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 - TY - JOUR A1 - Sudibyo, Maria R. P. A1 - Eibl, Eva P. S. A1 - Hainzl, Sebastian A1 - Hersir, Gylfi Páll T1 - Eruption Forecasting of Strokkur Geyser, Iceland, Using Permutation Entropy JF - Journal of geophysical research : Solid earth N2 - A volcanic eruption is usually preceded by seismic precursors, but their interpretation and use for forecasting the eruption onset time remain a challenge. A part of the eruptive processes in open conduits of volcanoes may be similar to those encountered in geysers. Since geysers erupt more often, they are useful sites for testing new forecasting methods. We tested the application of Permutation Entropy (PE) as a robust method to assess the complexity in seismic recordings of the Strokkur geyser, Iceland. Strokkur features several minute-long eruptive cycles, enabling us to verify in 63 recorded cycles whether PE behaves consistently from one eruption to the next one. We performed synthetic tests to understand the effect of different parameter settings in the PE calculation. Our application to Strokkur shows a distinct, repeating PE pattern consistent with previously identified phases in the eruptive cycle. We find a systematic increase in PE within the last 15 s before the eruption, indicating that an eruption will occur. We quantified the predictive power of PE, showing that PE performs better than seismic signal strength or quiescence when it comes to forecasting eruptions. KW - permutation entropy KW - forecasting KW - geyser KW - eruption KW - hydrothermal system; KW - volcano-seismology Y1 - 2022 U6 - https://doi.org/10.1029/2022JB024840 SN - 2169-9313 SN - 2169-9356 VL - 127 IS - 10 PB - American Geophysical Union CY - Washington ER - 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 - Eibl, Eva P. S. A1 - Hainzl, Sebastian A1 - Vesely, Nele I. K. A1 - Walter, Thomas R. A1 - Jousset, Philippe A1 - Hersir, Gylfi Pall A1 - Dahm, Torsten T1 - Eruption interval monitoring at strokkur Geyser, Iceland JF - Geophysical research letters N2 - Geysers are hot springs whose frequency of water eruptions remain poorly understood. We set up a local broadband seismic network for 1 year at Strokkur geyser, Iceland, and developed an unprecedented catalog of 73,466 eruptions. We detected 50,135 single eruptions but find that the geyser is also characterized by sets of up to six eruptions in quick succession. The number of single to sextuple eruptions exponentially decreased, while the mean waiting time after an eruption linearly increased (3.7 to 16.4 min). While secondary eruptions within double to sextuple eruptions have a smaller mean seismic amplitude, the amplitude of the first eruption is comparable for all eruption types. We statistically model the eruption frequency assuming discharges proportional to the eruption multiplicity and a constant probability for subsequent events within a multituple eruption. The waiting time after an eruption is predictable but not the type or amplitude of the next one.
Plain Language Summary Geysers are springs that often erupt in hot water fountains. They erupt more often than volcanoes but are quite similar. Nevertheless, it is poorly understood how often volcanoes and also geysers erupt. We created a list of 73,466 eruption times of Strokkur geyser, Iceland, from 1 year of seismic data. The geyser erupted one to six times in quick succession. We found 50,135 single eruptions but only 1 sextuple eruption, while the mean waiting time increased from 3.7 min after single eruptions to 16.4 min after sextuple eruptions. Mean amplitudes of each eruption type were higher for single eruptions, but all first eruptions in a succession were similar in height. Assuming a constant heat inflow at depth, we can predict the waiting time after an eruption but not the type or amplitude of the next one. Y1 - 2019 U6 - https://doi.org/10.1029/2019GL085266 SN - 0094-8276 SN - 1944-8007 VL - 47 IS - 1 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Eibl, Eva P. S. A1 - Müller, Daniel A1 - Walter, Thomas R. A1 - Allahbakhshi, Masoud A1 - Jousset, Philippe A1 - Hersir, Gylfi Páll A1 - Dahm, Torsten T1 - Eruptive cycle and bubble trap of Strokkur Geyser, Iceland JF - Journal of geophysical research : JGR. B: Solid earth N2 - The eruption frequency of geysers can be studied easily on the surface. However, details of the internal structure including possible water and gas filled chambers feeding eruptions and the driving mechanisms often remain elusive. We used a multidisciplinary network of seismometers, video cameras, water pressure sensors and one tiltmeter to study the eruptive cycle, internal structure, and mechanisms driving the eruptive cycle of Strokkur geyser in June 2018. An eruptive cycle at Strokkur always consists of four phases: (1) Eruption, (2) post-eruptive conduit refilling, (3) gas filling of the bubble trap, and (4) regular bubble collapse at shallow depth in the conduit. For a typical single eruption 19 +/- 4 bubble collapses occur in Phase 3 and 8 +/- 2 collapses in Phase 4 at a mean spacing of 1.52 +/- 0.29 and 24.5 +/- 5.9 s, respectively. These collapses release latent heat to the fluid in the bubble trap (Phase 3) and later to the fluid in the conduit (Phase 4). The latter eventually reaches thermodynamic conditions for an eruption. Single to sextuple eruptions have similar spacings between bubble collapses and are likely fed from the same bubble trap at 23.7 +/- 4.4 m depth, 13-23 m west of the conduit. However, the duration of the eruption and recharging phase linearly increases likely due to a larger water, gas and heat loss from the system. Our tremor data provides documented evidence for a bubble trap beneath a pool geyser. KW - bubble trap KW - eruptive cycle KW - geyser KW - hydrothermal systems KW - source KW - location KW - tremor Y1 - 2021 U6 - https://doi.org/10.1029/2020JB020769 SN - 2169-9313 SN - 2169-9356 VL - 126 IS - 4 PB - Wiley CY - Hoboken, NJ ER -