Imaging the 2010-2011 Inflationary Source at Krysuvik, SW Iceland, Using Time-Dependent Vp/Vs Tomography

Abstract

Near Reykjavik, the capital of Iceland, lies the Krysuvik high-temperature geothermal area, which could potentially provide vast amounts of energy to this and surrounding towns and villages. Possible changes to the heat-source and/or hydrothermal system in this area are indicated by a period of surface deformation between 2007 and 2016 (Gudjonsdottir et al., 2018). This study provides subsurface images below Krysuvik and the neighboring areas with high resolution down to 10 km depth using 15 years of earthquake data. These images indicate regions of partial-melt and a large super-critical reservoir below ~5 km depth, which would serve well as a fluid source for a new power-plant. The robustness of this model is assessed using time-dependent seismic tomography. Through systematic study of known issues with time-dependent seismic tomography, it is shown that significant changes do occur in the results on time-scales comparable to the surface deformation. Changes that we assess and suggest are significant beyond e.g. the influence of differences in ray-path geometries and travel-time errors. Several hypotheses are developed based on these results and available information from multiple disciplines. Based on this integration of information with our results, the most likely explanations of the surface deformation signal are: 1) strong degassing of a magmatic source due to increased heat from deeper magmatic infiltration, and 2) bending and subsequent fracturing of an impermeable barrier by expanding fluids.