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Changes in groundwater chemistry before and after earthquakes
in northern Iceland
by Margareta Andrén
Date and time: Thursday, December 11 at 10.00
Place: U26, Geohuset (link to the house plan)
Chemical changes in groundwater before and after earthquakes in northern Iceland are reported in this study and mechanisms whereby these occur are proposed. Earthquakes are common in northern Iceland along the Tjörnes Fracture Zone (TFZ), a transform zone, linking the Northern Volcanic Zone (NVZ) to the Kolbeinsey Ridge north of Iceland. Hafralækur is situated in the Tjörnes Fracture Zone where groundwater has been sampled on a weekly basis since September 2008. In the first paper we report changes in stable isotope ratios (δ2H) and concentrations of cations (Na, K, Ca and Si) in Hafralækur preceding two earthquakes M>5 in October 2012 and April 2013 (Skelton et al., 2014). In the second manuscript we compare analyses of groundwater from the 100 m deep borehole with analyses of drill cuttings from an adjacent borehole. There is a stepwise decrease of major elements with depth probably due to different lava flows. Thin sections (grain mounts) are used for identifying minerals and to estimate mineral abundances at different depths. XRD-peaks for clay minerals are identified at most depths. Zeolites are abundant around water inlets and as pseudomorphs of plagioclase. From replacement textures, we infer that chemical changes in groundwater before earthquakes were caused by cation release during constant volume replacement of plagioclase by zeolites and that chemical changes after earthquakes were caused by cation uptake during zeolite formation in vesicles.
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