Scattering and Absorption Imaging of the Hengill High-Temperature Geothermal Area, Southwest Iceland

Abstract

We applied 3D scattering and absorption imaging to the Hengill volcanic area (southwest Iceland), where high-enthalpy geothermal reservoirs are presently harnessed. These techniques have shown the potential for detecting magmatic intrusions and fluid reservoirs in volcanic regions. Here, we target seismic scattering and absorption as proxies of the elastic and anelastic properties of the crust to understand their potential in areas of geothermal energy extraction. The harnessed Nesjavellir geothermal field was used as a benchmark to extend interpretation into non-harnessed areas and provide better insight when evaluating exploitable geo-resources. Shallow, high-scattering anomalies mark the sub-vertical Hengill fissure swarm. Deeper low-scattering volumes likely highlight sub-horizontal magmatic intrusions beneath the Hengill central volcano, whose less fractured volume acts as a barrier for the surrounding seismicity. At Nesjavellir, high absorption co-located with high scattering volumes spatially correlates with previously detected high Vp/Vs volumes, suggesting the existence of fluid- and/or melt-filled complex seismically active networks of faults and fractures. Our results suggest the presence of geothermal reservoirs in non-harnessed areas (Mosfellsheiði and Ölkelduháls) shown by similar high-absorption anomalies at depths comparable with the Nesjavellir geothermal resource. Scattering and absorption imaging complement more standard imaging techniques, improving interpretation in geothermal resource exploration.