Northern Red Sea Rift Research Articles

Weakened continental lithosphere beneath the northern Red Sea inferred from elastic thickness

The northern Red Sea (NRS) is considered an extended continental region that has resulted in a rift system. Gravity and bathymetry data were used to estimate the Moho depth and the elastic thickness Te of the lithosphere beneath the NRS region to characterize its flexural rigidity and understand its mechanical behavior. Focusing on the Mabahiss Deep in NRS, we analyzed the lithosphere's flexural rigidity. The observed long-wavelength positive Bouguer anomaly is attributed to crustal thinning and lithospheric mantle uplift. The crustal thickness varies from 28 km in coastal areas to 24 km beneath the axial rift, supporting a regional compensation model over the Airy model. Forward modeling suggests that the optimal model explaining the regional Bouguer anomaly is a flexural model with Te equal to 7 km, indicating a weak and irregular continental crust. The primary factor contributing to this weakness is heating activity. Given the weakened state of the crust and the ongoing extension in the region, the NRS rift could evolve into a rupture, potentially leading to the formation of oceanic crust.

The modest seismicity of the northern Red Sea rift

The modest seismicity of the northern Red Sea rift

The major tectonic boundaries of the Northern Red Sea rift, Egypt derived from geophysical data analysis

AbstractIn the present study, we have attempted to map the plate boundary between Arabia and Africa at the Northern Red Sea rift region including the Suez rift, Gulf of Aqaba-Dead Sea transform and southeastern Mediterranean region by using gravity data analysis. In the boundary analysis method which was used; low-pass filtered gravity anomalies of the Northern Red Sea rift region were computed. Different crustal types and thicknesses, sediment thicknesses and different heat flow anomalies were evaluated. According to the results, there are six subzones (crustal blocks) separated from each other by tectonic plate boundaries and/or lineaments. It seems that these tectonic boundaries reveal complex structural lineaments, which are mostly influenced by a predominant set of NNW–SSE to NW–SE trending lineaments bordering the Red Sea and Suez rift regions. On the other side, the E–W and N–S to NNE–SSW trended lineaments bordering the South-eastern Mediterranean, Northern Sinai and Aqaba-Dead Sea transform regions, respectively. The analysis of the low pass filtered Bouguer anomaly maps reveals that the positive regional anomaly over both the Red Sea rift and South-eastern Mediterranean basin subzones are considered to be caused by the high density of the oceanic crust and/or the anomalous upper mantle structures beneath these regions whereas, the broad medium anomalies along the western half of Central Sinai with the Suez rift and the Eastern Desert subzones are attributed to low-density sediments of the Suez rift and/or the thick upper continental crustal thickness below these zones. There are observable negative anomalies over the Northern Arabia subzone, particularly in the areas covered by Cenozoic volcanics. These negative anomalies may be attributed to both the low densities of the surface volcanics and/or to a very thick upper continental crust. On the contrary, the negative anomaly which belongs to the Gulf of Aqaba-Dead Sea transform zone is due to crustal thickening (with limited heat flow values) below this region. Additionally in this study, the crustal thinning was investigated with heat flow, magnetic and free air gravity anomalies in the Northern Red Sea rift region. In fact, the crustal thinning of the study area was also proportional to the regions of observable high heat flow values. Finally, our results were found to be well correlated with the topography, free air, aeromagnetic and heat flow dataset profiles crossing most of the study area.

Mapping b-values beneath Abu Dabbab from June to August 2004 earthquake swarm

Abu Dabbab area is considered as one of the most active earthquake sources in Egypt. It is defined by its swarm type activity, and complicated stress pattern. This study was conducted to evaluate the two and three dimensional spatial distribution of b-value at Abu Dabbab area (Margin of the northern Red Sea Rift, Egypt). The gridding technique of Wiemer and Wyss (1997) was used to compute b-value using ZMAP software. The b-value is calculated from a catalog consisting of 850 well-located earthquakes, which were recorded from 1st June to August 2004, using the maximum likelihood method. These earthquakes were recorded by temporary digital seismic network, with magnitudes ranging from −1 to 3.4ML. It is important to mention that the variations of b-value with time cannot be easily detected for a short period. Hence, this study has been carried out to examine the variations of b-value in space. The computed b-value in the Abu Dabbab area does not follow a uniform distribution. A small volume of anomalously high b-value (b>1.8) exists in the central part of the area at a depth between 6 and 9km. This seems to agree with the reported low velocity value derived from previous P-wave travel time tomography studies (Hosny et al., 2009) and the low Q value (Abdel-Fattah et al., 2008). The existence of an anomalously high b-value region may be attributed to the presence of a magma reservoir or dyke zone beneath the northern Red Sea Rift that causes an intensively heterogeneous fractured crust or unusually high pore pressure.

Stress analysis and tectonic trends of southern Sinai Peninsula, using potential field data analysis and anisotropy technique

Abstract The aim of the present work is to evaluate the stress direction and the tectonic trends of the study area using magnetic anisotropy and potential field data interpretations (Bouguer and aeromagnetic). The specific objective of the gravity and aeromagnetic interpretation is to establish the trend and depth of the structural configuration of the basement rocks. Horizontal gradient techniques could to delineate directions of deep sources and enabled tracing several faults, lineaments and tectonic boundaries of basement rocks. The trend analysis shows N40°–50°W, N10°–20°W and N10°–20°E which may be related to the Gulf of Suez, Red Sea and Gulf of Aqaba stresses. However, Euler Deconvolution technique was applied using the aeromagnetic data to provide reliable information about penetrated source depth (100 m and ∼10.0 km) and trends of the subsurface sources (principally in NW and NE directions). Moreover, representative 72 oriented rock samples have been collected from seven sites in the study area. The rock magnetic properties and magnetic anisotropy analysis have been determined for all the studied samples. The interpretation clearly defined magnetic lineation at all sites and anisotropy of magnetic susceptibility (AMS) parameters. The stress direction of the studied area has been evaluated using magnetic anisotropy and geophysical analysis. Generally the estimated geophysical data analysis (Bouguer and aeromagnetic) are well consistent with the AMS interpretations of this study. The results indicated that the directions of predominant faults and foliations are NW-SE (related to the Gulf of Suez and Red Sea rifting) which indicate that the main stress and tectonic trend is NE-SW, which is more predominant in southern Sinai region. Moreover, it is clear that, the studied area was affected also by less predominant sources trended in NE-SW direction, which related to the tectonic activity of Gulf of Aqaba. The least predominant is north 40°–50° east that is probably due to the Syrian Arc system. Finally, our results are extremely coincided with the previous stress directions derived from geological, seismological and tectonic analysis in northern Red Sea rift, Gulf of Suez and Sinai regions.

Estimating Curie Point Depth and Heat Flow Map for Northern Red Sea Rift of Egypt and Its Surroundings, from Aeromagnetic Data

In this study, we aim to map the Curie point depth surface for the northern Red Sea rift region and its surroundings based on the spectral analysis of aeromagnetic data. Spectral analysis technique was used to estimate the boundaries (top and bottom) of the magnetized crust. The Curie point depth (CPD) estimates of the Red Sea rift from 112 overlapping blocks vary from 5 to 20 km. The depths obtained for the bottom of the magnetized crust are assumed to correspond to Curie point depths where the magnetic layer loses its magnetization. Intermediate to deep Curie point depth anomalies (10–16 km) were observed in southern and central Sinai and the Gulf of Suez (intermediate heat flow) due to the uplifted basement rocks. The shallowest CPD of 5 km (associated with very high heat flow, ~235 mW m−2) is located at/around the axial trough of the Red Sea rift region especially at Brothers Island and Conrad Deep due to its association with both the concentration of rifting to the axial depression and the magmatic activity, whereas, beneath the Gulf of Aqaba, three Curie point depth anomalies belonging to three major basins vary from 10 km in the north to about 14 km in the south (with a mean heat flow of about 85 mW m−2). Moreover, low CPD anomalies (high heat flow) were also observed beneath some localities in the northern part of the Gulf of Suez at Hammam Fraun, at Esna city along River Nile, at west Ras Gharib in the eastern desert and at Safaga along the western shore line of the Red Sea rift. These resulted from deviatoric tensional stresses developing in the lithosphere which contribute to its further extension and may be due to the opening of the Gulf of Suez and/or the Red Sea rift. Furthermore, low CPD (with high heat flow anomaly) was observed in the eastern border of the study area, beneath northern Arabia, due to the quasi-vertical low-velocity anomaly which extends into the lower mantle and may be related to volcanism in northern Arabia. Dense microearthquakes seem to occur in areas where the lateral gradients of the CPD are steep (e.g. entrance of the Gulf of Suez and Brothers Island in the Red Sea). These areas may correspond to the boundaries between high and low thermal regions of the crust. Thus, the variations in the microseismic activity may be closely related to thermal structures of the crust. Indeed, shallow cutoff depths of seismicity can also be found in some geothermal areas (e.g. western area of Safaga city along the Red Sea coastal region and at Esna city along the River Nile). These facts indicate that the changes in the thickness of the seismogenic layer strongly depend on temperature. Generally, the shallow Curie point depth indicates that some regions in our study area are promising regions for further geothermal exploration particularly in some localities along the River Nile, Red Sea and Gulf of Suez coastal regions.

Applying the regularized derivatives approach in Euler deconvolution and modeling geophysical data to estimate the deep active structures for the northern Red Sea Rift region, Egypt

The Red Sea is considered to be a typical example of a newly formed ocean.Moreover the northern Red Sea region and Gulf of Suez are generally important due totheir hydrocarbon resources. Estimation of higher derivatives of potential fields representsa significant role in geophysical interpretation (qualitative and/or quantitative), as hasbeen demonstrated in many approaches. One of the most popular methods, employinghigher derivatives is the well known Euler deconvolution method. In this method it isvery important to stabilize the derivatives evaluation, because they are very sensitive tonoise and errors in the interpreted field. One way to stabilize higher derivative evaluationis the utilization of the Tikhonov regularization. We show the influence of regularizedderivatives on the properties of the classical 3D Euler deconvolution algorithm and applyit to geophysical potential field data from the Red Sea Rift and its surroundings. Thesolution obtained with regularized derivatives gives better focused depth-estimates, whichare closer to the real position of sources; the results presented here can be used to constraindepth to active crustal structures (boundaries and volcanisms) for northern Red Sea rift.Estimated Euler solution map from Bouguer data utilizing the Tikhonov regularizationreveals both the continental-oceanic crust boundary and several shallow listric normalfaults spreading on the Red Sea margins having NW–SE direction, suggesting NE–SWextension in these regions. Also, generalized depth model for the structure of the Gulfof Aqaba (three pull-apart basins) was well recognized from this map. However, Eulersolutions with band pass filter of magnetic data gives best depth-estimates connectedwith the volcanic intrusive bodies (intense magmatic activity) prevalent on and aroundthe axial trough transform faults resulted from initiation of Red Sea Rift. This depthestimation was derived resulting different structural indexes (SI).

Seismological aspects of the Cairo earthquake, 12th October 1992

On 12 October 1992 a significant earthquake (MB = 5.8) occurred southwest of Cairo in the vicinity of the Dahshour region. For the mainshock, an average moment release M 0 = 9.70E17 n-m; a fault length = 13.8 km; an average displacement = 0.22 m; a stress drop = 0.760 MPa and maximum spectral magnitude = 5.78 were obtained. Spectral magnitude calculations were used in this analysis. The distribution of the well-recorded aftershocks over 15 months using a temporary seismic network installed immediately after the mainshock shows a zone of concentrated activity. Three composite focal mechanism solutions are constructed, using P wave polarity data for 30 earthquakes. These solutions have a mechanism, involving normal and right lateral strike slip motion along E-W to ENE-WSW trending fault plane. The P-wave polarity data of the individual 30 earthquakes are inverted to determine the stress tensor. The stress field estimated is extensional with s3 in the direction of NNE. The stress pattern determined from the inversion is in good agreement with the one estimated from the three composite fault plane solutions, while the neotectonic situation in Northern Egypt supports ENE-WSW extensional movement. However, the region of study has suffered both extensional tectonic activity of the Northern Red Sea rift zone and the compressional tectonic activity along the Hellenic arc. The inconsistency of the principal tension directions may belong to the interaction between the extensional and compressioal tectonics.

Crustal and upper-mantle structure in the Eastern Mediterranean from the analysis of surface wave dispersion curves

SUMMARY The dispersive properties of surface waves are used to infer earth structure in the Eastern Mediterranean region. Using group velocity maps for Rayleigh and Love waves from 7 to 100 s, we invert for the best 1-D crust and upper-mantle structure at a regular series of points. Assembling the results produces a 3-D lithospheric model, along with corresponding maps of sediment and crustal thickness. A comparison of our results to other studies finds the uncertainties of the Moho estimates to be about 5 km. We find thick sediments beneath most of the Eastern Mediterranean basin, in the Hellenic subduction zone and the Cyprus arc. The Ionian Sea is more characteristic of oceanic crust than the rest of the Eastern Mediterranean region as demonstrated, in particular, by the crustal thickness. We also find significant crustal thinning in the Aegean Sea portion of the backarc, particularly towards the south. Notably slower S-wave velocities are found in the upper mantle, especially in the northern Red Sea and Dead Sea Rift, central Turkey, and along the subduction zone. The low velocities in the upper mantle that span from North Africa to Crete, in the Libyan Sea, might be an indication of serpentinized mantle from the subducting African lithosphere. We also find evidence of a strong reverse correlation between sediment and crustal thickness which, while previously demonstrated for extensional regions, also seems applicable for this convergence zone.

Crustal evaluation of the northern Red Sea rift and Gulf of Suez, Egypt from geophysical data: 3-dimensional modeling

Combined 3-D interpretations of gravity and aeromagnetic data have been used in addition to continental and marine seismic profiles, well logs and geological cross-sections. The combination of gravity and magnetic data has improved the geometry and the density distribution in the 3-D calculated profiles. Results of the current work reveal possible crustal thickness and density distribution between the sedimentary cover and the upper mantle including the Moho discontinuity. The Moho depth map of the region, as obtained from the 3-D modeling exhibits various crustal thickness distributions. The type of crust changes gradually from continental to oceanic, from north to south. The zone of crustal thinning coincides mostly with zones of low-density, heated anomalous upper mantle beneath the rift floor (7 km). The eastern plateaus (the Red Sea hills) show by far the largest crustal thickness in the region (32 km). The Moho relief, as indicated from magnetic interpretation, shows a poor flattening especially in the eastern region. This is contrary to what is given by other authors. However, the present results are in good agreement with the geothermal gradient values in the Red Sea. The interpretation of magnetic data of the Red Sea Rift shows that the spreading rate of the part south of latitude 26.5° N agrees well with the theoretical model, in the order of 0.7 cm/yr. Less agreement has been obtained in the part north of latitude 27.5° N. The magnetic anomalies along the axial portion of the rift floor, as deduced from the results of the regional and residual separation and the 3-D magnetic modeling, are mainly caused by the oceanic crustal structures beneath the graben.

Crossing the Waters: Moses and Hamilcar

Previous articleNext article No AccessCrossing the Waters: Moses and HamilcarStanislav SegertStanislav Segert Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Journal of Near Eastern Studies Volume 53, Number 3Jul., 1994 Article DOIhttps://doi.org/10.1086/373691 Views: 8Total views on this site Citations: 2Citations are reported from Crossref Copyright 1994 The University of ChicagoPDF download Crossref reports the following articles citing this article:Neil C Mitchell, Ian C F Stewart The modest seismicity of the northern Red Sea rift, Geophysical Journal International 214, no.33 (May 2018): 1507–1523.https://doi.org/10.1093/gji/ggy176George Karuvelil SCIENCE OF RELIGION AND THEOLOGY: AN EXISTENTIAL APPROACH, Zygon® 47, no.22 (May 2012): 415–437.https://doi.org/10.1111/j.1467-9744.2012.01263.x

Fracture-zone tectonics at Zabargad Island, Red Sea (Egypt)

Zabargad Island, which lies along the western margin of the Red Sea rift, is a remarkable place because it provides fresh exposures of undepleted mantle peridotite. How this peridotite came to be exposed on Zabargad remains unclear. Our field mapping indicates that most of the contacts between peridotite and the adjacent bodies of Pan-African gneiss and Cretaceous(?) Zabargad Formation on the island are now high-angle brittle faults. Zabargad Formation strata have been complexly folded, partly in response to this faulting. Overall, the array of high-angle faults and associated folds on the island resembles those found in cross-rift transfer zones. We suggest, therefore, that the Zabargad fracture zone, a band of submarine escarpments on the floor of the Red Sea north of the island, crosses Zabargad Island and has actively resolved differential movement between the central Red Sea rift and the northern Red Sea rift. The final stage of uplift that brought the unusual peridotite to the earth's surface is related to shallow crustal transpression, which may have inverted an earlier transtensional regime.

Thermal consequences of lithospheric extension: Pure and simple

Simple shear and pure shear extension of the lithosphere produce very different patterns of heat flow and topography. These differences are investigated using a numerical technique which solves for two‐dimensional conductive and advective heat transport through time. Simple shear extension of the lithosphere is modeled as occurring along a straight shear zone. Two parameters define the simple shear model: the dip of the shear zone and its width. Likewise, the pure shear model is defined by two variables: the initial width of a vertical zone of pure shear extension and the rate of change of its width. These pairs of parameters are varied between calculations, as is the overall rate of extension. Each model results in distinct patterns of crustal thinning, lithospheric thermal structure, heat flow, thermal uplift, crustal subsidence, and topography. For the simple shear model, extension results in asymmetric uplift across the rift, while the total volume of uplift is limited by the total amount of extension. The peak heat flow and thermal uplift are centered over the intersection of the shear zone with the surface. Isostatic response to simple shear extension results in successive, formerly active shear zones being rotated into listric faults which sole into a subhorizontal detachment. The pure shear results show that the surface heat flow is greater for smaller widths of the zone of extension. For the same overall extension rate, a pure shear model with a narrow zone of extension can result in pressure release melting of the mantle long before low angle simple shear models. These results are compared with topographic and heat flow data from the northern Red Sea rift, a Neogene continental rift which is close to initiating seafloor spreading. The long wavelength topographic asymmetry across the Red Sea, which has been cited as evidence for simple shear extension of the lithosphere, is not matched by any of the models. The observed high heat flow anomalies in the Red Sea require a large component of pure shear lithospheric extension centered under the region of maximum crustal extension. In contrast, at the plate separation rate of the northern Red Sea, simple shear extension of the lithosphere along a shallow (<30°) dip detachment is ineffective in reproducing the observed heat flow anomalies. Only a narrowing region of pure shear extension can satisfy the width of the rift, and the peak heat flow values and generate pressure release melting.