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Schmidt, Peter
Publications (10 of 11) Show all publications
Schmidt, P., Lund, B., Näslund, J.-O. & Fastook, J. (2014). Comparing a thermo-mechanical Weichselian Ice Sheet reconstruction to reconstructions based on the sea level equation: aspects of ice configurations and glacial isostatic adjustment. Solid Earth, 5(1), 371-388
Open this publication in new window or tab >>Comparing a thermo-mechanical Weichselian Ice Sheet reconstruction to reconstructions based on the sea level equation: aspects of ice configurations and glacial isostatic adjustment
2014 (English)In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529, Vol. 5, no 1, p. 371-388Article in journal (Refereed) Published
Abstract [en]

In this study we compare a recent reconstruction of the Weichselian Ice Sheet as simulated by the University of Maine ice sheet model (UMISM) to two reconstructions commonly used in glacial isostatic adjustment (GIA) modelling: ICE-5G and ANU (Australian National University, also known as RSES). The UMISM reconstruction is carried out on a regional scale based on thermo-mechanical modelling, whereas ANU and ICE-5G are global models based on the sea level equation. The three models of the Weichselian Ice Sheet are compared directly in terms of ice volume, extent and thickness, as well as in terms of predicted glacial isostatic adjustment in Fennoscandia. The three reconstructions display significant differences. Whereas UMISM and ANU includes phases of pronounced advance and retreat prior to the last glacial maximum (LGM), the thickness and areal extent of the ICE-5G ice sheet is more or less constant up until the LGM. During the post-LGM deglaciation phase ANU and ICE-5G melt relatively uniformly over the entire ice sheet in contrast to UMISM, which melts preferentially from the edges, thus reflecting the fundamental difference in the reconstruction scheme. We find that all three reconstructions fit the present-day uplift rates over Fennoscandia equally well, albeit with different optimal earth model parameters. Given identical earth models, ICE-5G predicts the fastest present-day uplift rates, and ANU the slowest. Moreover, only for ANU can a unique best-fit model be determined. For UMISM and ICE-5G there is a range of earth models that can reproduce the present-day uplift rates equally well. This is understood from the higher present-day uplift rates predicted by ICE-5G and UMISM, which result in bifurcations in the best-fit upper-and lower-mantle viscosities. We study the areal distributions of present-day residual surface velocities in Fennoscandia and show that all three reconstructions generally over-predict velocities in southwestern Fennoscandia and that there are large differences in the fit to the observational data in Finland and northernmost Sweden and Norway. These difference may provide input to further enhancements of the ice sheet reconstructions.

National Category
Geophysics
Research subject
Geophysics with specialization in Seismology
Identifiers
urn:nbn:se:uu:diva-226027 (URN)10.5194/se-5-371-2014 (DOI)000337218200025 ()
Available from: 2014-06-10 Created: 2014-06-10 Last updated: 2017-12-05Bibliographically approved
Dorostkar, A., Lukarski, D., Lund, B., Neytcheva, M., Notay, Y. & Schmidt, P. (2014). CPU and GPU performance of large scale numerical simulations in Geophysics. In: Euro-Par 2014: Parallel Processing Workshops, Part I. Paper presented at 1st Workshop on Applications of Parallel Computation in Industry and Engineering (pp. 12-23). Springer
Open this publication in new window or tab >>CPU and GPU performance of large scale numerical simulations in Geophysics
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2014 (English)In: Euro-Par 2014: Parallel Processing Workshops, Part I, Springer, 2014, p. 12-23Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Springer, 2014
Series
Lecture Notes in Computer Science ; 8805
National Category
Computer Sciences Geophysics
Identifiers
urn:nbn:se:uu:diva-238254 (URN)10.1007/978-3-319-14325-5_2 (DOI)000354783500002 ()978-3-319-14324-8 (ISBN)
Conference
1st Workshop on Applications of Parallel Computation in Industry and Engineering
Projects
UPMARCeSSENCE
Available from: 2014-12-10 Created: 2014-12-10 Last updated: 2018-01-11Bibliographically approved
Dorostkar, A., Lukarski, D., Lund, B., Neytcheva, M., Notay, Y. & Schmidt, P. (2014). Parallel performance study of block-preconditioned iterative methods on multicore computer systems.
Open this publication in new window or tab >>Parallel performance study of block-preconditioned iterative methods on multicore computer systems
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2014 (English)Report (Other academic)
Series
Technical report / Department of Information Technology, Uppsala University, ISSN 1404-3203 ; 2014-007
National Category
Computer Sciences Computational Mathematics
Identifiers
urn:nbn:se:uu:diva-223795 (URN)
Projects
eSSENCEUPMARC
Available from: 2014-03-19 Created: 2014-04-25 Last updated: 2018-01-11Bibliographically approved
Schmidt, P., Lund, B., Hieronymus, C., Maclennan, J., Árnadóttir, T. & Pagli, C. (2013). Effects of present day deglaciation on melt production rates beneath Iceland. Journal of Geophysical Research-Solid Earth, 118(7), 3366-3379
Open this publication in new window or tab >>Effects of present day deglaciation on melt production rates beneath Iceland
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2013 (English)In: Journal of Geophysical Research-Solid Earth, ISSN 2169-9313, Vol. 118, no 7, p. 3366-3379Article in journal (Other academic) Published
Abstract [en]

Ongoing deglaciation in Iceland not only causes uplift at the surface but also increases magma production at depth due to decompression of the mantle. Here we study glacially induced decompression melting using 3-D models of glacial isostatic adjustment in Iceland since 1890. We find that the mean glacially induced pressure rate of change in the mantle increases melt production rates by 100–135%, or an additional 0.21–0.23 km3 of magma per year beneath Iceland. Approximately 50% of this melt is produced underneath central Iceland. The greatest volumetric increase is found directly beneath Iceland's largest ice cap, Vatnajökull, colocated with the most productive volcanoes. Our models of the effect of deglaciation on mantle melting predict a significantly larger volumetric response than previous models which only considered the effect of deglaciation of Vatnajökull, and only mantle melting directly below Vatnajökull. Although the ongoing deglaciation significantly increases the melt production rate, the increase in melt supply rate at the base of the lithosphere is delayed and depends on the melt ascent velocity through the mantle. Assuming that 25% of the melt reaches the surface, the upper limit on our deglaciation-induced melt estimates for central Iceland would be equivalent to an eruption the size of the 2010 Eyjafjallajökull summit eruption every seventh year.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2013
Keywords
decompression melting, GIA, Iceland, mantle melting, volcanism, deglaciation
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-169788 (URN)10.1002/jgrb.50273 (DOI)000324952300008 ()
Available from: 2012-03-06 Created: 2012-03-06 Last updated: 2013-11-04Bibliographically approved
Auriac, A., Spaans, K. H., Sigmundsson, F., Hooper, A., Schmidt, P. & Lund, B. (2013). Iceland rising: Solid Earth response to ice retreat inferred from satellite radar interferometry and visocelastic modeling. Journal of Geophysical Research, 118(4), 1331-1344
Open this publication in new window or tab >>Iceland rising: Solid Earth response to ice retreat inferred from satellite radar interferometry and visocelastic modeling
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2013 (English)In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 4, p. 1331-1344Article in journal (Refereed) Published
Abstract [en]

A broad uplift occurs in Iceland in response to the retreat of ice caps, which began circa 1890. Until now, this deformation signal has been measured primarily using GPS at points some distance away from the ice caps. Here, for the first time we use satellite radar interferometry (interferometric synthetic aperture radar) to constrain uplift of the ground all the way up to the edge of the largest ice cap, Vatnajokull. This allows for improved constraints on the Earth rheology, both the thickness of the uppermost Earth layer that responds only in an elastic manner and the viscosity below it. The interferometric synthetic aperture radar velocities indicate a maximum displacement rate of 24 +/- 4 and 31 +/- 4 mm/yr at the edge of Vatnajokull, during 1995-2002 and 2004-2009, respectively. The fastest rates occur at outlet glaciers of low elevation where ice retreat is high. We compare the observations with glacial isostatic adjustment models that include the deglaciation history of the Icelandic ice caps since 1890 and two Earth layers. Using a Bayesian approach, we derived probability density functions for the average Earth model parameters for three satellite tracks. Based on our assumptions, the three best fit models give elastic thicknesses in the range of 15-40 km, and viscosities ranging from 4-10x1018 Pa s.

Keywords
InSAR, Finite element modeling, Rheology, GIA
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-203685 (URN)10.1002/jgrb.50082 (DOI)000319926600001 ()
Available from: 2013-07-18 Created: 2013-07-17 Last updated: 2017-12-06Bibliographically approved
Sigmundsson, F., Albino, F., Schmidt, P., Lund, B., Pinel, V., Hooper, A. & Pagli, C. (2013). Multiple effects of ice load changes and associated stress change on magmatic systems. In: W.J. McGuire, M.A. Maslin (Ed.), Climate Forcing of Geological and Geomorphological Hazards: . John Wiley & Sons
Open this publication in new window or tab >>Multiple effects of ice load changes and associated stress change on magmatic systems
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2013 (English)In: Climate Forcing of Geological and Geomorphological Hazards / [ed] W.J. McGuire, M.A. Maslin, John Wiley & Sons, 2013Chapter in book (Refereed)
Place, publisher, year, edition, pages
John Wiley & Sons, 2013
Keywords
ce load; magma stress; glacial unloading; crust/mantle; magma geometry
National Category
Geophysics
Research subject
Geophysics with specialization in Seismology
Identifiers
urn:nbn:se:uu:diva-209343 (URN)10.1002/9781118482698.ch5 (DOI)
Available from: 2013-10-17 Created: 2013-10-17 Last updated: 2014-01-21Bibliographically approved
Schmidt, P., Lund, B., Árnadóttir, T. & Schmeling, H. (2012). Glacial isostatic adjustment constrains dehydration stiffening beneath Iceland. Earth and Planetary Science Letters, 359-360, 152-161
Open this publication in new window or tab >>Glacial isostatic adjustment constrains dehydration stiffening beneath Iceland
2012 (English)In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 359-360, p. 152-161Article in journal (Refereed) Published
Abstract [en]

During melting in the upper mantle the preferred partitioning of water into the melt will effectively dehydrate the solid residue. Linear extrapolation of laboratory experiments suggests that dehydration can produce a sharp viscosity contrast (increase) of a factor 500 across the dry solidus. In this study we show that the suggested magnitude of dehydration stiffening in a plume–ridge setting is incompatible with the present glacial isostatic adjustment (GIA) in Iceland. Using GPS observations of current GIA in Iceland, we find that the data are best fit by a viscosity contrast over the dry solidus in the range 0.5–3. A viscosity contrast higher than 10 requires a mantle viscosity below the dry solidus lower than , depending on the thickness of the dehydrated layer. A viscosity contrast of 100 or more demands a mantle viscosity of or less. However, we show here that a non-linear extrapolation of the laboratory data predicts a viscosity contrast as low as a factor 3–29, assuming conditions of constant strain rate to constant viscous dissipation rate. This is compatible with our GIA results and suggests that the plume–ridge interaction beneath Iceland is governed by a non-linear rheology and controlled by a combination of kinematic and dynamic boundary conditions rather than buoyant forces alone.

Keywords
glacial isostatic adjustment, Iceland, dehydration stiffening, rheology, viscosity
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-169787 (URN)10.1016/j.epsl.2012.10.015 (DOI)000312924200016 ()
Available from: 2012-03-06 Created: 2012-03-06 Last updated: 2017-12-07Bibliographically approved
Schmidt, P. (2012). Glacial Isostatic Adjustment: Inferences on properties and processes in the upper mantle from 3D dynamical modeling. (Doctoral dissertation). Uppsala: Acta Universitatis Upsaliensis
Open this publication in new window or tab >>Glacial Isostatic Adjustment: Inferences on properties and processes in the upper mantle from 3D dynamical modeling
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Observations of glacial isostatic adjustment (GIA) offers a powerful window into the properties of the Earth's interior. Combined with dynamical modeling of the GIA process we can use the observations to infer properties such as the elastic structure of the lithosphere, the rheology of the mantle and changes in the stress conditions in the Earth. This information aids our understanding of the long term evolution of the Earth, e.g. mantle convection, but also illuminates short term processes such as magma generation, earthquakes and shoreline migration. As present day warming trends causes glacier retreat world wide, GIA offers the opportunity to gain local insight into the Earth.

In this thesis I develop an implementation of the pre-stress advection term in finite element modeling. I apply this to current GIA in Iceland, and conclude that local variations in the elastic thickness of the lithosphere can potentially be detected close to the largest ice cap. I study the magnitude of dehydration stiffening in the uppermost Icelandic mantle. The results indicate that the increase in viscosity over the dry solidus is of small magnitude, implying a non-linear rheology in the uppermost mantle beneath Iceland. The present deglaciation in Iceland causes additional melting of the mantle. I find an increased melt production rate of 100-140% at present, although the melt supply rate at the base of the lithosphere is found to be delayed, with estimated present day perturbations ranging from neglible up to 120%.

In the last section of the thesis I focus on the role of ice sheet reconstructions in GIA modeling. I compare three reconstruction of the Weichselian ice sheet and discuss similarities and difference as well as the fit to present day uplift rates in Fennoscandia. The results provide input to improvements in the ice sheet models.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. p. 83
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 906
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-169790 (URN)978-91-554-8294-7 (ISBN)
Public defence
2012-04-20, Hamberg, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2012-03-29 Created: 2012-03-06 Last updated: 2012-04-19Bibliographically approved
Schmidt, P., Lund, B. & Hieronymus, C. (2012). Implementation of the glacial rebound pre-stress advection correction in general-purpose finite element analysis software: Springs versus foundations. Computers & Geosciences, 40, 97-106
Open this publication in new window or tab >>Implementation of the glacial rebound pre-stress advection correction in general-purpose finite element analysis software: Springs versus foundations
2012 (English)In: Computers & Geosciences, ISSN 0098-3004, E-ISSN 1873-7803, Vol. 40, p. 97-106Article in journal (Refereed) Published
Abstract [en]

When general-purpose finite element analysis software is used to model glacial isostatic adjustment (GIA), the first-order effect of prestress advection has to be accounted for by the user. We show here that the common use of elastic foundations at boundaries between materials of different densities will produce incorrect displacements, unless the boundary is perpendicular to the direction of gravity. This is due to the foundations always acting perpendicular to the surface to which they are attached, while the body force they represent always acts in the direction of gravity. If prestress advection is instead accounted for by the use of elastic spring elements in the direction of gravity, the representation will be correct. The use of springs adds a computation of the spring constants to the analysis. The spring constant for a particular node is defined by the product of the density contrast at the boundary, the gravitational acceleration, and the area supported by the node. To be consistent with the finite element formulation, the area is evaluated by integration of the nodal shape functions. We outline an algorithm for the calculation and include a Python script that integrates the shape functions over a bilinear quadrilateral element. For linear rectangular and triangular elements, the area supported by each node is equal to the element area divided the number of defining nodes, thereby simplifying the computation. This is, however, not true in the general nonrectangular case, and we demonstrate this with a simple 1-element model. The spring constant calculation is simple and performed in the preprocessing stage of the analysis. The time spent on the calculation is more than compensated for by a shorter analysis time, compared to that for a model with foundations. We illustrate the effects of using springs versus foundations with a simple two-dimensional GIA model of glacial loading, where the Earth model has an inclined boundary between the overlying elastic layer and the lower viscoelastic layer. Our example shows that the error introduced by the use of foundations is large enough to affect an analysis based on high-accuracy geodetic data.

National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-159553 (URN)10.1016/j.cageo.2011.07.017 (DOI)000301624600009 ()
Available from: 2011-10-04 Created: 2011-10-04 Last updated: 2017-12-08Bibliographically approved
Geirsson, H., LaFemina, P., Arnadottir, T., Sturkell, E., Sigmundsson, F., Travis, M., . . . Bennett, R. (2012). Volcano deformation at active plate boundaries: Deep magma accumulation at Hekla volcano and plate boundary deformation in south Iceland. Journal of Geophysical Research, 117, B11409
Open this publication in new window or tab >>Volcano deformation at active plate boundaries: Deep magma accumulation at Hekla volcano and plate boundary deformation in south Iceland
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2012 (English)In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. B11409-Article in journal (Refereed) Published
Abstract [en]

Most magmatic systems on Earth are located at actively deforming plate boundaries. In these systems, the magmatic and plate boundary deformation signals are intertwined and must be deconvolved to properly estimate magma flux and source characteristics of the magma plumbing system. We investigate the inter-rifting and inter-seismic deformation signals at the Eastern Volcanic Zone (EVZ) - South Iceland Seismic Zone (SISZ) ridge - transform intersection and estimate the location, depth, and volume rate for magmatic sources at Hekla and Torfajokull volcanoes, which are located at the intersection. We solve simultaneously for the source parameters of the tectonic and volcanic deformation signals using a new ten-year velocity field derived from a dense network of episodic and continuous GPS stations in south Iceland. We find the intersection of the axes of the EVZ and the SISZ is located within the Torfajokull caldera, which itself is subsiding. Deformation at Hekla is statistically best described in terms of a horizontal ellipsoidal magma chamber at 24(2)(+4) km depth aligned with the volcanic system and increasing in volume by 0.017(-0.002)(+0.007) km(3) per year. A spherical magma chamber centered at 24(-2)(+5) km depth with a volume rate of 0.019(-0.002)(+0.011) km(3) per year, or a vertical pipe-shaped magma chamber between 10(-1)(+3) km and 21(-4)(+7) km with a volume rate of 0.008(-0.001)(+0.003) km(3) per year are also plausible models explaining the deformation at Hekla. All three models indicate magma accumulation in the lower crust or near the Moho under Hekla.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-189149 (URN)10.1029/2012JB009400 (DOI)000311566100002 ()
Available from: 2013-01-03 Created: 2012-12-25 Last updated: 2017-12-06Bibliographically approved
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