In the study of deformations of man-made constructions or in geodynamics one usually needs to car... more In the study of deformations of man-made constructions or in geodynamics one usually needs to carefully monitor fixed objects attached to the deformable body. The purpose is to use precise observat ...
Since the year 2000, some periodic investigations have been performed in the Lilla Edet region to... more Since the year 2000, some periodic investigations have been performed in the Lilla Edet region to monitor and possibly determine the landslide of the area with GPS measurements. The responsible consultant has conducted this project by setting up some stable stations for GPS receivers in the risky areas of Lilla Edet and measured the independent baselines amongst the stations according to their observation plan. Here, we optimise the existing surveying network and determine the optimal configuration of the observation plan based on different criteria.We aim to optimise the current network to become sensitive to detect 5 mm possible displacements in each net point. The network quality criteria of precision, reliability and cost are used as object functions to perform single-, bi- and multi-objective optimisation models. It has been shown in the results that the single-objective model of reliability, which is constrained to the precision, provides much higher precision than the defined...
The incomplete knowledge of the topographic density distribution causes a topographic bias in all... more The incomplete knowledge of the topographic density distribution causes a topographic bias in all gravimetric geoid determinations. This bias becomes critical in aiming for accurate geoid models in high mountainous regions. The bias can be divided into two components: the bias of the Bouguer shell (or Bouguer plate) and that of the remaining terrain. Starting from the known (disturbing) potential at the Earth’s surface, we study the possible location of the bias caused by incomplete reduction of the terrain masses in the computational process, We show that there is no such bias for terrain masses located exterior to the Bouguer plate/shell and/or inside the Bouguer plate at a lateral distance exceeding the height HP of the topography at the computational point. We conclude that the only possible terrain bias could be generated by masses inside a dome of height $$ \left(\sqrt{2}-1\right){H}_P $$ 2 − 1 H P centered along the radius vector through the computational point with its base ...
SUMMARY As recovering the crust–mantle/Moho density contrast (MDC) significantly depends on the p... more 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 gene...
The gravimetric quasigeoid can be determined either directly by Stokes formula or indirectly by c... more The gravimetric quasigeoid can be determined either directly by Stokes formula or indirectly by computing the geoid first and then determining the quasigeoid-to-geoid separation which is then used ...
This chapter describes a theory and application of satellite gravity and altimetry data for deter... more 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 che...
The topographic potential bias at geoid level is the error of the analytically continued geopoten... more The topographic potential bias at geoid level is the error of the analytically continued geopotential from or above the Earth’s surface to the geoid. We show that the topographic potential can be expressed as the sum of two Bouguer shell components, where the density distribution of one is spherical symmetric and the other is harmonic at any point along the normal to a sphere through the computation point. As a harmonic potential does not affect the bias, the resulting topographic bias is that of the first component, i.e. the spherical symmetric Bouguer shell. This implies that the so-called terrain potential is not likely to contribute significantly to the bias. We present three examples of the geoid bias for different topographic density distributions.
Isostasy is a key concept in geoscience in interpreting the state of mass balance between the Ear... more Isostasy is a key concept in geoscience in interpreting the state of mass balance between the Earth’s lithosphere and viscous asthenosphere. A more satisfactory test of isostasy is to determine the depth to and density contrast between crust and mantle at the Moho discontinuity (Moho). Generally, the Moho can be mapped by seismic information, but the limited coverage of such data over large portions of the world (in particular at seas) and economic considerations make a combined gravimetric-seismic method a more realistic approach. The determination of a high-resolution of the Moho constituents for marine areas requires the combination of gravimetric and seismic data to diminish substantially the seismic data gaps. In this study, we estimate the Moho constituents globally for ocean regions to a resolution of 1° × 1° by applying the Vening Meinesz-Moritz method from gravimetric data and combine it with estimates derived from seismic data in a new model named COMHV19. The data files o...
In the study of deformations of man-made constructions or in geodynamics one usually needs to car... more In the study of deformations of man-made constructions or in geodynamics one usually needs to carefully monitor fixed objects attached to the deformable body. The purpose is to use precise observat ...
Since the year 2000, some periodic investigations have been performed in the Lilla Edet region to... more Since the year 2000, some periodic investigations have been performed in the Lilla Edet region to monitor and possibly determine the landslide of the area with GPS measurements. The responsible consultant has conducted this project by setting up some stable stations for GPS receivers in the risky areas of Lilla Edet and measured the independent baselines amongst the stations according to their observation plan. Here, we optimise the existing surveying network and determine the optimal configuration of the observation plan based on different criteria.We aim to optimise the current network to become sensitive to detect 5 mm possible displacements in each net point. The network quality criteria of precision, reliability and cost are used as object functions to perform single-, bi- and multi-objective optimisation models. It has been shown in the results that the single-objective model of reliability, which is constrained to the precision, provides much higher precision than the defined...
The incomplete knowledge of the topographic density distribution causes a topographic bias in all... more The incomplete knowledge of the topographic density distribution causes a topographic bias in all gravimetric geoid determinations. This bias becomes critical in aiming for accurate geoid models in high mountainous regions. The bias can be divided into two components: the bias of the Bouguer shell (or Bouguer plate) and that of the remaining terrain. Starting from the known (disturbing) potential at the Earth’s surface, we study the possible location of the bias caused by incomplete reduction of the terrain masses in the computational process, We show that there is no such bias for terrain masses located exterior to the Bouguer plate/shell and/or inside the Bouguer plate at a lateral distance exceeding the height HP of the topography at the computational point. We conclude that the only possible terrain bias could be generated by masses inside a dome of height $$ \left(\sqrt{2}-1\right){H}_P $$ 2 − 1 H P centered along the radius vector through the computational point with its base ...
SUMMARY As recovering the crust–mantle/Moho density contrast (MDC) significantly depends on the p... more 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 gene...
The gravimetric quasigeoid can be determined either directly by Stokes formula or indirectly by c... more The gravimetric quasigeoid can be determined either directly by Stokes formula or indirectly by computing the geoid first and then determining the quasigeoid-to-geoid separation which is then used ...
This chapter describes a theory and application of satellite gravity and altimetry data for deter... more 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 che...
The topographic potential bias at geoid level is the error of the analytically continued geopoten... more The topographic potential bias at geoid level is the error of the analytically continued geopotential from or above the Earth’s surface to the geoid. We show that the topographic potential can be expressed as the sum of two Bouguer shell components, where the density distribution of one is spherical symmetric and the other is harmonic at any point along the normal to a sphere through the computation point. As a harmonic potential does not affect the bias, the resulting topographic bias is that of the first component, i.e. the spherical symmetric Bouguer shell. This implies that the so-called terrain potential is not likely to contribute significantly to the bias. We present three examples of the geoid bias for different topographic density distributions.
Isostasy is a key concept in geoscience in interpreting the state of mass balance between the Ear... more Isostasy is a key concept in geoscience in interpreting the state of mass balance between the Earth’s lithosphere and viscous asthenosphere. A more satisfactory test of isostasy is to determine the depth to and density contrast between crust and mantle at the Moho discontinuity (Moho). Generally, the Moho can be mapped by seismic information, but the limited coverage of such data over large portions of the world (in particular at seas) and economic considerations make a combined gravimetric-seismic method a more realistic approach. The determination of a high-resolution of the Moho constituents for marine areas requires the combination of gravimetric and seismic data to diminish substantially the seismic data gaps. In this study, we estimate the Moho constituents globally for ocean regions to a resolution of 1° × 1° by applying the Vening Meinesz-Moritz method from gravimetric data and combine it with estimates derived from seismic data in a new model named COMHV19. The data files o...
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Papers by Lars Sjöberg