopian rift System. The spatial and temporal variation of earthquake ground motion should be addressed using the following systematic methodology. The general approaches used to analyze damage of earthquake ground motions are probabilistic seismic hazard assessment (PSHA), deterministic seismic hazard assessment (DSHA) and dynamic site response analysis. PSHA considers all the scenarios of magnitude, distance and site conditions to estimate the intensity of ground motion distribution. Conversely, DSHA taken into account the worst case scenarios or maximum credible earthquake to estimate the intensity of seismic ground motion distribution. Furthermore, to design critical infrastructures, DSHA is more valuable than PSHA. The DSHA and PSHA ground motion distributions are estimated as a function of earthquake magnitude and distance using ground motion prediction equations (GMPEs) at top of the bedrock. Site response analysis performed to estimate the ground motion distributions at ground surface using dynamic properties of the soils such as shear wave velocity, density, modulus reduction, and material damping curves. Seismic hazard evaluation of Ethiopia shown that (i) amplification is occurred in the main Ethiopian Rift due to thick soil, (ii) the probability of earthquake recurrence due to active fault sources. The situation of active fault is oriented in the N-S direction. Ethiopia is involved in huge infrastructural development (including roads, industrial parks and railways), increasing population and agricultural activity in the main Ethiopian Rift system. In this activity, socio-economic development, earthquake and earthquake-generated ground failures need to be given attention in order to reduce losses from seismic hazards and create safe geo-environment.

scholarly journals Box Counting Fractal Dimension and Frequency Size Distributon of Earthquakes in the Central Himalaya Region

2021 ◽  
Vol 26 (2) ◽  
pp. 127-136
Author(s):  
Ram Krishna Tiwari ◽  
Harihar Paudyal
Keyword(s):  
Fractal Dimension ◽  
High Stress ◽  
High Strength ◽  
B Value ◽  
Earthquake Catalog ◽  
Central Himalaya ◽  
Study Region ◽  
B Values ◽  
Box Counting ◽  
Earthquake Distribution

To establish the relations between b-value and fractal dimension (D0) for the earthquake distribution, we study the regional variations of those parameters in the central Himalaya region. The earthquake catalog of 989 events (Mc = 4.0) from 1994.01.31 to 2020.10.28 was analyzed in the study. The study region is divided into two sub-regions (I) Region A: 27.3°N -30.3°N and 80°E -84.8°E (western Nepal and vicinity) and (II) Region B: 26.4°N -28.6°N and 84.8°E -88.4°E (eastern Nepal and vicinity). The b-value observed is within the range between 0.92 to 1.02 for region A and 0.64 to 0.74 for region B showing the homogeneous nature of the variation. The seismic a-value for those regions ranges respectively between 5.385 to 6.007 and 4.565 to 5.218. The low b-values and low seismicity noted for region B may be related with less heterogeneity and high strength in the crust. The high seismicity with average b-values obtained for region A may be related with high heterogeneity and low strength in the crust. The fractal dimension ≥1.74 for region A and ≥ 1.82 for region B indicate that the earthquakes were distributed over two-dimensional embedding space. The observed correlation between D0 and b is negative for western Nepal and positive for eastern Nepal while the correlation between D0 and a/b value is just opposite for the respective regions. The findings identify both regions as high-stress regions. The results coming from the study agree with the results of the preceding works and reveal information about the local disparity of stress and change in tectonic complexity in the central Himalaya region.

A discussion on the structure and evolution of the Red Sea and the nature of the Red Sea, Gulf of Aden and Ethiopia rift junction - The structural pattern of the Afro-Arabian rift system in relation to plate tectonics

1970 ◽  
Vol 267 (1181) ◽  
pp. 383-391 ◽  
Keyword(s):  
Red Sea ◽  
Plate Tectonics ◽  
Structural Model ◽  
Structural Features ◽  
Dead Sea ◽  
Strike Slip ◽  
Rift System ◽  
Gulf Of Aden ◽  
Structural Pattern ◽  
The Dead

The structural pattern of the Afro-Arabian rift system suggests the influence of transcurrent faulting in the development of the main branches of the system, particularly along the Dead Sea rift, the Gulf of Suez and Red Sea, and the eastern rift of Africa. Geophysical evidence indicates that the Red Sea and Gulf of Aden formed as a result of the separation of the Arabian and African continental blocks. Previously determined rotation poles about which the blocks separated neglect some structural features of the region. A satisfactory refit of Arabia to Africa can­ not be made unless some relative movements of parts of the Africa block too place. It is proposed that dextral strike-slip movements took place between Africa and Arabia along the Red Sea and that sinistral strike-slip movements occurred along the Dead Sea rift. In addition, rotation of the E. Kenya-Somalia block east of the eastern rift of Africa took place. Structural and palaeomagnetic evidence supports such movements. The structural model is compatible with the observed tectonic pattern and provides a genetic link between the formation of the Red Sea, Gulf of Aden and the African rifts.

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