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  • 1.
    Andrén, Margareta
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Stockmann, Gabrielle
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Skelton, Alasdair
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Sturkell, Erik
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Guðrúnardóttir, Helga Rakel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Keller, Nicole Simone
    Odling, Nic
    Dahrén, Börje
    Broman, Curt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Balic-Zunic, Tonci
    Hjartarson, Hreinn
    Siegmund, Heike
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Freund, Friedemann
    Kockum, Ingrid
    Coupling between mineral reactions, chemical changes in groundwater, and earthquakes in Iceland2016Inngår i: Journal of Geophysical Research - Solid Earth, ISSN 2169-9313, E-ISSN 2169-9356, Vol. 121, nr 4, s. 2315-2337Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Chemical analysis of groundwater samples collected from a borehole at Hafralaekur, northern Iceland, from October 2008 to June 2015 revealed (1) a long-term decrease in concentration of Si and Na and (2) an abrupt increase in concentration of Na before each of two consecutive M 5 earthquakes which occurred in 2012 and 2013, both 76km from Hafralaekur. Based on a geochemical (major elements and stable isotopes), petrological, and mineralogical study of drill cuttings taken from an adjacent borehole, we are able to show that (1) the long-term decrease in concentration of Si and Na was caused by constant volume replacement of labradorite by analcime coupled with precipitation of zeolites in vesicles and along fractures and (2) the abrupt increase of Na concentration before the first earthquake records a switchover to nonstoichiometric dissolution of analcime with preferential release of Na into groundwater. We attribute decay of the Na peaks, which followed and coincided with each earthquake to uptake of Na along fractured or porous boundaries between labradorite and analcime crystals. Possible causes of these Na peaks are an increase of reactive surface area caused by fracturing or a shift from chemical equilibrium caused by mixing between groundwater components. Both could have been triggered by preseismic dilation, which was also inferred in a previous study by Skelton et al. (2014). The mechanism behind preseismic dilation so far from the focus of an earthquake remains unknown.

  • 2.
    Skelton, Alasdair
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Liljedahl-Claesson, L.
    Wästeby, Niklas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Andrén, Margareta
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Stockmann, G.
    Sturkell, E.
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Stefansson, A.
    Tollefsen, Elin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Siegmund, Heike
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Keller, N.
    Kjartansdóttir, R.
    Hjartarson, H.
    Kockum, I.
    Hydrochemical Changes Before and After Earthquakes Based on Long-Term Measurements of Multiple Parameters at Two Sites in Northern IcelandA Review2019Inngår i: Journal of Geophysical Research - Solid Earth, ISSN 2169-9313, E-ISSN 2169-9356, Vol. 124, nr 3, s. 2702-2720Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Hydrochemical changes before and after earthquakes have been reported for over 50years. However, few reports provide sufficient data for an association to be verified statistically. Also, no mechanism has been proposed to explain why hydrochemical changes are observed far from earthquake foci where associated strains are small (<10(-8)). Here we address these challenges based on time series of multiple hydrochemical parameters from two sites in northern Iceland. We report hydrochemical changes before and after M >5 earthquakes in 2002, 2012, and 2013. The longevity of the time series (10 and 16years) permits statistical verification of coupling between hydrochemical changes and earthquakes. We used a Student t test to find significant hydrochemical changes and a binomial test to confirm association with earthquakes. Probable association was confirmed for preseismic changes based on five parameters (Na, Si, K, O-18, and H-2) and postseismic changes based on eight parameters (Ca, Na, Si, Cl, F, SO4, O-18, and H-2). Using concentration ratios and stable isotope values, we showed that (1) gradual preseismic changes were caused by source mixing, which resulted in a shift from equilibrium and triggered water-rock interaction; (2) postseismic changes were caused by rapid source mixing; and (3) longer-term hydrochemical changes were caused by source mixing and mineral growth. Because hydrochemical changes occur at small earthquake-related strains, we attribute source mixing and water-rock interaction to microscale fracturing. Because fracture density and size scale inversely, we infer that mixing of nearby sources and water-rock interaction are feasible responses to small earthquake-related strains. Plain Language Summary Changes in groundwater chemistry before and after earthquakes have been reported for over 50years. However, few studies have been able to prove that the earthquakes caused these changes. Also, no study has explained why these changes are often reported far from where the earthquake occurred. Here we address these challenges based on measurements of groundwater chemistry made at two sites in northern Iceland over time periods of 10 and 16years. We used statistical methods to prove that the earthquakes caused changes of ground water chemistry both before and after the earthquakes. We showed that changes of groundwater chemistry before earthquakes were caused by slow mixing between different groundwaters, which triggered reactions with the wall rock that changed groundwater chemistry, and that changes of groundwater chemistry after earthquakes were causes by rapid mixing between different groundwaters. That these changes were detected far from where the earthquakes occurred suggests that cracking of the wall rock at a very small scale was all that was needed for mixing of different groundwaters and reactions with the wall rock to occur.

  • 3.
    Skelton, Alasdair
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Löwhagen, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Fairchild, Ian J.
    Boyce, Adrian
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Siegmund, Heike
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Webster, David
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Spencer, Anthony M.
    Stable isotopes of oxygen and hydrogen in meteoric water during the Cryogenian Period2019Inngår i: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 320, s. 253-260Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We measured delta O-18 and delta H-2 values of muscovite and carbonate mineral separates from metamorphosed carbonate -bearing mudstone layers in late Tonian to early Cryogenian strata, including Sturtian glacial deposits, which were deposited in a coastal setting at an approximate paleolatitude of 30-35 degrees S and now crop out on Islay and the Garvellach Islands, Scotland. From these values, we calculated delta O-18 and delta H-2 values of meteoric water that equilibrated with clay at diagenetic conditions which we infer were reached shortly after deposition (i.e. before the end of the Cryogenian Period) because sediment accumulation was rapid due to fast subsidence at that time. This calculation required removal of the effects of exchange with reservoir rocks, metamorphic volatilization and mixing with metamorphic fluids on delta O-18 and delta H-2 values. The values we calculated for meteoric water fall within the 2 sigma ranges delta O-18 = 1 to -4 parts per thousand and delta H-2 = 0 to -23-parts per thousand, respectively. These ranges are similar to present day values at equivalent latitudes. This finding is consistent with sediment accumulation in the Cryogenian Period having occurred in a climate similar to present day (Ice Age) conditions. This conclusion is not at odds with the Snowball Earth hypothesis because one of its predictions is that sediment accumulation occurred as the climate warmed at the end of panglaciation, a prediction supported by sedimentological evidence of multiple glacial advances and retreats in our study area and elsewhere.

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