| 1. |
- Geirsson, Halldor, et al.
(författare)
-
Volcano deformation at active plate boundaries : Deep magma accumulation at Hekla volcano and plate boundary deformation in south Iceland
- 2012
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117:B11409
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 2. |
- Árnadóttir, Thóra, et al.
(författare)
-
Glacial rebound and plate spreading : results from the first countrywide GPS observations in Iceland
- 2009
-
Ingår i: Geophysical Journal International. - 0956-540X .- 1365-246X. ; 177:2, s. 691-716
-
Forskningsöversikt (refereegranskat)abstract
- Iceland is one of the few places on Earth where a divergent plate boundary can be observed on land. Direct observations of crustal deformation for the whole country are available for the first time from nationwide Global Positioning System (GPS) campaigns in 1993 and 2004. The plate spreading across the island is imaged by the horizontal velocity field and high uplift rates (>= 10 mm yr(-1)) are observed over a large part of central and southeastern Iceland. Several earthquakes, volcanic intrusions and eruptions occurred during the time spanned by the measurements, causing local disturbances of the deformation field. After correcting for the largest earthquakes during the observation period, we calculate the strain rate field and find that the main feature of the field is the extension across the rift zones, subparallel to the direction of plate motion. Kinematic models of the horizontal plate spreading signal indicate a slightly elevated rate of spreading in the Northern Volcanic Zone (NVZ) (23 +/- 2 mm yr(-1)), while the rates at the other plate boundary segments agree fairly well with the predicted rate of plate spreading (similar to 20 mm yr(-1)) across Iceland. The horizontal ISNET velocities across north Iceland therefore indicate that the excessive spreading rate (>30 mm yr(-1)) observed by GPS in 1987-1992 following the 1975-1984 Krafla rifting episode was significantly slower during 1993-2004. We model the vertical velocities using glacial isostatic adjustment (GIA) due to the recent thinning of the largest glaciers in Iceland. A layered earth model with a 10-km thick elastic layer, underlain by a 30-km thick viscoelastic layer with viscosity 1 x 10(20) Pa s, over a half-space with viscosity similar to 1 x 10(19) Pa s can explain the broad area of uplift in central and southeastern Iceland. A wide area of significant residual uplift ( up to 8 mm yr(-1)) is evident in north Iceland after we subtract the rebound signal from the observed rates, whereas the Reykjanes Peninsula and the Western Volcanic Zone (WVZ) appear to be subsiding at a rate of 4-8 mm yr(-1). We observe a coherent pattern of small but significant residual horizontal motion (up to 3 mm yr(-1)) away from Vatnajokull and the smaller glaciers that is most likely caused by glacial rebound. Our study demonstrates that the velocity field over a large part of Iceland is affected by deglaciation and that this effect needs to be considered when interpreting deformation data to monitor subglacial volcanoes in Iceland.
|
|
| 3. |
- Hensch, Martin, et al.
(författare)
-
Temporal stress changes associated with the 2008 May 29 Mw 6 earthquake doublet in the western South Iceland Seismic Zone
- 2016
-
Ingår i: Geophysical Journal International. - : Oxford University Press (OUP). - 0956-540X .- 1365-246X. ; 204:1, s. 544-554
-
Tidskriftsartikel (refereegranskat)abstract
- On 2008 May 29, two magnitude Mw ~ 6 earthquakes occurred on two adjacent N-S faults in the western South Iceland Seismic Zone. The first main shock was followed approximately 3 s later by the rupture on a parallel fault, about 5 km to the west. An intense aftershock sequence was mostly confined to the western fault and an E-W aligned zone, extending west of the main shock region into the Reykjanes oblique rift. In this study, a total of 325 well-constrained focal mechanisms were obtained using data from the permanent Icelandic SIL seismic network and a temporary network promptly installed in the source region following the main shocks, which allowed a high-resolution stress inversion in short time intervals during the aftershock period. More than 800 additional focal mechanisms for the time period 2001-2009, obtained from the permanent SIL network, were analysed to study stress changes associated with the main shocks. Results reveal a coseismic counter-clockwise rotation of the maximum horizontal stress of 11 +/- 10 degrees ( 95 per cent confidence level) in the main rupture region. From previous fault models obtained by inversion of geodetic data, we estimate a stress drop of about half of the background shear stress on the western fault. With a stress drop of 8-10 MPa, the pre-event shear stress is estimated to 16-20 MPa. The apparent weakness of the western fault may be caused by fault properties, pore fluid pressure and the vicinity of the fault to the western rift zone, but may also be due to the dynamic stress increase on the western fault by the rupture on the eastern fault. Further, a coseismic change of the stress regime-from normal faulting to strike-slip faulting-was observed at the northern end of the western fault. This change could be caused by stress heterogeneities, but may also be due to a southward shift in the location of the aftershocks as compared to prior events.
|
|
| 4. |
- Juncu, Daniel, et al.
(författare)
-
Injection-induced surface deformation and seismicity at the Hellisheidi geothermal field, Iceland
- 2020
-
Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 391
-
Tidskriftsartikel (refereegranskat)abstract
- Induced seismicity is often associated with fluid injection but only rarely linked to surface deformation. At the Hellisheidi geothermal power plant in south-west Iceland we observe up to 2 cm of surface displacements during 2011–2012, indicating expansion of the crust. The displacements occurred at the same time as a strong increase in seismicity was detected and coincide with the initial phase of geothermal wastewater reinjection at Hellisheidi. Reinjection started on September 1, 2011 with a flow rate of around 500 kg/s. Micro-seismicity increased immediately in the area north of the injection sites, with the largest seismic events in the sequence being two M4 earthquakes on October 15, 2011. Semi-continuous GPS sites installed on October 15 and 17, and on November 2, 2011 reveal a transient signal which indicates that most of the deformation occurred in the first months after the start of the injection. The surface deformation is evident in ascending TerraSAR-X data covering June 2011 to May 2012 as well. We use an inverse modeling approach and simulate both the InSAR and GPS data to find the most plausible cause of the deformation signal, investigating how surface deformation, seismicity and fluid injection may be connected to each other. We argue that fluid injection caused an increase in pore pressure which resulted in increased seismicity and fault slip. Both pore pressure increase and fault slip contribute to the surface deformation.
|
|
| 5. |
|
|
| 6. |
- Oddsson, Asmundur, et al.
(författare)
-
Deficit of homozygosity among 1.52 million individuals and genetic causes of recessive lethality
- 2023
-
Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
-
Tidskriftsartikel (refereegranskat)abstract
- Genotypes causing pregnancy loss and perinatal mortality are depleted among living individuals and are therefore difficult to find. To explore genetic causes of recessive lethality, we searched for sequence variants with deficit of homozygosity among 1.52 million individuals from six European populations. In this study, we identified 25 genes harboring protein-altering sequence variants with a strong deficit of homozygosity (10% or less of predicted homozygotes). Sequence variants in 12 of the genes cause Mendelian disease under a recessive mode of inheritance, two under a dominant mode, but variants in the remaining 11 have not been reported to cause disease. Sequence variants with a strong deficit of homozygosity are over-represented among genes essential for growth of human cell lines and genes orthologous to mouse genes known to affect viability. The function of these genes gives insight into the genetics of intrauterine lethality. We also identified 1077 genes with homozygous predicted loss-of-function genotypes not previously described, bringing the total set of genes completely knocked out in humans to 4785.
|
|
| 7. |
- Olafsdottir, Steinunn A., et al.
(författare)
-
Developing ActivABLES for community-dwelling stroke survivors using the Medical Research Council framework for complex interventions
- 2020
-
Ingår i: BMC Health Services Research. - : Springer Science and Business Media LLC. - 1472-6963. ; 20
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Novel technical solutions are called for to promote home-based exercise among community-dwelling stroke survivors supported by their caregivers. Lack of resources and knowledge about how to accomplish it, has been demonstrated. The objective of this study is to describe in detail the development of ActivABLES, a technical intervention to promote home-based exercise and physical activity engagement of community-dwelling stroke survivors with support from their caregivers. Methods: The technical development process of ActivABLES was guided by the Medical Research Council (MRC) framework for development and evaluation of complex interventions as well as by principles of human-centred design and co-design. The main steps included: (1) Synthesis of evidence supporting the inclusion of balance exercises, mobility and walking exercises and exercises for the upper arm; (2) Implementation of initial user studies with qualitative data collection from individual interviews with stroke survivors, and focus group interviews with caregivers and health professionals; (3) Preliminary testing of eight prototypes with seven stroke survivors and their caregivers. Results: After the preliminary testing of eight prototypes, four prototypes were not further developed whereas four prototypes were modified further. In addition, two new prototypes were developed, leaving six prototypes for further modification: 1) ActivFOAM for balance exercises, 2) WalkingSTARR to facilitate walking, 3) ActivBALL for hand exercises, 4) ActivSTICKS for upper arm exercises, and 5) ActivLAMP and 6) ActivTREE which both give visual feedback on progress of daily exercise and physical activities. ActivFOAM, ActivBALL and ActivSTICKS are all connected to a tablet where exercise instructions are given. All the exercise prototypes can be connected to ActivLAMP and ActivTREE to give feedback on how much exercise the user has done. Settings can be individualised and recommended daily time and/or repetition can easily be changed as the user progresses to higher activity levels. Conclusions: The development process of ActivABLES was guided by the principles of human-centred design, with iterative testing of future users, and by the MRC framework of complex intervention, with a repeated process of development and testing. This process resulted in six prototypes which are available for feasibility testing among a small group of community-dwelling stroke survivors.
|
|
| 8. |
- Olafsdottir, Steinunn A., et al.
(författare)
-
Feasibility of ActivABLES to promote home-based exercise and physical activity of community-dwelling stroke survivors with support from caregivers : A mixed methods study
- 2020
-
Ingår i: BMC Health Services Research. - : Springer Science and Business Media LLC. - 1472-6963. ; 20:1
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Technical applications can promote home-based exercise and physical activity of community-dwelling stroke survivors. Caregivers are often able and willing to assist with home-based exercise and physical activity but lack the knowledge and resources to do so. ActivABLES was established to promote home-based exercise and physical activity among community-dwelling stroke survivors, with support from their caregivers. The aim of our study is to investigate the feasibility of ActivABLES in terms of acceptability, demand, implementation and practicality. METHODS: A convergent design of mixed methods research in which quantitative results were combined with personal experiences of a four-week use of ActivABLES by community-dwelling stroke survivors with support from their caregivers. Data collection before, during and after the four-week period included the Berg Balance Scale (BBS), Activities-Specific Balance Confidence Scale (ABC), Timed-Up-and-Go (TUG) and Five Times Sit to Stand Test (5xSST) and data from motion detectors. Semi-structured interviews were conducted with stroke survivors and caregivers after the four-week period. Descriptive statistics were used for quantitative data. Qualitative data was analysed with direct content analysis. Themes were identified related to the domains of feasibility: acceptability, demand, implementation and practicality. Data was integrated by examining any (dis)congruence in the quantitative and qualitative findings. RESULTS: Ten stroke survivors aged 55-79 years participated with their informal caregivers. Functional improvements were shown in BBS (+ 2.5), ABC (+ 0.9), TUG (- 4.2) and 5xSST (- 2.7). More physical activity was detected with motion detectors (stand up/sit down + 2, number of steps + 227, standing + 0.3 h, hours sitting/lying - 0.3 h). The qualitative interviews identified themes for each feasibility domain: (i) acceptability: appreciation, functional improvements, self-initiated activities and expressed potential for future stroke survivors; (2) demand: reported use, interest in further use and need for follow-up; (3) implementation: importance of feedback, variety of exercises and progression of exercises and (4) practicality: need for support and technical problems. The quantitative and qualitative findings converged well with each other and supported the feasibility of ActivABLES. CONCLUSIONS: ActivABLES is feasible and can be a good asset for stroke survivors with slight or moderate disability to use in their homes. Further studies are needed with larger samples.
|
|
| 9. |
- Pagli, Carolina, et al.
(författare)
-
Glacio-isostatic deformation around the Vatnajökull ice cap, Iceland, induced by recent climate warming : GPS observations and finite element modeling
- 2007
-
Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 112:B8, s. B08405-
-
Tidskriftsartikel (refereegranskat)abstract
- [1] Glaciers in Iceland began retreating around 1890, and since then the Vatnajokull ice cap has lost over 400 km 3 of ice. The associated unloading of the crust induces a glacio-isostatic response. From 1996 to 2004 a GPS network was measured around the southern edge of Vatnajokull. These measurements, together with more extended time series at several other GPS sites, indicate vertical velocities around the ice cap ranging from 9 to 25 mm/yr, and horizontal velocities in the range 3 to 4 mm/yr. The vertical velocities have been modeled using the finite element method (FEM) in order to constrain the viscosity structure beneath Vatnajokull. We use an axisymmetric Earth model with an elastic plate over a uniform viscoelastic half-space. The observations are consistent with predictions based on an Earth model made up of an elastic plate with a thickness of 10-20 km and an underlying viscosity in the range 4-10 x 10(18) Pa s. Knowledge of the Earth structure allows us to predict uplift around Vatnajokull in the next decades. According to our estimates of the rheological parameters, and assuming that ice thinning will continue at a similar rate during this century (about 4 km 3/year), a minimum uplift of 2.5 meters between 2000 to 2100 is expected near the current ice cap edge. If the thinning rates were to double in response to global warming (about 8 km 3/year), then the minimum uplift between 2000 to 2100 near the current ice cap edge is expected to be 3.7 meters.
|
|
| 10. |
- Schmidt, Peter, et al.
(författare)
-
Effects of present day deglaciation on melt production rates beneath Iceland
- 2013
-
Ingår i: Journal of Geophysical Research-Solid Earth. - : American Geophysical Union (AGU). - 2169-9313. ; 118:7, s. 3366-3379
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 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.
|
|
