Dynamics of dyke intrusion in the mid-crust of Iceland

White, R. S.; Drew, Julian; Martens, H. R.; Key, Janet; Soosalu, Heidi; Jakobsdóttir, Steinunn S.

doi:10.1016/j.epsl.2011.02.038

Cited by 144 publications

(129 citation statements)

References 42 publications

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“…The deep crustal earthquakes are located in distinct regions, beneath Kollóttadyngja shield volcano to the north, beneath the hyaloclastite mountain Upptyppingar to the east, location of a dyke intrusion in -2008White et al, 2011), and beneath Askja volcano, attributed to melt migration (Soosalu et al, 2010;Key et al, 2011;Greenfield and White, 2015).…”

Section: Seismicitymentioning

confidence: 99%

Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath

Schöpa¹,

Chao²,

Lipovsky³

et al. 2017

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Abstract. Using data from a network of 58 seismic stations, we characterise a large landslide that occurred at the southeastern corner of the Askja caldera, Iceland, on 21 July 2014, including its precursory tremor and mass wasting aftermath. Our study is motivated by the need for deeper generic understanding of the processes operating not only at the time of catastrophic slope failure, but also in the preparatory phase and during the transient into the subsequent stable state.In addition, it is prompted by the high hazard potential of the steep caldera lake walls at Askja as tsunami waves created by 15 the landslide reached famous tourist spots 60 m above the lake level. Since direct observations of the event are lacking, the seismic data give valuable details on the dynamics of this landslide episode. The excellent seismic data quality and coverage of the stations of the Askja network made it possible to jointly analyse the long-and short-period signals of the landslide to obtain information about the triggering, initiation, timing, and propagation of the slide. The seismic signal analysis and a landslide force history inversion of the long-period seismic signals showed that the Askja landslide was a single, large event 20starting at the SE corner of the caldera lake at 23:24:05 UTC and propagating to the NW in the following 2 min. The bulk sliding mass was 7-16×10 10 kg, equivalent to a collapsed volume of 35-80×10 6 m 3 , and the centre of mass was displaced horizontally downslope by 1260±250 m during landsliding. The seismic records of stations up to 30 km away from the landslide source area show a tremor signal that started 30 min before the main landslide failure. It is harmonic, with a fundamental frequency of 2.5 Hz and shows time-dependent changes of its frequency content. We attribute the complex 25 tremor signal to accelerating and decelerating stick-slip motion on failure planes at the base and the sides of the landslide body. The accelerating motion culminated in aseismic slip of the landslide visible as a drop in the seismic amplitudes down to the background noise level 2 min before the landslide high-energy signal begins. We propose that the seismic signal of the precursory tremor may be developed as an indicator for landslide early-warning systems. The 8 hours after the main landslide failure are characterised by smaller slope failures originating from the destabilised caldera wall decaying in 30 frequency and magnitude. We introduce the term afterslides for this subsequent, declining slope activity after a large landslide.Earth Surf. Dynam. Discuss., https://doi

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Section: Seismicitymentioning

confidence: 99%

Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath

Schöpa¹,

Chao²,

Lipovsky³

et al. 2017

Preprint

Self Cite

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“…Such flip of focal mechanisms over a short time period was seen in the Upptyppingar swarm in 2007 in Iceland, northeast of the glacier (Jakobsdóttir et al, 2008;White et al, 2011). Substantial changes in rotation of focal solutions were mainly observed immediately prior to the eruption (approximately 15 h before its onset) and during the first days of the eruption from 30th of September to 2nd of October).…”

Section: Occurrence Of the State Of Stress And Geometrical Rotations mentioning

confidence: 96%

“…Also, both tectonic regimes occurred spatially in close proximity to each other, so no particular distribution was observed. This feature was also highlighted in the Upptyppingar swarm (Jakobsdóttir et al, 2008;White et al, 2011). However, then the location of the maximum amount of rotation seemed to be located northern of the Barðarbunga volcano where the main shock occurred, and in an ice-free domain ( Figure 13B).…”

Section: Occurrence Of the State Of Stress And Geometrical Rotations mentioning

confidence: 97%

“…Deviated states of stress from both the regional stress field and during the volcanic crisis show similar stress orientations and stress shape ratio (i.e., σ 1 ≈ σ 2 ). White et al (2011) have demonstrated that the flip of normal to reverse focal mechanisms may occur within a minute and in the same location. The two opposite states of stress characterized by the strike-slip regime that were highlighted during the volcanic crisis in 1996 support the same observation of two opposite fracturing mechanisms.…”

Section: State Of Stress During the 1996 Eruptionmentioning

confidence: 99%

“…This stress field results from volcanic, tectonic processes and isostasic rebound of the crust. Episodic volcanic crises may also cause local high diversity of focal mechanisms with time (e.g., Einarsson, 1991;Roman et al, 2008;White et al, 2011). Thus, a second stress analysis was carried out to evaluate the state of stress during a volcanic crisis and the results were compared to the regional stress field.…”

Section: Introductionmentioning

confidence: 99%

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Volcano-tectonic interactions revealed by inversion of focal mechanisms: stress field insight around and beneath the VatnajÃ¶kull ice cap in Iceland

et al. 2014

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Volcano-tectonic processes in the central part of Iceland, covered by the Vatnajökull glacier, are investigated by inversion of focal mechanisms. Working on a large catalog of focal mechanisms determined by the Icelandic Meteorological Office (IMO), we used a damped regional-scale stress inversion method to obtain an insight of kilometric variations of the stress field. To evaluate the resolution and the stability of this stress field solution, we computed checkerboard tests, stress field models and error propagation tests. Stress field models showed a continuous stress regime between normal and strike-slip faulting, associated with a high stress shape ratio (i.e., σ 1 ≈ σ 2 ). Two main directions of σ hmin were evidenced: the first one was in agreement with the regional spreading direction of Iceland and the second one was deviated, being almost perpendicular to the first one. The deviated stress direction is sustained through the 20 year time-span of the study around the Bárðarbunga and Grimsvötn central volcanoes while the spreading direction remains predominant around the Hamarinn volcano. This result supports the hypothesis that this volcano lacks collapse caldera and shares a fissure swarm with the larger Bárðarbunga volcano. On a smaller temporal scale, during the 1996 volcanic crisis, a bimodal distribution of σ hmin showed two opposite strike-slip regimes where the deviated direction dominated. Because these two states of stress T1 and T2 show stress regimes away from the Andersonian positions, P, B, and T axes, the rapid flip between these two regimes may be associated with the progressive melt intrusion of a dyke.

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Stress changes, focal mechanisms, and earthquake scaling laws for the 2000 dike at Miyakejima (Japan)

et al. 2015

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Faulting processes in volcanic areas result from a complex interaction of pressurized fluid-filled cracks and conduits with the host rock and local and regional tectonic setting. Often, volcanic seismicity is difficult to decipher in terms of the physical processes involved, and there is a need for models relating the mechanics of volcanic sources to observations. Here we use focal mechanism data of the energetic swarm induced by the 2000 dike intrusion at Miyakejima (Izu Archipelago, Japan), to study the relation between the 3-D dike-induced stresses and the characteristics of the seismicity. We perform a clustering analysis on the focal mechanism (FM) solutions and relate them to the dike stress field and to the scaling relationships of the earthquakes. We find that the strike and rake angles of the FMs are strongly correlated and cluster on bands in a strike-rake plot. We suggest that this is consistent with optimally oriented faults according to the expected pattern of Coulomb stress changes. We calculate the frequency-size distribution of the clustered sets finding that focal mechanisms with a large strike-slip component are consistent with the Gutenberg-Richter relation with a b value of about 1. Conversely, events with large normal faulting components deviate from the Gutenberg-Richter distribution with a marked roll-off on its right-hand tail, suggesting a lack of large-magnitude events (M w > 5.5). This may result from the interplay of the limited thickness and lower rock strength of the layer of rock above the dike, where normal faulting is expected, and lower stress levels linked to the faulting style and low confining pressure.

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Dynamics of dyke intrusion in the mid-crust of Iceland

Cited by 144 publications

References 42 publications

Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath

Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath

Volcano-tectonic interactions revealed by inversion of focal mechanisms: stress field insight around and beneath the VatnajÃ¶kull ice cap in Iceland

Stress changes, focal mechanisms, and earthquake scaling laws for the 2000 dike at Miyakejima (Japan)

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