scholarly journals How isostasy explains continental rifting in East Africa?

2020 ◽  
Author(s):  
Mohammad Bagherbandi ◽  
Nureldin A. A. Gido
Keyword(s):  
East Africa ◽  
Rift Valley ◽  
Plate Tectonics ◽  
Gravity Data ◽  
Density Contrast ◽  
Earthquake Activity ◽  
Continental Rifting ◽  
The Earth ◽  
Geodynamic Processes ◽  
Thin Crust

<p>The principle of isostasy plays an important role to understand the relation between different geodynamic processes. Although, it is difficult to find an exact method that delivers a complete image of the Earth structure. However, gravimetric methods are alternative to provide images of the interior of the Earth. The Earth’s crust parameters, i.e. crustal depth and crust-mantle density contrast, can reveal adequate information about the solid Earth system such as volcanic activity, earthquake and continental rifting. Hence, in this study, a combine Moho model using seismic and gravity data is determined to investigate the relationship between the isostatic state of the lithosphere and seismic activities in East Africa. Our results show that isostatic equilibrium and compensation states are closely correlated to the seismicity patterns in the study area. For example, several studies suggest that African superplume causes the rift valley, and consequently differences in crustal and mantle densities occur. This paper presents a method to determine the crustal thickness and crust-mantle density contrast and consequently one can observe low-density contrast (about 200 kg/m<sup>3</sup> ) and thin crust (about 30 km) near the triple junction plate tectonics in East Africa (Afar Triangle), which confirms the state of overcompensation in the rift valley areas. Furthermore, the density structure of the lithosphere shows a large correlation with the earthquake activity, sub-crustal stress and volcanic distribution across East Africa.</p>

Unraveling the upper mantle heterogeneity from integrated multi-observable inversions

2020 ◽  
Author(s):  
Javier Fullea ◽  
Sergei Lebedev ◽  
Zdenek Martinec ◽  
Nicolas Celli
Keyword(s):  
Seismic Tomography ◽  
Upper Mantle ◽  
Plate Tectonics ◽  
Seismic Velocity ◽  
Gravity Data ◽  
Density Field ◽  
Seismic Velocities ◽  
Satellite Gravity ◽  
The Earth ◽  
Multiple Data Sets

<p>The lateral and vertical thermochemical heterogeneity in the mantle is a long standing question in geodynamics. The forces that control mantle flow and therefore Plate Tectonics arise from the density and viscosity lateral and vertical variations. A common approach to estimate the density field for geodynamical purposes is to simply convert seismic tomography anomalies sometimes assuming constraints from mineral physics. Such converted density field does not match in general with the observed gravity field, typically predicting anomalies the amplitudes of which are too large. Knowledge on the lateral variations in lithospheric density is essential to understand the dynamic/residual isostatic components of the Earth’s topography linking deep and surface processes. The cooling of oceanic lithosphere, the bathymetry of mid oceanic ridges, the buoyancy and stability of continental cratons or the thermochemical structure of mantle plumes are all features central to Plate Tectonics that are dramatically related to mantle temperature and composition.</p><p><br>Conventional methods of seismic tomography, topography and gravity data analysis constrain distributions of seismic velocity and density at depth, all depending on temperature and composition of the rocks within the Earth. However, modelling and interpretation of multiple data sets provide a multifaceted image of the true thermochemical structure of the Earth that needs to be appropriately and consistently integrated. A simple combination of gravity, petrological and seismic models alone is insufficient due to the non-uniqueness and different sensitivities of these models, and the internal consistency relationships that must connect all the intermediate parameters describing the Earth involved. In fact, global Earth models based on different observables often lead to rather different, even contradictory images of the Earth.</p><p><br> Here we present a new global thermochemical model of the lithosphere-upper mantle (WINTERC-grav) constrained by state-of-the-art global waveform tomography, satellite gravity (geoid and gravity anomalies and gradiometric measurements from ESA's GOCE mission), surface elevation and heat flow data. WINTERC-grav is based upon an integrated geophysical-petrological approach where all relevant rock physical properties modelled (seismic velocities and density) are computed within a thermodynamically self-consistent framework allowing for a direct parameterization of the temperature and composition variables.</p>

Understanding the Earth: the contribution of Marie Tharp

2020 ◽  
pp. SP506-2019-248
Author(s):  
Bettie Matheson Higgs
Keyword(s):  
Atlantic Ocean ◽  
Rift Valley ◽  
Plate Tectonics ◽  
East African Rift ◽  
Ocean Floor ◽  
Columbia University ◽  
East African ◽  
The Earth ◽  
History Of ◽  
African Rift

AbstractMarie Tharp worked all her life as a geoscientist, and for the most part for the recognition and benefit of her male colleagues. She was employed to assist researchers at Columbia University. Her male colleagues readily used her ingenuity and insights without giving her recognition. Marie tolerated this at first but eventually began to ask for recognition for her own work. Her most influential work was the production of physiographical maps of the ocean floor. During this work, in the 1950s, Marie was the first scientist to realize that there was a large rift running the length of the Atlantic Ocean, and she eventually demonstrated that this rift linked to the East African Rift Valley. Her male colleagues suppressed this discovery for reasons of their own, and 4 years later presented it as their own research. The work caused some key figures in the history of plate tectonics to change the direction of their research. Marie suffered in her career due to rivalries between her male colleagues. It was not until the 1990s that Marie began to be recognized nationally and internationally, and receive awards for her work.

PLANETARY SELF-ORGANIZATION

2020 ◽  
Vol 42 (3) ◽  
pp. 271-282
Author(s):  
OLEG IVANOV
Keyword(s):  
Dynamical System ◽  
Heat Source ◽  
Mantle Convection ◽  
Plate Tectonics ◽  
Rotation Speed ◽  
Self Organization ◽  
Heat Sources ◽  
Kinematic Parameters ◽  
The Earth ◽  
New Type

The general characteristics of planetary systems are described. Well-known heat sources of evolution are considered. A new type of heat source, variations of kinematic parameters in a dynamical system, is proposed. The inconsistency of the perovskite-post-perovskite heat model is proved. Calculations of inertia moments relative to the D boundary on the Earth are given. The 9 times difference allows us to claim that the sliding of the upper layers at the Earth's rotation speed variations emit heat by viscous friction.This heat is the basis of mantle convection and lithospheric plate tectonics.

scholarly journals Revolutions in the earth sciences

1999 ◽  
Vol 354 (1392) ◽  
pp. 1915-1919 ◽  
Author(s):  
Claude Allègre ◽  
Vincent Courtillot
Keyword(s):  
Earth Sciences ◽  
Quantum Mechanics ◽  
20Th Century ◽  
Plate Tectonics ◽  
Statistical Physics ◽  
Natural Sciences ◽  
Scientific Revolutions ◽  
The Earth

The 20th century has been a century of scientific revolutions for many disciplines: quantum mechanics in physics, the atomic approach in chemistry, the nonlinear revolution in mathematics, the introduction of statistical physics. The major breakthroughs in these disciplines had all occurred by about 1930. In contrast, the revolutions in the so–called natural sciences, that is in the earth sciences and in biology, waited until the last half of the century. These revolutions were indeed late, but they were no less deep and drastic, and they occurred quite suddenly. Actually, one can say that not one but three revolutions occurred in the earth sciences: in plate tectonics, planetology and the environment. They occurred essentially independently from each other, but as time passed, their effects developed, amplified and started interacting. These effects continue strongly to this day.

Mapping Mean Lake Surface from satellite altimetry and GPS kinematic surveys

2021 ◽  
Author(s):  
Jean-Francois Crétaux ◽  
Muriel Berge-Nguyen ◽  
Stephane Calmant ◽  
Sara Fleury ◽  
Rysbek Satylkanov ◽  
...  
Keyword(s):  
Lake Water ◽  
Short Wavelength ◽  
Satellite Altimetry ◽  
Gravity Data ◽  
Validation Dataset ◽  
Large Set ◽  
Lake Surface ◽  
Laser Altimetry ◽  
Geoid Model ◽  
The Earth

<p>Lake water height is a key variable in water cycle and climate change studies, which is achievable using satellite altimetry constellation. A method based on data processing of altimetry from several satellites has been developed to interpolate mean lake surface (MLS) over a set of 22 big lakes distributed on the Earth. It has been applied on nadir radar altimeters in Low Resolution Mode (LRM: Jason-3, Saral/AltiKa, CryoSat-2) in Synthetic Aperture Radar (SAR) mode (Sentinel-3A), and in SAR interferometric (SARin) mode (CryoSat-2), and on laser altimetry (ICESat). Validation of the method has been performed using a set of kinematic GPS height profiles from 18 field campaigns over the lake Issykkul, by comparison of altimetry’s height at crossover points for the other lakes and using the laser altimetry on ICESat-2 mission. The precision reached ranges from 3 to 7 cm RMS (Root Mean Square) depending on the lakes. Currently, lake water level inferred from satellite altimetry is provided with respect to an ellipsoid. Ellipsoidal heights are converted into orthométric heights using geoid models interpolated along the satellite tracks. These global geoid models were inferred from geodetic satellite missions coupled with absolute and regional anomaly gravity data sets spread over the Earth. However, the spatial resolution of the current geoid models does not allow capturing short wavelength undulations that may reach decimeters in mountaineering regions or for rift lakes (Baikal, Issykkul, Malawi, Tanganika). We interpolate in this work the geoid height anomalies with three recent geoid models, the EGM2008, XGM2016 and EIGEN-6C4d, and compare them with the Mean Surface of 22 lakes calculated using satellite altimetry. Assuming that MLS mimics the local undulations of the geoid, our study shows that over a large set of lakes (in East Africa, Andean mountain and Central Asia), short wavelength undulations of the geoid in poorly sampled areas can be derived using satellite altimetry. The models used in this study present very similar geographical patterns when compared to MLS. The precision of the models largely depends on the location of the lakes and is about 18 cm, in average over the Earth. MLS can serve as a validation dataset for any future geoid model. It will also be useful for validation of the future mission SWOT (Surface Water and Ocean Topography) which will measure and map water heights over the lakes with a high horizontal resolution of 250 by 250 meters.</p>

Analysis of the Topography and Gravity Data for the Earth-like Venus

2021 ◽  
Vol 55 (1) ◽  
pp. 11-19
Author(s):  
T. I. Menshchikova ◽  
T. V. Gudkova ◽  
V. N. Zharkov
Keyword(s):  
Gravity Data ◽  
The Earth

scholarly journals Geometrical Characterisation of the Mamfe Basin, Cameroon, from the Earth, Gravitational Model (EGM 2008)

2018 ◽  
Vol 7 (1) ◽  
pp. 94
Author(s):  
Anatole Eugene Djieto Lordon ◽  
Mbohlieu YOSSA ◽  
Christopher M Agyingi ◽  
Yves Shandini ◽  
Thierry Stephane Kuisseu
Keyword(s):  
Average Length ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Igneous Rocks ◽  
Average Depth ◽  
The Earth ◽  
Gravitational Model ◽  
Petroleum Generation ◽  
Anomaly Map ◽  
Bouguer Anomaly Map

Gravimetric studies using the ETOPO1-corrected high resolution satellite-based EGM2008 gravity data was used to define the surface extent, depth to basement and shape of the Mamfe basin. The Bouguer anomaly map was produced in Surfer 11.0. The Fast Fourier Transformed data was analyzed by spectral analysis to remove the effect of the regional bodies in the study area. The residual anomaly map obtained was compared with the known geology of the study area, and this showed that the gravity highs correspond to the metamorphic and igneous rocks while the gravity lows match with Cretaceous sediments. Three profiles were drawn on the residual anomaly map along which 2D models of the Mamfe basin were drawn. The modeling was completed in Grav2dc v2.06 software which uses the Talwini’s algorithm and the resulting models gave the depth to basement and the shape of the basement along the profiles. After processing and interpretation, it was deduced that the Mamfe basin has an average length and width of 77.6 km and 29.2 km respectively, an average depth to basement of 5 km and an overall U-shape basement. These dimensions (especially the depth) theoretically create the depth and temperature conditions for petroleum generation. 

scholarly journals Prolific Lightning and Thunderstorm Initiation over the Lake Victoria Basin in East Africa

2020 ◽  
Vol 148 (5) ◽  
pp. 1971-1985 ◽  
Author(s):  
Katrina S. Virts ◽  
Steven J. Goodman
Keyword(s):  
East Africa ◽  
Hot Spots ◽  
Seasonal Cycle ◽  
Lake Victoria ◽  
Intertropical Convergence Zone ◽  
Lake Victoria Basin ◽  
The Earth ◽  
Total Lightning ◽  
Average Cluster

Abstract The Lake Victoria basin of East Africa is home to over 30 million people, over 200 000 of whom are employed in fishing or transportation on the lake. Approximately 3000–5000 individuals are killed by thunderstorms yearly, primarily by outflow winds and resulting large waves. Prolific lightning activity and thunderstorm initiation in the basin are examined using continuous total lightning observations from the Earth Networks Global Lightning Network (ENGLN) for September 2014–August 2018. Seasonal shifts in the intertropical convergence zone produce semiannual lightning maxima over the lake. Diurnally, solar heating and lake and valley breezes produce daytime lightning maxima north and east of the lake, while at night the peak lightning density propagates southwestward across the lake. Cluster analysis reveals terrain-related thunderstorm initiation hot spots northeast of the lake; clusters also initiate over the lake and northern lowlands. The most prolific clusters initiate between 1100 and 1400 LT, about 1–2 h earlier than the average cluster. Most daytime thunderstorms dissipate without reaching Lake Victoria, and annually 85% of clusters producing over 1000 flashes over Lake Victoria initiate in situ. Initiation times of prolific Lake Victoria clusters exhibit a bimodal seasonal cycle: equinox-season thunderstorms initiate most frequently between 2200 and 0400 LT, while solstice-season thunderstorms initiate most frequently from 0500 to 0800 LT, more than 12 h after the afternoon convective peak over land. More extreme clusters are more likely to have formed over land and propagated over the lake, including 36 of the 100 most extreme Lake Victoria thunderstorms. These mesoscale clusters are most common during February–April and October–November.

scholarly journals Accuracy Analysis of Gravity Field Changes from Grace RL06 and RL05 Data Compared to in Situ Gravimetric Measurements in the Context of Choosing Optimal Filtering Type

2020 ◽  
Vol 55 (3) ◽  
pp. 100-117
Author(s):  
Viktor Szabó ◽  
Dorota Marjańska
Keyword(s):  
Gravity Field ◽  
Ocean Circulation ◽  
Gravity Data ◽  
The Other ◽  
Subsurface Water ◽  
Satellite Gravity ◽  
Absolute Gravimetry ◽  
The Earth ◽  
Gravity Measurements ◽  
Gravity Recovery

AbstractGlobal satellite gravity measurements provide unique information regarding gravity field distribution and its variability on the Earth. The main cause of gravity changes is the mass transportation within the Earth, appearing as, e.g. dynamic fluctuations in hydrology, glaciology, oceanology, meteorology and the lithosphere. This phenomenon has become more comprehensible thanks to the dedicated gravimetric missions such as Gravity Recovery and Climate Experiment (GRACE), Challenging Minisatellite Payload (CHAMP) and Gravity Field and Steady-State Ocean Circulation Explorer (GOCE). From among these missions, GRACE seems to be the most dominating source of gravity data, sharing a unique set of observations from over 15 years. The results of this experiment are often of interest to geodesists and geophysicists due to its high compatibility with the other methods of gravity measurements, especially absolute gravimetry. Direct validation of gravity field solutions is crucial as it can provide conclusions concerning forecasts of subsurface water changes. The aim of this work is to present the issue of selection of filtration parameters for monthly gravity field solutions in RL06 and RL05 releases and then to compare them to a time series of absolute gravimetric data conducted in quasi-monthly measurements in Astro-Geodetic Observatory in Józefosław (Poland). The other purpose of this study is to estimate the accuracy of GRACE temporal solutions in comparison with absolute terrestrial gravimetry data and making an attempt to indicate the significance of differences between solutions using various types of filtration (DDK, Gaussian) from selected research centres.

scholarly journals Transition from continental rifting to oceanic spreading in the northern Red Sea area

2021 ◽  
Author(s):  
Sami El Khrepy ◽  
Ivan Koulakov ◽  
Nassir Al-Arifi ◽  
Mamdouh S. Alajmi ◽  
Ayman N. Qadrouh
Keyword(s):  
Red Sea ◽  
Plate Tectonics ◽  
Continental Rifting ◽  
Low Velocity ◽  
Lower Velocity ◽  
Velocity Anomaly ◽  
Oceanic Spreading ◽  
Lithospheric Extension ◽  
Sea Area ◽  
Northern Red Sea

<p><strong>Lithosphere extension, which plays an essential role in plate tectonics, occurs both in continents (as rift systems) and oceans (spreading along mid-oceanic ridges). The northern Red Sea area is a unique natural geodynamic laboratory, where the ongoing transition from continental rifting to oceanic spreading can be observed. Here, we analyze travel time data from a merged catalogue provided by the Egyptian and Saudi Arabian seismic networks to build a three-dimensional model of seismic velocities in the crust and uppermost mantle beneath the northern Red Sea and surroundings. The derived structures clearly reveal a high-velocity anomaly coinciding with the Red Sea basin and a narrow low-velocity anomaly centered along the rift axis. We interpret these structures as a transition of lithospheric extension from continental rifting to oceanic spreading. The transitional lithosphere is manifested by a dominantly positive seismic anomaly indicating the presence of a 50–70-km-thick and 200–300-km-wide cold lithosphere. Along the forming oceanic ridge axis, an elongated low-velocity anomaly marks a narrow localized nascent spreading zone that disrupts the transitional lithosphere. Along the eastern margins of the Red Sea, the lithosphere is disturbed by the lower-velocity anomalies coinciding with areas of basaltic magmatism.</strong></p>

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