GPS epoch measurements spanning the mid-Atlantic plate boundary in Northern Iceland 1987–1990

Jahn, Cord-Hinrich; Seeber, Günter; Foulger, G. R.; Einarsson, Páll

doi:10.1029/gm082p0109

Cited by 6 publications

(3 citation statements)

References 12 publications

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“…These movements decay with time in an exponential way. Post-rifting movements were measured after the Kraa events (Jahn et al, 1994;Foulger et al, 1992;Heki et al, 1993;Völksen and Seeber, 1998) but appear to be over according to the 1993-2004 ÍSNET results (Árnadóttir et al, this issue).…”

Section: The Northern Volcanic Zonementioning

confidence: 97%

Plate boundaries, rifts and transforms in Iceland

Einarsson

2008

Jök

193

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The Iceland hotspot has a pronounced effect on the appearance and structure of the plate boundary between the North America and Eurasia Plates that crosses the island. The thick crust produced by the excess magmatism of the hotspot leads to a wider and more complicated plate boundary deformation zone than is observed along normal oceanic plate boundaries. Furthermore, the relative movement of the boundary with respect to the roots of the hotspot leads to unstable boundaries and rift jumps, when crustal blocks or microplates are transferred from one major plate to the other. The plate boundary zone can be divided into segments that are physiographically relatively homogeneous and possess distinct tectonic characteristics. The segments are more or less oblique to the relative spreading direction of the two major plates. The divergent component of the movements is taken up by diking and normal faulting and is usually concentrated in the ssure swarms of the volcanic systems. The transcurrent component of the movements is often accommodated by strike-slip faulting on faults that are transverse to the plate boundary segment, so-called bookshelf faults, witnessing to the transient nature of the segments. In highly oblique segments, such as the Reykjanes Peninsula Rift and the Grímsey Oblique Rift, both types of active structures occur superimposed on each other. In the South Iceland Seismic Zone, that is almost parallel to the local spreading direction, the bookshelf faults dominate the structure, producing earthquakes as large as magnitude 7. More mature transform zones, such as the Húsavík-Flatey faults, have developed strike-slip faults that are sub-parallel to the plate movements. The activity on this transform zone, however, appears to be declining because of transfer of movement over to the Grímsey zone. This is supported by the lack of Holocene volcanism along the Eyjafjarðaráll Rift that connects the transform to the Kolbeinsey Ridge plate boundary off shore. A ridge-jump appears to be in progress in South Iceland, where rifting is occurring in two sub-parallel rift zones, the very active Eastern Volcanic Zone and the less active Western Volcanic Zone. The block between them is seismically and volcanically inert and may be dened as a microplate, the Hreppar Microplate. It is rotating in response to the southward propagation of the Eastern Volcanic Zone and corresponding recess of the Western Volcanic Zone. Poles of relative rotation with respect to the North America and Eurasia Plates are suggested near 65.2

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Section: The Northern Volcanic Zonementioning

confidence: 97%

Plate boundaries, rifts and transforms in Iceland

Einarsson

2008

Jök

193

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“…The vertical displacement field obtained from independent processing using the G EONAP software reveals a very similar pattern to that obtained using the Bernese results (Figure 14a) (C.-H. Jahn, personal communication, 1995), which suggests that the deformation is not an artifact of the data processing method. Dike injection in an elastic half-space produces horizontal displacement fields that increase steeply to a peak within a few tens of kilometers from the spreading axis and then fall off more slowly at greater distances (Figure 17a) [Foulget et al, 1994]. Zero vertical motion is predicted along the spreading axis, with substantial uplift on either side, peaking somewhat closer to the spreading axis than the horizontal motions, and decreasing with distance to zero farther away (Figure 17b).…”

Section: Observed Variations Of Vp and Thementioning

confidence: 98%

Postrifting anelastic deformation around the spreading plate boundary, north Iceland: 1. Modeling of the 1987–1992 deformation field using a viscoelastic Earth structure

Hofton¹,

Foulger²

1996

J. Geophys. Res.

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A third Global Positioning System (GPS) survey of a regional network surrounding the Krafla volcanic system, north Iceland, was conducted in 1992 following a major crustal spreading episode which began in this system in 1975. Differencing the 1992 results with those from 1987 and 1990 reveals a regional deformation field with a maximum, rift‐normal expansion rate of 4.5 cm/year near the rift, decreasing to 3 cm/year at large distances. The time‐averaged spreading rate in north Iceland, 1.8 cm/year, cannot account for this deformation. The vertical deformation field reveals regional uplift throughout the network area at its maximum closest to the rift and decreasing with distance. Three different models are applied to study the postdike injection ground deformation: (1) stress redistribution in an elastic layer over a viscoelastic half‐space, (2) stress redistribution in an elastic‐viscous layered medium, and (3) continued opening at depth on the dike plane in an elastic half‐space. Using model 1, the effects of historical episodes in the region are subtracted from the observed displacement fields, and the remaining motion is modeled as relaxation following the recent Krafla rifting episode. The best fit model involves a half‐space viscosity of 1.1 × 1018 Pa s, a relaxation time of 1.7 years, and an elastic layer thickness for northeast Iceland of 10 km. The vertical field indicates that the Krafla dike complex rifted the entire elastic layer. Using model 2, the motion 1987–1990 and 1990–1992 can be simulated adequately given the survey errors, but the 1987–1992 deformation is poorly fitted, suggesting that a more realistic geophysical model is required. Using model 3, a range of dikes will fit the deformation field.

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“…The fieldwork, data processing and interpretation of the results were conducted cooperatively by the University of Durham, UK, and the University of Hannover, Germany, with contributions to the fieldwork by Icelandic institutions for some surveys Heki et al 1993;Jahn et al 1994;Voelksen et al 1995;Hofton 1995;Hofton & Foulger 1996a, b).…”

Section: Regional Gps Surveys In the Eastern Half Of Icelandmentioning

confidence: 99%

Regional vertical motion in Iceland 1987–1992, determined using GPS surveying

Foulger

Hofton

1999

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Vertical motion in Iceland may arise from tectonic sources, e.g. large earthquakes and spreading episodes, isostatic movements owing to the change in mass of icecaps, and secular sinking of the volcanic pile under its own weight. Regional Global Positioning System (GPS) surveys covering the eastern half of Iceland have revealed the vertical motion for the period 1987-1992. Although the errors associated with the vertical component are large, exceptionally good agreement between independent data processing and agreement with isolated terrestrial measurements lends credence to the somewhat surprising results. These are dominated by relative uplift of c. 12 cm in the northern part of the Northern Volcanic Zone and subsidence of up to c. 12cm elsewhere. This motion can be partially explained by recent tectonic and glacio-isostatic events. The most significant of these are the 1975-1984 Krafla spreading episode and isostatic uplift around the currently melting Vatnaj6kull icecap of c. 1 cm/year. However, a substantial amount of the observed motion cannot be explained by any known processes. It is concluded that hitherto unknown, largescale processes associated with the hotspot and plume, possibly continuing at depths of c. 75 km, may be responsible. Behaviour of this kind has been observed associated with the Yellowstone hotspot, which is broadly comparable with the Iceland hotspot. Future remeasurements of the GPS network in Iceland will be valuable for refining these observations.

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GPS epoch measurements spanning the mid-Atlantic plate boundary in Northern Iceland 1987–1990

Cited by 6 publications

References 12 publications

Plate boundaries, rifts and transforms in Iceland

Plate boundaries, rifts and transforms in Iceland

Postrifting anelastic deformation around the spreading plate boundary, north Iceland: 1. Modeling of the 1987–1992 deformation field using a viscoelastic Earth structure

Regional vertical motion in Iceland 1987–1992, determined using GPS surveying

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