scholarly journals Moho density contrast in Antarctica determined by satellite gravity and seismic models

2021 ◽  
Vol 225 (3) ◽  
pp. 1952-1962
Author(s):  
M Abrehdary ◽  
L E Sjöberg
Keyword(s):  
Thick Layer ◽  
Density Contrast ◽  
Mountain Range ◽  
Satellite Gravity ◽  
Crust And Upper Mantle ◽  
Spectral Window ◽  
Isostatic Adjustment ◽  
Vening Meinesz ◽  
Almost All ◽  
Seismic Models

SUMMARY As recovering the crust–mantle/Moho density contrast (MDC) significantly depends on the properties of the Earth's crust and upper mantle, varying from place to place, it is an oversimplification to define a constant standard value for it. It is especially challenging in Antarctica, where almost all the bedrock is covered with a thick layer of ice, and seismic data cannot provide a sufficient spatial resolution for geological and geophysical applications. As an alternative, we determine the MDC in Antarctica and its surrounding seas with a resolution of 1° × 1° by the Vening Meinesz-Moritz gravimetric-isostatic technique using the XGM2019e Earth Gravitational Model and Earth2014 topographic/bathymetric information along with CRUST1.0 and CRUST19 seismic crustal models. The numerical results show that our model, named HVMDC20, varies from 81 kg m−3 in the Pacific Antarctic mid-oceanic ridge to 579 kg m−3 in the Gamburtsev Mountain Range in the central continent with a general average of 403 kg m−3. To assess our computations, we compare our estimates with those of some other gravimetric as well as seismic models (KTH11, GEMMA12C, KTH15C and CRUST1.0), illustrating that our estimates agree fairly well with KTH15C and CRUST1.0 but rather poor with the other models. In addition, we compare the geological signatures with HVMDC20, showing how the main geological structures contribute to the MDC. Finally, we study the remaining glacial isostatic adjustment effect on gravity to figure out how much it affects the MDC recovery, yielding a correlation of the optimum spectral window (7≤ n ≤12) between XGM2019e and W12a GIA models of the order of ∼0.6 contributing within a negligible $ \pm 14$ kg m−3 to the MDC.

scholarly journals On Moho Determination by the Vening Meinesz-Moritz Technique

2021 ◽  
Author(s):  
Lars Erik Sjöberg ◽  
Majid Abrehdary
Keyword(s):  
Least Squares ◽  
Moho Depth ◽  
Glacial Isostatic Adjustment ◽  
Altimetry Data ◽  
Satellite Gravity ◽  
Isostatic Adjustment ◽  
Uncertainty Estimates ◽  
Least Squares Adjustment ◽  
Moho Depths ◽  
Vening Meinesz

This chapter describes a theory and application of satellite gravity and altimetry data for determining Moho constituents (i.e. Moho depth and density contrast) with support from a seismic Moho model in a least-squares adjustment. It presents and applies the Vening Meinesz-Moritz gravimetric-isostatic model in recovering the global Moho features. Internal and external uncertainty estimates are also determined. Special emphasis is devoted to presenting methods for eliminating the so-called non-isostatic effects, i.e. the gravimetric signals from the Earth both below the crust and from partly unknown density variations in the crust and effects due to delayed Glacial Isostatic Adjustment as well as for capturing Moho features not related with isostatic balance. The global means of the computed Moho depths and density contrasts are 23.8±0.05 km and 340.5 ± 0.37 kg/m3, respectively. The two Moho features vary between 7.6 and 70.3 km as well as between 21.0 and 650.0 kg/m3. Validation checks were performed for our modeled crustal depths using a recently published seismic model, yielding an RMS difference of 4 km.

Towards the Moho depth and Moho density contrast along with their uncertainties from seismic and satellite gravity observations

2017 ◽  
Vol 11 (4) ◽  
Author(s):  
M. Abrehdary ◽  
L.E. Sjöberg ◽  
M. Bagherbandi ◽  
D. Sampietro
Keyword(s):  
Inverse Problem ◽  
Density Contrast ◽  
Moho Depth ◽  
Standard Errors ◽  
Combined Method ◽  
Satellite Gravity ◽  
Global Models ◽  
Moho Depths ◽  
Vening Meinesz ◽  
Models Of Gravity

AbstractWe present a combined method for estimating a new global Moho model named KTH15C, containing Moho depth and Moho density contrast (or shortly Moho parameters), from a combination of global models of gravity (GOCO05S), topography (DTM2006) and seismic information (CRUST1.0 and MDN07) to a resolution of 1° × 1° based on a solution of Vening Meinesz-Moritz’ inverse problem of isostasy. This paper also aims modelling of the observation standard errors propagated from the Vening Meinesz-Moritz and CRUST1.0 models in estimating the uncertainty of the final Moho model. The numerical results yield Moho depths ranging from 6.5 to 70.3 km, and the estimated Moho density contrasts ranging from 21 to 650 kg/m

A new Moho depth model for Fennoscandia and surroundings

2020 ◽  
Author(s):  
Majid Abrehdary ◽  
Lars Sjöberg
Keyword(s):  
Seismic Data ◽  
Earth Satellite ◽  
Mean Value ◽  
Crustal Thickening ◽  
Moho Depth ◽  
Gravity Disturbance ◽  
Satellite Gravity ◽  
Value Differences ◽  
Isostatic Adjustment ◽  
Vening Meinesz

<p>Seismic data are the preliminary information for investigating Earth’s interior structure. Since large parts of the world are not yet sufficiently covered by such data, products from Earth satellite gravity and altimetry missions can be used as complimentary for this purpose. This is particularly the case in most of the ocean areas, where seismic data are sparse. One important information of Earth’s interior is the crustal/Moho depth, which is widely mapped from seismic surveys. In this study, we aim at presenting a new Moho depth model from satellite altimetry derived gravity and seismic data in Fennoscandia and its surroundings using the Vening Meinesz-Moritz (VMM) model based on isostatic theory. To that end, the refined Bouguer gravity disturbance (reduced for gravity of topography, density heterogeneities related to bathymetry, ice, sediments, and other crustal components by applying so-called stripping gravity corrections) is corrected for so-called non-isostatic effects (NIEs) of nuisance gravity signals from mass anomalies below the crust due to crustal thickening/thinning, thermal expansion of the mantle, Delayed Glacial Isostatic Adjustment (DGIA) and plate flexure. As Fennoscandia is a key area for GIA research, we particularly investigate the DGIA effect on the gravity disturbance and Moho depth determination from gravity in this area. To do so, the DGIA effect is removed and restored from the NIEs prior to the application of the VMM formula. The numerical results show that the RMS difference of the Moho depth from the (mostly) seismic CRUST1.0 model is 3.6/4.3 km when the above strategy for removing the DGIA effect is/is not applied, respectively. Also, the mean value differences are 0.9 and 1.5 km, respectively. Hence, our study shows that our method of correcting for the DGIA effect on gravity disturbance is significant, resulting in individual changes in Moho depth up to several kilometres.</p>

Contribution of satellite altimetry in modelling Moho density contrast in oceanic areas

2019 ◽  
Vol 13 (1) ◽  
pp. 33-40 ◽  
Author(s):  
M. Abrehdary ◽  
L. E. Sjöberg ◽  
D. Sampietro
Keyword(s):  
Satellite Altimetry ◽  
Density Contrast ◽  
Contrast Model ◽  
Bathymetric Data ◽  
Crustal Model ◽  
Marine Gravity ◽  
Study Results ◽  
Vening Meinesz ◽  
Satellite Altimetry Data

Abstract The determination of the oceanic Moho (or crust-mantle) density contrast derived from seismic acquisitions suffers from severe lack of data in large parts of the oceans, where have not yet been sufficiently covered by such data. In order to overcome this limitation, gravitational field models obtained by means of satellite altimetry missions can be proficiently exploited, as they provide global uniform information with a sufficient accuracy and resolution for such a task. In this article, we estimate a new Moho density contrast model named MDC2018, using the marine gravity field from satellite altimetry in combination with a seismic-based crustal model and Earth’s topographic/bathymetric data. The solution is based on the theory leading to Vening Meinesz-Moritz’s isostatic model. The study results in a high-accuracy Moho density contrast model with a resolution of 1° × 1° in oceanic areas. The numerical investigations show that the estimated density contrast ranges from 14.2 to 599.7 kg/m3 with a global average of 293 kg/m3. In order to evaluate the accuracy of the MDC2018 model, the result was compared with some published global models, revealing that our altimetric model is able to image rather reliable information in most of the oceanic areas. However, the differences between this model and the published results are most notable along the coastal and polar zones, which are most likely due to that the quality and coverage of the satellite altimetry data are worsened in these regions.

scholarly journals Empirical estimation of present-day Antarctic glacial isostatic adjustment and ice mass change

2013 ◽  
Vol 7 (4) ◽  
pp. 3497-3541 ◽  
Author(s):  
B. C. Gunter ◽  
O. Didova ◽  
R. E. M. Riva ◽  
S. R. M. Ligtenberg ◽  
J. T. M. Lenaerts ◽  
...  
Keyword(s):  
Time Frame ◽  
Gravity Models ◽  
Mass Change ◽  
Data Sets ◽  
Glacial Isostatic Adjustment ◽  
Empirical Estimation ◽  
Satellite Gravity ◽  
Amundsen Sea ◽  
Average Value ◽  
Isostatic Adjustment

Abstract. This study explores an approach that simultaneously estimates Antarctic mass balance and glacial isostatic adjustment (GIA) through the combination of satellite gravity and altimetry data sets. The results improve upon previous efforts by incorporating reprocessed data sets over a longer period of time, and now include a firn densification model to account for firn compaction and surface processes. A range of different GRACE gravity models were evaluated, as well as a new ICESat surface height trend map computed using an overlapping footprint approach. When the GIA models created from the combination approach were compared to in-situ GPS ground station displacements, the vertical rates estimated showed consistently better agreement than existing GIA models. In addition, the new empirically derived GIA rates suggest the presence of strong uplift in the Amundsen Sea and Philippi/Denman sectors, as well as subsidence in large parts of East Antarctica. The total GIA mass change estimates for the entire Antarctic ice sheet ranged from 53 to 100 Gt yr−1, depending on the GRACE solution used, and with an estimated uncertainty of ±40 Gt yr−1. Over the time frame February 2003–October 2009, the corresponding ice mass change showed an average value of −100 ± 44 Gt yr−1 (EA: 5 ± 38, WA: −105 ± 22), consistent with other recent estimates in the literature, with the mass loss mostly concentrated in West Antarctica. The refined approach presented in this study shows the contribution that such data combinations can make towards improving estimates of present day GIA and ice mass change, particularly with respect to determining more reliable uncertainties.

Decorrelative Mollifier Gravimetry

2021 ◽  
Author(s):  
Willi Freeden
Keyword(s):  
Inverse Problems ◽  
Density Contrast ◽  
Disturbing Potential ◽  
Book Series ◽  
Inverse Gravimetry ◽  
Constructive Approximation ◽  
Vening Meinesz ◽  
Inverse Gravimetry Problem

<p>The lecture highlights arguments that, coming from multiscale mathematics, have fostered the advancement of gravimetry, as well as those that, generated by gravimetric problems, have contributed to the enhancement in constructive approximation and numerics. Inverse problems in gravimetry are delt with multiscale mollifier decorrelation strategies. Two examples are studied in more detail: (i) Vening Meinesz multiscale surface mollifier regularization to determine locally the Earth's disturbing potential from deflections of vertical, (ii) Newton multiscale volume mollifier regularization of the inverse gravimetry problem to derive locally the density contrast distribution from functionals of the Newton integral and to detect fine particulars of geological relevance. All in all, the Vening Meinesz medal  lecture is meant as an  \lq \lq appetizer'' served to enjoy the tasty meal "Mathematical Geoscience Today'' to be shared by geoscientists and mathematicians in the field of gravimetry. It provides innovative concepts and locally relevant applications presented in a monograph to be published by Birkhäuser in the book series “Geosystems Mathematics” (2021).</p>

scholarly journals CRUST AND UPPER MANTLE IN THE ZONE OF JUNCTION BETWEEN THE CENTRAL ASIAN AND PACIFIC FOLD BELTS

2021 ◽  
Vol 40 (5) ◽  
pp. 16-32
Author(s):  
A.M. Petrishchevsky ◽  
Keyword(s):  
Upper Mantle ◽  
Deep Structure ◽  
Sedimentary Basins ◽  
Density Contrast ◽  
Tectonic Structures ◽  
Crust And Upper Mantle ◽  
North East ◽  
The North ◽  
The Pacific ◽  
Amurian Plate

Spatial distributions of gravity sources and density contrast of geological media, which is reflected by the values of parameter μz , into the crust and upper mantle of Northeast China are analyzed. Features of rheological layering of the tectonosphere and deep spatial relationships of tectonic structures (cratonic blocks, marginal terranes, and sedimentary basins) are defined. In the density contrast distributions the formal signs of Paleozoic subduction of the North-China Craton and Mesozoic subduction of the Pacific Plate under the Amurian Plate were revealed. Crustal deformations are in sharp contrast with upper mantle deformations in structural planes resulting from different directions of tectonic stresses in the Paleozoic and Mesozoic. Thrusting of marginal terranes (Jamusi, Khanka) over the Amurian Plate lithosphere is revealed. Rheology and deep structure of North East China bear many similarities to other regions of the Pacific western margin in Asia and Australia.

scholarly journals As cheias no sul de Portugal em diferentes tipos de bacias hidrográficas

Finisterra ◽  
2012 ◽  
Vol 36 (71) ◽  
Author(s):  
Catarina Ramos ◽  
Eusébio Reis
Keyword(s):  
Flood Frequency ◽  
Rainfall Regime ◽  
Severe Drought ◽  
Mountain Range ◽  
The South ◽  
Drainage Basins ◽  
Cold Pools ◽  
High Flood ◽  
Flooded Area ◽  
Almost All

THE FLOODS IN THE SOUTH OF PORTUGAL IN DIFFERENT KINDS OF DRAINAGEBASINS – The regime of the Portuguese rivers depends on the space and time variation of rainfall. Portugal has clear regional contrasts in the geographical distribution of rainfall. The NW and the Central Mountain Range (Cordilheira Central) are the regions with more rainfall. The NE and the south are the driest regions. Therainfall regime is very irregular. The monthly rainfall regime is clearly Mediterranean with autumn-winter rains (November-March) and an extremely dry summer. The river flows are also very irregular, with severe droughts and surprisingly high flood discharges. These characteristics tend to worsen from NW to SE. The southern rivers have specific discharges 6 to 7 times inferior to the ones of theNW, greater irregularity (the flow in years with more rainfall may surpass 100 to 240 times the flow in driest years), a more severe drought (6 months), almost all are temporary, and flood peaks (200-300 times the average flow) can reach extremely high values.In the twentieth century, floods were responsible for the highest rate of casualties in natural disasters in Portugal, followed by earthquakes: one death for every seven were due to floods. The type of floods known as «progressive floods» mainly affects the big hydrographic basins, such as the River Tagus basin, due to the large flooded area. This kind of flood is caused by heavy rainfall periods connected to the western zonal circulation, which usually lasts several weeks. The dams’ basin system reduces flood frequency, especially in autumn when reservoirs still manage to absorb the highflows after the summer dry period, but cannot «tame» the river. It has even contributed to an increase of the peak flow, as in the 1979 flood. Flashfloods are another kind of floods that occur in Portugal and, unlike the former, are dangerous and deadly, such as those in 1967, 1983 and 1997. They affect the small drainage basins and are caused by heavy and concentrated rainfalls, due to convective depressions (cold pools especially active or depressions caused by the interaction between polar and tropical circulations), namely in the south of the country (Lisbon region, Alentejo and Algarve). In the small drainage basins with a natural regime (uninfluenced by a dam), it is interesting to verify the existence of a trend in these extreme phenomena over the last decades. There has been a clear intensification of flood importance during autumn months, in contrast with an accentuated diminishing in winter and spring months.This trend concerns us mainly for two reasons. Firstly, the rainfall concentration in fewer months lessens its availability in the other months and requires a greater storage capacity. Secondly, this concentration means a bigger rainfall intensity in autumn, with the worsening of the number and intensity of floods and a greater soil loss. Deforestation, soil impermeability, chaotic urbanisation, building on floodplains, the blocking up of small creeks, or their canalisation, the building of walls and transverse embankments along the small creeks courses that work as dikes, contribute to the aggravation of this kind of floods. The floods in rivers of southern Portugal are here analysed, and range from the big drainage basins (River Tagus, 80 100km2), to the smaller ones (Cobres stream, 700 km2; Garganta stream, 1 km2). Also discussed are the human causes that have contributed to increasing the consequences of the floods in small catchments.

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