Gävle, Sweden
Gävle, Sweden

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Kierulf H.P.,Geodetic Institute | Kierulf H.P.,University of Oslo | Steffen H.,Lantmateriet | Simpson M.J.R.,Geodetic Institute | And 3 more authors.
Journal of Geophysical Research B: Solid Earth | Year: 2014

In Fennoscandia, the process of Glacial Isostatic Adjustment (GIA) drives ongoing crustal deformation. Crustal velocities from GPS observations have proved to be a useful tool in constraining GIA models. However, reference frame uncertainties, plate tectonics, intraplate deformations as well as other geophysical processes contaminate the results. Former studies have shown that different International Terrestrial Reference Frames have large discrepancies, especially in the vertical component, which hamper geophysical interpretation. We present new velocity estimates for the Fennoscandian and North European GPS network. Our GPS velocity field is directly realized in a GIA reference frame. Using this method (named the GIA frame approach) we are able to constrain GIA models with minimal influence of errors in the reference frame or biasing signals from plate tectonics. The drawbacks are more degrees of freedom that might mask real but unmodeled signals. Monte Carlo tests suggest that our approach is robust at the 97% level in terms of correctly separating different models of ice history but, depending on deformation patterns, the identified Earth model may be slightly biased in up to 39% of cases. We compare our results to different one- and three-dimensional GIA models employing different global ice-load histories. The GIA models generally provide good fit to the data but there are still significant discrepancies in some areas. We suggest that these differences are mainly related to inaccuracies in the ice models and/or lateral inhomogeneities in the Earth structure under Fennoscandia. Thus, GIA models still need to be improved, but the GIA frame approach provides a base for further improvements. © 2014. American Geophysical Union.

Paulsson J.,KTH Royal Institute of Technology | Paasch J.M.,Lantmateriet
Land Use Policy | Year: 2015

The international standard for land administration, LADM, ISO 19152, has been the subject of numerous research activities during the last one and a half decade, with topics ranging from technical implementation issues and the registration of real property to legal and organisational aspects. However, some areas have been more researched than others. The aim of this study is to provide an overview of the research as evidenced by research publications 2001-2015 to discuss the distribution of interest areas within LADM research. In total 184 publications on LADM have been analysed in the study. The result shows that technical and real property registration issues have been in focus throughout the surveyed period, whereas there has been less focus on research on legal and organisational matters. There has, however, in recent years been an slight increase in legal research, whereas research on organisational matters, such as efficiency and how to organise and manage interests in land and the benefits and costs for implementing the standard, still is lacking in comparison with the other investigated fields of research, and should be an important area to research now during the implementation phase of LADM. © 2015 Elsevier Ltd.

Hedenas H.,Royal Swedish Academy Of Sciences | Olsson H.,Swedish University of Agricultural Sciences | Jonasson C.,Royal Swedish Academy Of Sciences | Bergstedt J.,Linköping University | And 3 more authors.
Ambio | Year: 2011

This study was conducted in the Swedish sub-Arctic, near Abisko, in order to assess the direction and scale of possible vegetation changes in the alpinebirch forest ecotone. We have re-surveyed shrub, tree and vegetation data at 549 plots grouped into 61 clusters. The plots were originally surveyed in 1997 and re-surveyed in 2010. Our study is unique for the area as we have quantitatively estimated a 19% increase in tree biomass mainly within the existing birch forest. We also found significant increases in the cover of two vegetation types - "birch forest-heath with mosses" and "meadow with low herbs", while the cover of snowbed vegetation decreased significantly. The vegetation changes might be caused by climate, herbivory and past human impact but irrespective of the causes, the observed transition of the vegetation will have substantial effects on the mountain ecosystems. © Royal Swedish Academy of Sciences 2011.

Vey S.,Leibniz University of Hanover | Steffen H.,Lantmateriet | Muller J.,Leibniz University of Hanover | Boike J.,Alfred Wegener Institute for Polar and Marine Research
Journal of Geodesy | Year: 2013

Our study analyses satellite and land-based observations of the Yakutsk region centred at the Lena watershed, an area characterised mainly by continuous permafrost. Using monthly solutions of the Gravity Recovery And Climate Experiment satellite mission, we detect a mass increase over central Siberia from 2002 to 2007 which reverses into a mass decrease between 2007 and 2011. No significant mass trend is visible for the whole observation period. To further quantify this behaviour, different mass signal components are studied in detail: (1) inter-annual variation in the atmospheric mass, (2) a possible effect of glacial isostatic adjustment (GIA), and (3) hydrological mass variations. In standard processing the atmospheric mass signal is reduced based on the data from numerical weather prediction models. We use surface pressure observations in order to validate this atmospheric reduction. On inter-annual time scale the difference between the atmospheric mass signal from model prediction and from surface pressure observation is <4 mm in equivalent water height. The effect of GIA on the mass signal over Siberia is calculated using a global ice model and a spherically symmetric, compressible, Maxwell-viscoelastic earth model. The calculation shows that for the investigated area any effect of GIA can be ruled out. Hence, the main part of the signal can be attributed to hydrological mass variations. We briefly discuss potential hydrological effects such as changes in precipitation, river discharge, surface and subsurface water storage. © 2012 Springer-Verlag Berlin Heidelberg.

Brandes C.,Leibniz University of Hanover | Steffen H.,Lantmateriet | Steffen R.,Uppsala University | Wu P.,University of Hong Kong
Geology | Year: 2015

There is growing evidence that climate-induced melting of large ice sheets has been able to trigger fault reactivation and earthquakes around the migrating ice limit. Even today, the stress due to glacial isostatic adjustment can continue to induce seismicity within the onceglaciated region. Northern Central Europe lies outside the former ice margin and is regarded as a low-seismicity area. However, several historic earthquakes with intensities of up to VII occurred in this region during the past 1200 years. Here we show with numerical simulations that the seismicity can potentially be explained by the decay of the Scandinavian ice sheet after the Weichselian glaciation. Combination of historic earthquake epicenters with fault maps relates historic seismicity to major reverse faults of Late Cretaceous age. Mesozoic normal faults remained inactive in historic times. We suggest that many faults in northern Central Europe are active during postglacial times. This is a novelty that sheds new light on the distribution of postglacial faulting and seismicity. In addition, we present the first consistent model that can explain both the occurrence of deglaciation seismicity and the historic earthquakes in northern Central Europe. © 2015 Geological Society of America.

Steffen H.,Lantmateriet | Wu P.,University of Hong Kong
Solid Earth | Year: 2014

The sensitivity of global navigation satellite system (GNSS) measurements in Fennoscandia to nearby viscosity variations in the upper mantle is investigated using a 3-D finite element model of glacial isostatic adjustment (GIA). Based on the lateral viscosity structure inferred from seismic tomography and the location of the ice margin at the last glacial maximum (LGM), the GIA earth model is subdivided into four layers, where each of them contains an amalgamation of about 20 blocks of different shapes in the central area. The sensitivity kernels of the three velocity components at 10 selected GNSS stations are then computed for all the blocks. We find that GNSS stations within the formerly glaciated area are most sensitive to mantle viscosities below and in its near proximity, i.e., within about 250 km in general. However, this can be as large as 1000 km if the stations lie near the center of uplift. The sensitivity of all stations to regions outside the ice margin during the LGM is generally negligible. In addition, it is shown that prominent structures in the second (250-450 km depth) and third layers (450-550 km depth) of the upper mantle may be readily detected by GNSS measurements, while the viscosity in the first mantle layer below the lithosphere (70-250 km depth) along the Norwegian coast, which is related to lateral lithospheric thickness variation there, can also be detected but with limited sensitivity. For future investigations on the lateral viscosity structure, preference should be on GNSS stations within the LGM ice margin. But these stations can be grouped into clusters to improve the inference of viscosity in a specific area. However, the GNSS measurements used in such inversion should be weighted according to their sensitivity. Such weighting should also be applied when they are used in combination with other GIA data (e.g., relative sea-level and gravity data) for the inference of mantle viscosity. © Author(s) 2014. CC Attribution 3.0 License.

Steffen H.,Lantmateriet | Wu P.,University of Calgary | Wu P.,University of Hong Kong | Wang H.,CAS Wuhan Institute of Geodesy and Geophysics
Solid Earth | Year: 2014

Fréchet (sensitivity) kernels are an important tool in glacial isostatic adjustment (GIA) investigations to understand lithospheric thickness, mantle viscosity and ice-load model variations. These parameters influence the interpretation of geologic, geophysical and geodetic data, which contribute to our understanding of global change.

We discuss global sensitivities of relative sea-level (RSL) data of the last 18 000 years. This also includes indicative RSL-like data (e.g., lake levels) on the continents far off the coasts. We present detailed sensitivity maps for four parameters important in GIA investigations (ice-load history, lithospheric thickness, background viscosity, lateral viscosity variations) for up to nine dedicated times. Assuming an accuracy of 2 m of RSL data of all ages (based on analysis of currently available data), we highlight areas around the world where, if the environmental conditions allowed its deposition and survival until today, RSL data of at least this accuracy may help to quantify the GIA modeling parameters above.

The sensitivity to ice-load history variations is the dominating pattern covering almost the whole world before about 13 ka (calendar years before 1950). The other three parameters show distinct patterns, but are almost everywhere overlapped by the ice-load history pattern. The more recent the data are, the smaller the area of possible RSL locations that could provide enough information to a parameter. Such an area is mainly limited to the area of former glaciation, but we also note that when the accuracy of RSL data can be improved, e.g., from 2 m to 1 m, these areas become larger, allowing better inference of background viscosity and lateral heterogeneity. Although the patterns depend on the chosen models and error limit, our results are indicative enough to outline areas where one should look for helpful RSL data of a certain time period. Our results also indicate that as long as the ice-load history is not sufficiently known, the inference of lateral heterogeneities in mantle viscosity or lithospheric thickness will be interfered by the uncertainty of the ice model. © Author(s) 2014. CC Attribution 3.0 License.

Steffen H.,Lantmateriet | Kaufmann G.,Free University of Berlin | Lampe R.,University of Greifswald
Solid Earth | Year: 2014

During the last glacial maximum, a large ice sheet covered Scandinavia, which depressed the earth's surface by several 100 m. In northern central Europe, mass redistribution in the upper mantle led to the development of a peripheral bulge. It has been subsiding since the begin of deglaciation due to the viscoelastic behaviour of the mantle. We analyse relative sea-level (RSL) data of southern Sweden, Denmark, Germany, Poland and Lithuania to determine the lithospheric thickness and radial mantle viscosity structure for distinct regional RSL subsets. We load a 1-D Maxwell-viscoelastic earth model with a global ice-load history model of the last glaciation. We test two commonly used ice histories, RSES from the Australian National University and ICE-5G from the University of Toronto. Our results indicate that the lithospheric thickness varies, depending on the ice model used, between 60 and 160 km. The lowest values are found in the Oslo Graben area and the western German Baltic Sea coast. In between, thickness increases by at least 30 km tracing the Ringkøbing-Fyn High. In Poland and Lithuania, lithospheric thickness reaches up to 160 km. However, the latter values are not well constrained as the confidence regions are large. Upper-mantle viscosity is found to bracket [2-7] × 1020 Pa s when using ICE-5G. Employing RSES much higher values of 2 × 1021 Pa s are obtained for the southern Baltic Sea. Further investigations should evaluate whether this ice-model version and/or the RSL data need revision. We confirm that the lower-mantle viscosity in Fennoscandia can only be poorly resolved. The lithospheric structure inferred from RSES partly supports structural features of regional and global lithosphere models based on thermal or seismological data. While there is agreement in eastern Europe and southwest Sweden, the structure in an area from south of Norway to northern Germany shows large discrepancies for two of the tested lithosphere models. The lithospheric thickness as determined with ICE-5G does not agree with the lithosphere models. Hence, more investigations have to be undertaken to sufficiently determine structures such as the Ringkøbing- Fyn High as seen with seismics with the help of glacial isostatic adjustment modelling. © Author(s) 2014.

Poutanen M.,Finnish Geodetic Institute | Steffen H.,Lantmateriet
Geophysica | Year: 2015

The land uplift is a well-known process at the coastal areas of the Gulf of Bothnia in Finland and Sweden. Today, about 700 hectares of new land is rising from the sea every year. This is changing the landscape rapidly, especially at the shallow coastlines and archipelago of Kvarken in Finland where during the last century the uplift rate relative to the sea has been almost 9 mm/year. At the opposite side in Sweden, the High Coast has much steeper landscape and changes there are less prominent during one generation. Due to its unique nature, the area has received the UNESCO World Heritage status. The area is near the uplift maximum of the Fennoscandian postglacial rebound. Since the end of the deglaciation, a total of at least 286 meters of uplift has occurred up to now, which corresponds to the highest point of the ancient shoreline at Skuleberget at the High Coast. The area is expected to almost linearly rise from the sea in the next few thousand years until the remaining about 100 m of depression due to the former ice load are isostatically balanced. With the help of geophysical and climate models future scenarios of land emergence are predicted based on current observations. The apparent uplift rate relative to the sea depends on the future global sea level rise. We also discuss future scenarios of the landscape in this UNESCO World Heritage area. © 2015, Finish Environment Institute. All rights reserved.

Agren J.,Lantmateriet | Svensson R.,Lantmateriet
Mapping and Image Science | Year: 2011

The computation of the latest precise levellings in Finland, Norway and Sweden was made as a Nordic co-operation within the Working Group for Height Determination of the Nordic Geodetic Commission (NKG). This work includes the compilation of the Baltic Levelling Ring (BLR), which consists of precise levellings from all the Nordic and Baltic countries as well as Poland, Germany and the Netherlands. The main purpose of this paper is to describe the choice of system definition and computation of the postglacial land uplift model for the final adjustment of the BLR. The result of this adjustment constitutes the Swedish height system RH 2000. Initially, it was decided that the new system should be a realisation of the European Vertical Reference System (EVRS) using the Normaal Amsterdams Peil (NAP) as zero level. The final land uplift model is a combination of the geophysical model of Lambeck, Smither and Ekman and the mathematical (empirical) model of Vestøl. It has later been adopted as a Nordic model with the name NKG 2005LU. We describe the path leading to this model and analyse the consequences of the chosen definition and uplift model by comparing the resulting heights to Mean Sea Level (MSL) in the Nordic and Baltic Seas and to the old Swedish height system RH 70. We finally discuss the role of the land uplift model in the modern Swedish geodetic infrastructure.

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