Strike‐slip faulting during the 2014 Bárðarbunga‐Holuhraun dike intrusion, central Iceland

Abstract

Over a 13 day period magma propagated laterally from the subglacial Bárðarbunga volcano in the northern rift zone, Iceland. It created > 30,000 earthquakes at 5–7 km depth along a 48 km path before erupting on 29 August 2014. The seismicity, which tracked the dike propagation, advanced in short bursts at 0.3–4.7 km/h separated by pauses of up to 81 h. During each surge forward, seismicity behind the dike tip dropped. Moment tensor solutions from the leading edge show exclusively left‐lateral strike‐slip faulting subparallel to the advancing dike tip, releasing accumulated strain deficit in the brittle layer of the rift zone. Behind the leading edge, both left‐ and right‐lateral strike‐slip earthquakes are observed. The lack of non‐double‐couple earthquakes implies that the dike opening was aseismic.

High-Resolution Digital Elevation Modeling from TLS and UAV Campaign Reveals Structural Complexity at the 2014/2015 Holuhraun Eruption Site, Iceland

“…We observed a non-uniform spatial distribution of strike-slip and opening mode components, as well as the presence of both left-lateral and right-lateral fault components, among which the former is dominant. Therefore, these results agree with those of seismic (Agustsdottir et al, 2016), geodetic and structural field studies (Ruch et al, 2016). Preexisting topography, earlier fault locations and the locations of eruption sites close to that of an eruption in 1797/98 produced highly variable transtensional displacement with primarily leftlateral strike-slip indicators.…”

“…In transtensional regions located close to the main eruption site, 81% of faults contain left-lateral components, 17% contain right-lateral components, and 2% do not exhibit clear strikeslip components. These results are in agreement with those of independent studies (Agustsdottir et al, 2016), as they reflect the presence of both left-lateral and right-lateral transtensional components at the surface, which Agustsdottir et al (2016) observed at depth.…”

“…Petrologic data and seismic records obtained by the Icelandic Meteorological Office (Figure 1B) suggest that the ascent of magma beneath the Bardarbunga central volcano was followed by the lateral transport of magma through the upper crust over a distance of ∼45 km to the Holuhraun eruption site (Sigmundsson et al, 2015;Geiger et al, 2016). Based on the analysis of seismic data, this lateral magma propagation was associated with normal faulting, as well as strike-slip faulting at variable depths (Agustsdottir et al, 2016). Seismic records reflect the presence of dominantly left-lateral slip components, as well as some right-lateral slip components (Agustsdottir et al, 2016); a relatively high number of right-lateral seismic events occurred close to the Holuhraun eruption site in the north, at depths of 5-8 km.…”

“…Based on the analysis of seismic data, this lateral magma propagation was associated with normal faulting, as well as strike-slip faulting at variable depths (Agustsdottir et al, 2016). Seismic records reflect the presence of dominantly left-lateral slip components, as well as some right-lateral slip components (Agustsdottir et al, 2016); a relatively high number of right-lateral seismic events occurred close to the Holuhraun eruption site in the north, at depths of 5-8 km. Geodetic and field surveys revealed that dominantly left-lateral slip and only minor right-lateral slip occurred prior to the onset of the main eruption on 29th August 2014 (Ruch et al, 2016).…”

Tremor-rich shallow dyke formation followed by silent magma flow at Bárðarbunga in Iceland

“…Our rates are slightly lower than the rates observed elsewhere 15;28 30 and are non-steady state. These interpretations nd further support in the following observations: (i) most dyke related seismicity was in the 5 to 8 km depth range according to results from the IMO permanent network 10 and a temporary, more dense network 15 . However, shallowing seismicity at less than 5 km depth was observed around C1 and C2 before August 27 th ( gure 1 and 15 ).…”