High-resolution Seismic Investigations of a Geological Energy-storage Site - Dalby (Tornquist Zone), Southwest Sweden

Three high-resolution refraction and reflection seismic profiles for the planning of a major underground thermal-energy-storage site within the Tornquist suture zone of Scania in southwest of Sweden were acquired during August 2015. Combined cabled- and wireless recorders were used to provide continuity on both side of a major road running in the middle of the study area. First arrivals are clear in most shot gathers allowing them to be used for traditional refraction seismic data analysis and also for more advanced traveltime tomography. Bedrock depressions are clearly observed in the tomograms suggesting the possibility of weakness zones, highly fractured and/or weathered, in the bedrock and confirmed in several places by boreholes. Signs of reflections in raw shot gathers were encouraging and motivated to process the reflection component of the data. Several steeply-dipping reflections were imaged down to 400 m depth. The origins of the reflections are unclear right now ranging from amphibolite sheets to diabase dykes as well as faults within the gneissic rocks, and each of this implies a different geological scenario at where the site will be developed. This study however illustrates the potential of the combined refraction and reflection imaging for underground energy-storage-site characterizations.