scholarly journals Density structure and isostasy of the lithosphere in Egypt and their relation to seismicity

2018 ◽  
Author(s):  
Mikhail K. Kaban ◽  
Sami El Khrepy ◽  
Nassir Al-Arifi
Keyword(s):  
Red Sea ◽  
Upper Mantle ◽  
Nile Delta ◽  
Western Desert ◽  
Integrative Model ◽  
Joint Analysis ◽  
Density Structure ◽  
Crust And Upper Mantle ◽  
Gravity Field Model ◽  
Northern Red Sea

Abstract. A joint analysis of the new satellite-terrestrial gravity field model with the recent data on the crustal structure and seismic tomography model was conducted to create an integrative model of the crust and upper mantle; and to investigate the relation of the density structure and the isostatic state of the lithosphere to the seismicity of Egypt. We identified the distinct fragmentation of the lithosphere of Egypt into several blocks. This division is closely related to the seismicity patterns in this region. The relatively dense and strong lithosphere in the Nile Delta limits the seismic activity within this area, while earthquakes are mainly associated with the boundaries of this block. In the same way, the relatively strong lithosphere in the Suez Isthmus and northern Mediterranean prevents the Gulf of Suez from opening further. The central part of Egypt is generally characterized by an increased density of the mantle, which extends to the Mediterranean at a depth of 100 km. This anomaly deepens southward to Gilf El Kebir and eastward to the Eastern Desert. The average density of the crystalline crust is generally reduced in this zone, indicating the increased thickness of the upper crust. The low-density anomaly under the northern Red Sea is limited to 100–125 km, confirming the passive origin of the extension. Most of the earthquakes occur in the crust and uppermost mantle in this structure due to the hot and weak upper mantle underneath. Furthermore, an asymmetric lithosphere structure is observed across the Northern Red Sea. The isostatic anomalies show the fragmentation of the crust of Sinai with the high-density central block. Strong variations of the isostatic anomalies are correlated with the high level of seismicity around Sinai. This tendency is also evident in the North Red Sea, east of the Nile Valley, and in parts of the Western Desert.

scholarly journals Density structure and isostasy of the lithosphere in Egypt and their relation to seismicity

Solid Earth ◽  
2018 ◽  
Vol 9 (4) ◽  
pp. 833-846 ◽  
Author(s):  
Mikhail K. Kaban ◽  
Sami El Khrepy ◽  
Nassir Al-Arifi
Keyword(s):  
Red Sea ◽  
Upper Mantle ◽  
Nile Delta ◽  
Western Desert ◽  
Integrative Model ◽  
Joint Analysis ◽  
Density Structure ◽  
Crust And Upper Mantle ◽  
Gravity Field Model ◽  
Northern Red Sea

Abstract. A joint analysis of the new satellite–terrestrial gravity field model with recent data on the crustal structure and seismic tomography was conducted to create an integrative model of the crust and upper mantle and to investigate the relation of the density structure and the isostatic state of the lithosphere to the seismicity of Egypt. We identified the distinct fragmentation of the lithosphere of Egypt in several blocks. This division is closely related to the seismicity patterns in this region. The relatively dense and strong lithosphere in the Nile Delta limits the seismic activity within this area, while earthquakes are mainly associated with the boundaries of this block. In the same way, the relatively strong lithosphere in the Isthmus of Suez and northern Mediterranean prevents the Gulf of Suez from opening further. The central part of Egypt is generally characterized by an increased density of the mantle, which extends to the Mediterranean at a depth of 100 km. This anomaly deepens southward to Gilf Kebir and eastward to the Eastern Desert. The average density of the crystalline crust is generally reduced in this zone, indicating the increased thickness of the upper crust. The low-density anomaly under the northern Red Sea is limited to 100–125 km, confirming the passive origin of the extension. Most of the earthquakes occur in the crust and uppermost mantle in this structure due to the hot and weak upper mantle underneath. Furthermore, an asymmetric lithosphere structure is observed across the northern Red Sea. The isostatic anomalies show the fragmentation of the crust of Sinai with the high-density central block. Strong variations in the isostatic anomalies are correlated with the high level of seismicity around Sinai. This tendency is also evident in the northern Red Sea, east of the Nile Valley, and in parts of the Western Desert.

scholarly journals Crust and upper mantle resistivity structure in the southwestern end of the Kuril Arc as revealed by the joint analysis of conventional MT and network MT data

2001 ◽  
Vol 53 (8) ◽  
pp. 829-842 ◽  
Author(s):  
Hideyuki Satoh ◽  
Yasunori Nishida ◽  
Yasuo Ogawa ◽  
Masamitsu Takada ◽  
Makoto Uyeshima
Keyword(s):  
Upper Mantle ◽  
Joint Analysis ◽  
Resistivity Structure ◽  
Crust And Upper Mantle

Electrical properties of the lithosphere in the western desert, Egypt, using magnetotelluric sounding

2021 ◽  
Author(s):  
Hossam Marzouk ◽  
Tarek Arafa-Hamed ◽  
Michael Becken ◽  
Mohamed Abdel Zaher ◽  
Matthew Comeau
Keyword(s):  
Upper Mantle ◽  
Seismic Velocity ◽  
Western Desert ◽  
Velocity Data ◽  
Profile Data ◽  
Crust And Upper Mantle ◽  
Near Surface ◽  
The Earth ◽  
Nubian Aquifer ◽  
Dakhla Oasis

<p>We present electrical resistivity models of the crust and upper mantle estimated from 2D inversions of broadband magnetotellurics (MT) data acquired from two profiles in the western desert of Egypt, which can contribute to the understanding of the structural setup of this region. The first profile data are collected from 14 stations along a 250 km profile, in EW direction profile runs along latitude ~25.5°N from Kharga oasis to Dakhla oasis. The second profile comprises 19 stations measured along a 130 km profile in NS direction centered at longitude 28°E and crossing the Farafra. The acquisition for both profiles continued for 1 to 3 days at each station, which allowed for the calculation of impedances for periods from 0.01 sec up to  4096 sec at some sites. The wide frequency band corresponds to a maximal skin depths of up to 150 km that can provide penetration to the top of the asthenosphere. The inversion models display high-conductivity sediments cover at the near surface (<1-2 km), which can be associated with the Nubian aquifer. Along the EW-profile from Kaharge to Dhakla, the crustal basement is overly highly resistive and homogeneous und underlain by a more conductive lithospheric mantle below depths of 30-40 km. Along the N-S profile across Farafra, only the southern portion exhibits a highly resistive crust, whereas beneath Farafra northwards, moderate crustal conductivities are encountered. A comparison has been made between the resultant resistivity models with the 1° tessellated updated crust and lithospheric model of the Earth (LITHO1.0) which was developed by <em>Pasyanos, 2014</em> on the basis of seismic velocity data. The obtained results show a remarkable consistency between the resistivity models and the calculated crustal boundaries. Especially at the Kharga-Dakhla profile a clear matching can be noticed at the upper and lower boundaries of a characteristic anomaly with the Moho and LAB boundaries respectively.</p>

scholarly journals Post-critical SsPmp and its applications to Virtual Deep Seismic Sounding (VDSS) – 2: 1-D imaging of the crust/mantle and joint constraints with receiver functions

2019 ◽  
Vol 219 (2) ◽  
pp. 1334-1347 ◽  
Author(s):  
Tianze Liu ◽  
Simon L Klemperer ◽  
Gabriel Ferragut ◽  
Chunquan Yu
Keyword(s):  
Upper Mantle ◽  
Receiver Functions ◽  
Deep Seismic Sounding ◽  
Moho Depth ◽  
Joint Analysis ◽  
Crust And Upper Mantle ◽  
Slave Craton ◽  
Single Station ◽  
Seismic Sounding ◽  
Novel Method

SUMMARY Virtual Deep Seismic Sounding (VDSS) has emerged as a novel method to image the crust–mantle boundary (CMB) and potentially other lithospheric boundaries. In Part 1, we showed that the arrival time and waveform of post-critical SsPmp, the post-critical reflection phase at the CMB used in VDSS, is sensitive to several different attributes of the crust and upper mantle. Here, we synthesize our methodology of deriving Moho depth, average crustal Vp and uppermost-mantle Vp from single-station observations of post-critical SsPmp under a 1-D assumption. We first verify our method with synthetics and then substantiate it with a case study using the Yellowknife and POLARIS arrays in the Slave Craton, Canada. We show good agreement of crustal and upper-mantle properties derived with VDSS with those given by previous active-source experiments and our own P receiver functions (PRF) in our study area. Finally, we propose a PRF-VDSS joint analysis method to constrain average crustal Vp/Vs ratio and composition. Our PRF-VDSS joint analysis shows that the southwest Slave Craton has an intermediate crustal composition, most consistent with a Mesoarchean age.

Imaging the temperature beneath Ireland and Britain using massive, broadband surface-wave datasets and petrological inversion

2021 ◽  
Author(s):  
Emma L. Chambers ◽  
Raffaele Bonadio ◽  
Sergei Lebedev ◽  
Javier Fullea ◽  
Duygu Kiyan ◽  
...  
Keyword(s):  
Surface Wave ◽  
Phase Velocity ◽  
Upper Mantle ◽  
Thermal Structure ◽  
Surface Elevation ◽  
Joint Analysis ◽  
Crust And Upper Mantle ◽  
Phase Velocities ◽  
Wave Phase ◽  
Optimal Resolution

<p>Deep geothermal resources in low- to medium-temperature settings remain poorly understood and untapped in Ireland and much of Europe. Our new project DIG (De-risking Ireland’s Geothermal Potential) integrates multi-disciplinary, multi-scale datasets in order to investigate Ireland’s low-enthalpy geothermal energy potential. Seismic measurements constrain the distributions of seismic velocities and, through them, the composition and temperature within the lithosphere and underlying mantle. Recent deployments of broadband seismic stations and the surface-wave measurements using the new data yield an unprecedentedly dense data sampling of the crust and upper mantle beneath Ireland and neighbouring Britain. These data form a foundation for the region-scale, multi-parameter modelling of the thermal state of the lithosphere.</p><p>We use the recently assembled dataset of over 11,000 Rayleigh-wave, phase-velocity curves, measured for pairs of stations across Ireland and Britain (Bonadio et al. 2021) and complement it with new interstation measurements of Love-wave phase velocities. The measurements were performed using two methods with complementary period ranges, the teleseismic cross-correlation method and waveform inversion. Spanning a very broad period range (from as short as 4 s to as long as 500 s), the phase velocities provide resolution from the upper-middle crust to the asthenosphere. The joint analysis of Rayleigh and Love measurements constrains the isotropic-average shear-wave velocity, relatable to temperature and composition. The optimal-resolution, phase-velocity maps of Bonadio et al. (2021) for Rayleigh waves and the new maps for Love waves computed in this study provide essential constraints on the thermal structure of the region’s lithosphere. We demonstrate this by inverting the data using an integrated geophysical-petrological thermodynamically self-consistent approach (Fullea et al., 2021). The multi-parameter models produced by the integrated inversions fit the surface-wave and surface-elevation data and reveal the temperatures and geothermal gradients within the crust. </p><p>Bonadio, R., Lebedev, S., Meier, T., Arroucau, P., Schaeffer, A. J., Licciardi, A., Agius, M. R., Horan, C., Collins, L., O'Reilly, B. M., Readman, P. and the Ireland Array Working Group (2021). Optimal resolution tomography with error tracking: imaging the upper mantle beneath Ireland and Britain. <em>Geophys. J. Int., </em>in revision.</p><p>Fullea, J., Lebedev, S., Martinec, Z., & Celli, N. L. (2021). WINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical-petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data. <em>Geophys. J. Int.,</em> revised version under evaluation.</p>

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