Seismicity and Multi-Scale Imaging of the Krafla Volcano, Northeastern Iceland

Left : Two cross-sections through the Krafla caldera showing the Vp/Vs ratio of the velocity models alongside the formation temperatures measured in the boreholes. Areas A1, B1/B2, and C1/C2 are interpreted respectively as liquid, steam, and potential magma zones.

A recent study combines two seismic networks, a widespread permanent network and a dense temporary one, to improve earthquake localization and internal imaging of the Krafla volcano.

Local earthquake tomography enabled the construction of high-resolution P- and S-wave velocity models, revealing that velocity variations are mainly linked to permeability, fluid saturation, and fluid phase, rather than solely to lithology.

Two distinct upflow zones of boiling fluids, with varying steam-to-liquid ratios, were identified in the eastern and western geothermal fields, separated by a cooler, more permeable structure. These zones are fueled by magmatic heat sources, confirmed by the discovery of magma during deep drilling.

This combination of geological structures and fluids creates a patchy, dynamic environment along the fault, controlling where and how the fault slips, sometimes smoothly, sometimes suddenly.

Cette combinaison de structures géologiques et de fluides crée un environnement hétérogène et dynamique le long de la faille, contrôlant les lieux et les modes de glissement, parfois progressifs, parfois soudains.

The full study is published in JGR Solid Earth