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The observed geoid height versus Airy's and Pratt's isostatic models using matched asymptotic expansions
KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Geodesi och geoinformatik.
KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Geodesi och geoinformatik.
KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Geodesi och geoinformatik.
2014 (engelsk)Inngår i: Acta Geodaetica et Geophysica, ISSN 2213-5812, Vol. 49, nr 4, s. 473-490Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Isostasy is a key concept in geodesy and geophysics. The classical isostatic models of Airy/Heiskanen and Pratt/Hayford imply that the topographic mass surplus and ocean mass deficit are balanced by mountain roots and anti-roots in the former model and by density variations in the topography and the compensation layer below sea bottom in the latter model. In geophysics gravity inversion is an essential topic where isostasy comes to play. The main objective of this study is to compare the prediction of geoid heights from the above isostatic models based on matched asymptotic expansion with geoid heights observed by the Earth Gravitational Model 2008. Numerical computations were carried out both globally and in several regions, showing poor agreements between the theoretical and observed geoid heights. As an alternative, multiple regression analysis including several non-isostatic terms in addition to the isostatic terms was tested providing only slightly better success rates. Our main conclusion is that the geoid height cannot generally be represented by the simple formulas based on matched asymptotic expansions. This is because (a) both the geoid and isostatic compensation of the topography have regional to global contributions in addition to the pure local signal considered in the classical isostatic models, and (b) geodynamic phenomena are still likely to significantly blur the results despite that all spherical harmonic low-degree (below degree 11) gravity signals were excluded from the study.

sted, utgiver, år, opplag, sider
2014. Vol. 49, nr 4, s. 473-490
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-159122DOI: 10.1007/s40328-014-0064-6ISI: 000346798500007Scopus ID: 2-s2.0-84920280503OAI: oai:DiVA.org:kth-159122DiVA, id: diva2:783827
Merknad

QC 20150127

Tilgjengelig fra: 2015-01-27 Laget: 2015-01-22 Sist oppdatert: 2016-03-17bibliografisk kontrollert
Inngår i avhandling
1. Recovering Moho parameters using gravimetric and seismic data
Åpne denne publikasjonen i ny fane eller vindu >>Recovering Moho parameters using gravimetric and seismic data
2016 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Isostasy is a key concept in geoscience to interpret the state of mass balance between the Earth’s crust and mantle. There are four well-known isostatic models: the classical models of Airy/Heiskanen (A/H), Pratt/Hayford (P/H), and Vening Meinesz (VM) and the modern model of Vening Meinesz-Moritz (VMM). The first three models assume a local and regional isostatic compensation, whereas the latter one supposes a global isostatic compensation scheme.

A more satisfactory test of isostasy is to determine the Moho interface. The Moho discontinuity (or Moho) is the surface, which marks the boundary between the Earth’s crust and upper mantle. Generally, the Moho interface can be mapped accurately by seismic observations, but limited coverage of seismic data and economic considerations make gravimetric or combined gravimetric-seismic methods a more realistic technique for imaging the Moho interface either regional or global scales.

It is the main purpose of this dissertation to investigate an isostatic model with respect to its feasibility to use in recovering the Moho parameters (i.e. Moho depth and Moho density contrast). The study is mostly limited to the VMM model and to the combined approach on regional and global scales. The thesis briefly includes various investigations with the following specific subjects:

1) to investigate the applicability and quality of satellite altimetry data (i.e. marine gravity data) in Moho determination over the oceans using the VMM model, 2) to investigate the need for methodologies using gravimetric data jointly with seismic data (i.e. combined approach) to estimate both the Moho depth and Moho density contrast over regional and global scales, 3) to investigate the spherical terrain correction and its effect on the VMM Moho determination, 4) to investigate the residual isostatic topography (RIT, i.e. difference between actual topography and isostatic topography) and its effect in the VMM Moho estimation, 5) to investigate the application of the lithospheric thermal-pressure correction and its effect on the Moho geometry using the VMM model, 6) Finally, the thesis ends with the application of the classical isostatic models for predicting the geoid height.

The main input data used in the VMM model for a Moho recovery is the gravity anomaly/disturbance corrected for the gravitational contributions of mass density variation due in different layers of the Earth’s crust (i.e. stripping gravity corrections) and for the gravity contribution from deeper masses below the crust (i.e. non-isostatic effects). The corrections are computed using the recent seismic crustal model CRUST1.0.

Our numerical investigations presented in this thesis demonstrate that 1) the VMM approach is applicable for estimating Moho geometry using a global marine gravity field derived by satellite altimetry and that the possible mean dynamic topography in the marine gravity model does not significantly affect the Moho determination, 2) the combined approach could help in filling-in the gaps in the seismic models and it also provides good fit to other global and regional models more than 90 per cent of the locations, 3) despite the fact that the lateral variation of the crustal depth is rather smooth, the terrain affects the Moho result most significantly in many areas, 4) the application of the RIT correction improves the agreement of our Moho result with some published global Moho models, 5) the application of the lithospheric thermal-pressure correction improves the agreement of VMM Moho model with some other global Moho models, 6) the geoid height cannot be successfully represented by the classical models due to many other gravitational signals from various mass variations within the Earth that affects the geoid.  

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2016. s. xi, 56
Serie
TRITA-SOM, ISSN 1653-6126 ; 2016:02
Emneord
crust, gravity, mantle, Moho depth, non-isostatic effect, residual isostatic topography, stripping, thermal state, Vening Meinesz-Moritz model
HSV kategori
Forskningsprogram
Geodesi och geoinformatik
Identifikatorer
urn:nbn:se:kth:diva-183577 (URN)978-91-7595-879-8 (ISBN)
Disputas
2016-04-15, Sal L1, Drottning Kristinas väg 30, KTH, Stockholm, 13:00 (engelsk)
Opponent
Veileder
Merknad

QC 20160317

Tilgjengelig fra: 2016-03-17 Laget: 2016-03-17 Sist oppdatert: 2016-03-17bibliografisk kontrollert

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