TY  - JOUR
A1  - Greenfield, Tim
A1  - Winder, Tom
A1  - Rawlinson, Nicholas
A1  - Maclennan, John
A1  - White, Robert S.
A1  - Ágústsdóttir, Thorbjörg
A1  - Bacon, Conor Andrew
A1  - Brandsdóttir, Bryndis
A1  - Eibl, Eva P. S.
A1  - Glastonbury-Southern, Esme
A1  - Gudnason, Egill Árni
A1  - Hersir, Gylfi Páll
A1  - Horálek, Josef
T1  - Deep long period seismicity preceding and during the 2021 Fagradalsfjall eruption, Iceland
JF  - Bulletin of volcanology : official journal of the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI)
N2  - We use a dense seismic network on the Reykjanes Peninsula, Iceland, to image a group of earthquakes at 10-12 km depth, 2 km north-east of 2021 Fagradalsfjall eruption site. These deep earthquakes have a lower frequency content compared to earthquakes located in the upper, brittle crust and are similar to deep long period (DLP) seismicity observed at other volcanoes in Iceland and around the world. We observed several swarms of DLP earthquakes between the start of the study period (June 2020) and the initiation of the 3-week-long dyke intrusion that preceded the eruption in March 2021. During the eruption, DLP earthquake swarms returned 1 km SW of their original location during periods when the discharge rate or fountaining style of the eruption changed. The DLP seismicity is therefore likely to be linked to the magma plumbing system beneath Fagradalsfjall. However, the DLP seismicity occurred similar to 5 km shallower than where petrological modelling places the near-Moho magma storage region in which the Fagradalsfjall lava was stored. We suggest that the DLP seismicity was triggered by the exsolution of CO2-rich fluids or the movement of magma at a barrier to the transport of melt in the lower crust. Increased flux through the magma plumbing system during the eruption likely adds to the complexity of the melt migration process, thus causing further DLP seismicity, despite a contemporaneous magma channel to the surface.
KW  - deep long-period earthquakes
KW  - magma plumbing system
KW  - Iceland
KW  - Reykjanes
KW  - low-frequency
KW  - Fagradalsfjall
Y1  - 2022
U6  - https://doi.org/10.1007/s00445-022-01603-2
SN  - 0258-8900
SN  - 1432-0819
VL  - 84
IS  - 12
PB  - Springer
CY  - Berlin ; Heidelberg ; New York
ER  - 
TY  - JOUR
A1  - Ziegler, Moritz O.
A1  - Rajabi, Mojtaba
A1  - Heidbach, Oliver
A1  - Hersir, Gylfi Pall
A1  - Agustsson, Kristjan
A1  - Arnadottir, Sigurveig
A1  - Zang, Arno
T1  - The stress pattern of Iceland
JF  - Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth
N2  - Iceland is located on the Mid-Atlantic Ridge which is the plate boundary between the Eurasian and the North American plates. It is one of the few places on earth where an active spreading centre is located onshore but the stress pattern has not been extensively investigated so far. In this paper we present a comprehensive compilation of the orientation of maximum horizontal stress (S-Hmax). In particular we interpret borehole breakouts and drilling induced fractures from borehole image logs in 57 geothermal wells onshore Iceland. The borehole results are combined with other stress indicators including earthquake focal mechanism solutions, geological information and overcoring measurements resulting in a dataset with 495 data records for the S-Hmax orientation. The reliability of each indicator is assessed according to the quality criteria of the World Stress Map project The majority of S-Hmax orientation data records in Iceland is derived from earthquake focal mechanism solutions (35%) and geological fault slip inversions (26%). 20% of the data are borehole related stress indicators. In addition minor shares of S-Hmax orientations are compiled, amongst others, from focal mechanism inversions and the alignment of fissure eruptions. The results show that the S-Hmax orientations derived from different depths and stress indicators are consistent with each other.
 The resulting pattern of the present-day stress in Iceland has four distinct subsets of S-Hmax orientations. The S-Hmax orientation is parallel to the rift axes in the vicinity of the active spreading regions. It changes from NE-SW in the South to approximately N-S in central Iceland and NNW-SSE in the North. In the Westfjords which is located far away from the ridge the regional S-Hmax rotates and is parallel to the plate motion. (C) 2016 Elsevier B.V. All rights reserved.
KW  - Iceland
KW  - Stress field
KW  - Stress pattern
KW  - Borehole image logs
Y1  - 2016
U6  - https://doi.org/10.1016/j.tecto.2016.02.008
SN  - 0040-1951
SN  - 1879-3266
VL  - 674
SP  - 101
EP  - 113
PB  - Elsevier
CY  - Amsterdam
ER  -