The stress pattern of Iceland

Ziegler, Moritz; Rajabi, Mojtaba; Heidbach, Oliver; Hersir, Gylfi Páll; Ágústsson, Kristján; Árnadóttir, Sigurveig; Zang, Arno

doi:10.1016/j.tecto.2016.02.008

Cited by 47 publications

(41 citation statements)

References 117 publications

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“…The observed strikes and motions fit with a maximum principal stress N45˚E to N60˚E [138], in agreement with a S Hmax ranging between N29˚E and N62˚E in South Iceland as deduced from borehole, earthquake and geological data [150].…”

Section: The Structural Patternsupporting

confidence: 85%

Unstable Rifts, a Leaky Transform Zone and a Microplate: Analogues from South Iceland

Khodayar¹,

Björnsson²,

Víkingsson³

et al. 2020

OJG

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A structural analysis was undertaken in the South Iceland Seismic Zone (SISZ) transform zone, and in the Hreppar Microplate (HMP) located between the propagating Eastern Rift Zone (ERZ) and the receding Western Rift Zone (WRZ). The age of the oceanic crust in these areas is 3.4 Ma to present. About 20,000 fracture segments on aerial images reflect the dominance of NNE extensional structures in the WRZ. Around 9,000 basement faults, intrusions, secondary fractures, surface ruptures of earthquakes, and leakages were mapped in the outcrops of the HMP and the SISZ. About 23% of these fractures strike NNE, while 77% are dominantly northerly dextral and ENE sinistral, and secondarily E-W, WNW and NW sinistral strike-and oblique-slip structures, forming a Riedel shear pattern typical of a transform zone. Dyke injections into Riedel shears indicate a leaky transform zone. Fractures reactivated, accumulated slip, and re-opened for fluid flow. The ENE faults dip mostly to the southeast and could be the present boundary of the SISZ to the north. A 10 -30 km wide ENE structural zone hosts a valley to the east, which could be deeper in the west. This ENE zone contains all the earthquakes, dominant ENE rivers, frequent ENE secondary fractures, and is likely the active part of the SISZ. The HMP does not show rotation since 3.4 Ma despite being between two rift segments. Future propagation/recession of the rift segments along their N55˚E sections would cause a migration and a clockwise rotation of the SISZ from ENE to E-W. The boundary faults of the SISZ would then be E-W, with unchanged internal Riedel shears, compensating its sinistral motion. Insights into complexities of diverging plate boundaries are critical for resource management in such tectonic contexts. Figure 1. Geological settings of Iceland and the study area. (a) Active and extinct plate boundaries and microplates in Iceland (modified from [55]); (b) Main geological elements of the study area. Fissure swarms and intraplate volcanism on (a), and the geology and tectonics on (b) are from [122], the petrology of Holocene and Late Pleistocene volcanic systems is from [109], and the earthquakes are from the SIL network of the Icelandic Meteorological Institute (IMO). The rate of spreading is from [121]. M. Khodayar et al.and results in this case study will also benefit exploration and resource management at other diverging oceanic plate boundaries. Geodynamics of Diverging Plate BoundariesAs oblique rifting is absent in the study area, an overview of the key features associated with rift/ridges, transform zones, and microplates is presented below.  Continental rifts and oceanic ridges trend orthogonal to spreading. From initial continental break-up, extension is accommodated by rift boundary normal faults, but intra-rift complexities appear during rift evolution with half-grabens, subsided central grabens/axial valleys, uplifted rift shoulders, rotated fault blocks and detachments [8] [9], as well as ridge segmentation [10] and ridge instability [11] [12]. During thei...

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Section: The Structural Patternsupporting

confidence: 85%

Unstable Rifts, a Leaky Transform Zone and a Microplate: Analogues from South Iceland

Khodayar¹,

Björnsson²,

Víkingsson³

et al. 2020

OJG

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“…However, there are several examples that demonstrate the potential reliability of D quality data records in different regions worldwide. For example, Tingay et al [2010], Reiter et al [2014], and Ziegler et al [2016] clearly demonstrated that the inclusion of D quality data records does not increase the overall stress variability compared to only A-C data interpretation and that the inclusion of D quality data can yield a more representative regional stress orientation in Journal of Geophysical Research: Solid Earth 10.1002/2016JB013178 sedimentary basins. However, it should also be noted that some other studies have suggested that it can be unreliable to include D quality data for the understanding of regional stress pattern, as these data can result in an increase in stress variability due to presence of local structures that show the local pattern of stress [Rajabi et al, 2016a;Rajabi et al, 2016b].…”

Section: Results: S Hmax Orientation Of the Taranaki Basinmentioning

confidence: 99%

Contemporary tectonic stress pattern of the Taranaki Basin, New Zealand

et al. 2016

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The present‐day stress state is a key parameter in numerous geoscientific research fields including geodynamics, seismic hazard assessment, and geomechanics of georeservoirs. The Taranaki Basin of New Zealand is located on the Australian Plate and forms the western boundary of tectonic deformation due to Pacific Plate subduction along the Hikurangi margin. This paper presents the first comprehensive wellbore‐derived basin‐scale in situ stress analysis in New Zealand. We analyze borehole image and oriented caliper data from 129 petroleum wells in the Taranaki Basin to interpret the shape of boreholes and determine the orientation of maximum horizontal stress (SHmax). We combine these data (151 SHmax data records) with 40 stress data records derived from individual earthquake focal mechanism solutions, 6 from stress inversions of focal mechanisms, and 1 data record using the average of several focal mechanism solutions. The resulting data set has 198 data records for the Taranaki Basin and suggests a regional SHmax orientation of N068°E (±22°), which is in agreement with NW‐SE extension suggested by geological data. Furthermore, this ENE‐WSW average SHmax orientation is subparallel to the subduction trench and strike of the subducting slab (N50°E) beneath the central western North Island. Hence, we suggest that the slab geometry and the associated forces due to slab rollback are the key control of crustal stress in the Taranaki Basin. In addition, we find stress perturbations with depth in the vicinity of faults in some of the studied wells, which highlight the impact of local stress sources on the present‐day stress rotation.

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“…2). Maximum horizontal stresses in Iceland are oriented parallel to the rift axes (Ziegler et al, 2016), with a NE-SW trend on 30 the Reykjanes Peninsula Ridge and N-S trend in the North Volcanic Zone. The orientation of the faults, fissures and dikes https://doi.org /10.5194/se-2019-117 Preprint.…”

Section: Geological Background 25mentioning

confidence: 97%

Structure of massively dilatant faults in Iceland: lessons learned from high resolution UAV data

Weismüller

Urai

Kettermann

et al. 2019

Preprint

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Normal faults in basalts develop massive dilatancy up to several tens of meters close to the Earth's surface and show corresponding interactions with groundwater and lava flow. These massively dilatant faults (MDF) are widespread in 15 extensional settings like Iceland or the East African Rift, but their detailed geometry is not well understood, despite their importance for fluid flow in the subsurface, geohazards or geothermal energy. We present a large set of digital elevation models (DEM) of the surface geometries of MDF with 5-15 cm resolution, acquired along the Icelandic Rift zone using unmanned aerial vehicles (UAV). UAV provide a much higher resolution than aerial/satellite imagery and a much better overview than ground-based fieldwork, thus bridging the gap between outcrop scale and regional observations. 20Our data present representative outcrops of MDF, formed in basaltic sequences linked to the Mid Ocean Ridge. We acquired photosets of overlapping images along about 20 km of MDF and processed these using photogrammetry to create high resolution DEMs and ortho-rectified images. We use this dataset to map the faults and their damage zones to measure length, opening width and vertical offset of the faults and identify surface tilt in the damage zones. Ground truthing of the data was done by field observations. 25Mapped vertical offsets show typical trends of normal fault growth by segment coalescence. However, opening widths in mapview show variations at much higher frequency, caused by segmentation, collapsed relays and tilted blocks. These effects cause a commonly higher than expected ratio of vertical offset and opening width for a steep normal fault at depth.Based on field observations and the relationships of opening width and vertical offset, we define three endmember morphologies of MDF: (i) dilatant faults with opening width and vertical offset, (ii) tilted blocks (TB), and (iii) opening mode 30 (mode I) fissures. Field observation of normal faults without visible opening invariably shows that these have an opening filled by recent sediment. TB dominated normal faults tend to have a largest opening width with respect to vertical offsets. Fissures Opheim and Gudmundsson, 1989). The bedrock is mostly of volcanic origin with ages increasing with distance from the rift (Fig. 2). The succession of lava flows with cooling joints, paleo-soils and hyaloclastite result in locally complex mechanical stratigraphy. Faults and fissures crosscutting this mechanically heterogeneous section reactivate the pre-existing cooling joints close to the surface, leading to complex geometries (Forslund and Gudmundsson, 1991;Gudmundsson, 1987a; Gudmundsson 5 and Bäckström, 1991;Hatton et al., 1994).

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The stress pattern of Iceland

Cited by 47 publications

References 117 publications

Unstable Rifts, a Leaky Transform Zone and a Microplate: Analogues from South Iceland

Unstable Rifts, a Leaky Transform Zone and a Microplate: Analogues from South Iceland

Contemporary tectonic stress pattern of the Taranaki Basin, New Zealand

Structure of massively dilatant faults in Iceland: lessons learned from high resolution UAV data

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