Strain accumulation along an oblique plate boundary: the Reykjanes Peninsula, southwest Iceland

Keiding, Marie; Árnadóttir, Þóra; Sturkell, Erik; Geirsson, H.; Lund, Björn

doi:10.1111/j.1365-246x.2007.03655.x

Cited by 44 publications

(46 citation statements)

References 36 publications

(65 reference statements)

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“…The 10 km long Vogar fissure swarm lies in the northern portion of the 35 km long and 5–8 km wide Reykjanes fissure swarm, in southern Iceland (Figures a and b) [ Gudmundsson , ; Villemin and Bergerat , ; Clifton and Kattenhorn , ]. The amount of pure extension in this highly oblique portion of rift is ~6 mm/yr [ Keiding et al ., ]. The Vogar fissure swarm consists of a 3–4.5 km wide asymmetric deformation zone delimited on the western edge by an east facing normal fault (Hrafnagjá) and on the eastern edge by a series of open fissures (Grindavikurgjá) [ Villemin and Bergerat , ].…”

Section: Resultsmentioning

confidence: 99%

Fault and graben growth along active magmatic divergent plate boundaries in Iceland and Ethiopia

et al. 2015

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Recent studies highlight the importance of annual‐scale dike‐induced rifting episodes in developing normal faults and graben along the active axis of magmatic divergent plate boundaries (MDPB). However, the longer‐term (102–105 years) role of diking on the cumulative surface deformation and evolution of MDPB is not yet well understood. To better understand the longer‐term normal faults and graben along the axis of MDPB, we analyze fissure swarms in Iceland and Ethiopia. We first focus on the simplest case of immature fissure swarms, with single dike‐fed eruptive fissures; these consist of a <1 km wide graben bordered by normal faults with displacement up to a few meters, consistent with theoretical models and geodetic data. A similar structural pattern is found, with asymmetric and multiple graben, within wider mature fissure swarms, formed by several dike‐fed eruptive fissures. We then consider the lateral termination of normal faults along these grabens to detect their upward or downward propagation. Most faults terminate as open fractures on flat surface, suggesting downward fault propagation; this is consistent with recent experiments showing dike‐induced normal faults propagating downward from the surface. However, some normal faults also terminate as open fractures on monoclines, which resemble fault propagation folds; this suggests upward propagation of reactivated buried faults, promoted by diking. These results suggest that fault growth and graben development, as well as the longer‐term evolution of the axis of MDPB, may be explained only through dike emplacement and that any amagmatic faulting is not necessary.

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Section: Resultsmentioning

confidence: 99%

Fault and graben growth along active magmatic divergent plate boundaries in Iceland and Ethiopia

et al. 2015

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“…Hreinsdóttir et al (2001) suggested a temporal partitioning of strain in which left-lateral shear strain is being accommodated during the current "amagmatic" period, and propose that extensional strain is accommodated during magmatic episodes. The most recent GPS data (Keiding et al 2008) call into question the component of subsidence toward the plate boundary axis, and reveal both a major component of shear and a lesser component of extension across the plate boundary. While all of these recent measurements indicate that the RP is currently accommodating more shear than extension, the majority of surface structures are NE striking extensional features.…”

Section: Reykjanes Peninsulamentioning

confidence: 98%

Controls on the geometry of a Holocene crater row: a field study from southwest Iceland

Jenness¹,

Clifton

2009

Bull Volcanol

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The Reykjanes Peninsula rift zone in southwest Iceland is a highly oblique segment of the Mid-Atlantic ridge system which accommodates NW-SE extension during rifting episodes that consist of eruptions and normal faulting, and E-W left-lateral shear strain along strike-slip faults during longer amagmatic periods. Dominant tectonic features on the peninsula are a series of generally NEstriking, sub-parallel eruptive fissures and normal faults, and a cross-cutting zone of N-S striking, right-lateral strike-slip faults. The last series of rifting episodes ended in 1227, and a proposed 1,000 year cyclicity predicts the start of a new series of eruptions within the next 200 years. In order to more accurately characterize the nature of eruptions on the Reykjanes Peninsula, we present a new, spatially accurate map of the ∼2,350 year old Sundhnúkur crater row in the western part of the peninsula, which was examined in detail in order to determine the structural controls on crater row geometry and to understand the interactions that take place between eruptive fissures and pre-existing geological structures. Volcanism is sometimes influenced by small perturbations in the surroundings such as gravitational loading, topography, changes in crustal properties or the presence of fault zones, but there are few field examples showing how fissures are influenced by these pre-existing structures. We identify 27 fissure segments, ranging in strike from 006°to 053°, with varying spacing and overlap between them. Significant local variability in strike and stepping sense of segments occurs in proximity to topographic highs as well as within zones of faulting that pre-date the crater row. Strike also varies at the northern end of the crater row as it approaches a region of older crust at the rift margin. Our data support numerical and laboratory modeling results which show that local topography, pre-existing fractures and crustal properties influence the path taken by magma on its way through the shallow crust.

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“…Annual campaign style GPS measurements have been conducted in the SISZ since June 2000 (Árnadóttir et al, ; Decriem et al, ; Juncu et al, ; Keiding et al, ). Figure shows the network of campaign benchmarks and continuously operating GPS stations in South Iceland.…”

Section: Gps Data and Analysismentioning

confidence: 99%

A Preseismic Strain Anomaly Detected Before M6 Earthquakes in the South Iceland Seismic Zone From GPS Station Velocities

et al. 2018

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The South Iceland Seismic Zone (SISZ) accommodates E‐W translation due to oblique spreading between the North American and the Eurasian plates in South Iceland with ruptures on N‐S faults. Strain is released in earthquake sequences that last days to years, at average intervals of 80–100 years. Two M6.5 earthquakes struck in the SISZ in June 2000, and two M6 earthquakes in May 2008. These events released only half of the strain accumulated since the last earthquake sequence in 1896–1912. GPS station velocities are estimated from annual campaigns and continuous measurements in the SISZ during 2001–2015. The GPS station velocities are used to calculate strain rates from a new method using the vertical derivatives of horizontal stress. Our new strain rates are obtained by integrating vertical derivatives of horizontal stress rates, rather than differentiating interpolated GPS velocities, allowing finer resolution of strain. Estimating the strain rates for eight time intervals, we find high strain rates in the SISZ (0.5–1 microstrain per year) with significant temporal and spatial variation. The strain rates in the SISZ reveal contraction in the Hengill area and dilatation over a large area in eastern SISZ, indicating inflation of the magma system beneath Hekla volcano. A prominent strain anomaly is evident in the epicentral area prior to the May 2008 earthquakes. We suggest that this signal is primarily caused by plate motion and an increase in the rate of contraction in the Hengill area, located ∼10 km west of the epicentral area.

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Strain accumulation along an oblique plate boundary: the Reykjanes Peninsula, southwest Iceland

Cited by 44 publications

References 36 publications

Fault and graben growth along active magmatic divergent plate boundaries in Iceland and Ethiopia

Fault and graben growth along active magmatic divergent plate boundaries in Iceland and Ethiopia

Controls on the geometry of a Holocene crater row: a field study from southwest Iceland

A Preseismic Strain Anomaly Detected Before M6 Earthquakes in the South Iceland Seismic Zone From GPS Station Velocities

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