Interlobate esker architecture and related hydrogeological features derived from a combination of high-resolution reflection seismics and refraction tomography, Virttaankangas, southwest Finland

Abstract

A novel high-resolution (2-4 m source and receiver spacing) reflection and refraction seismic survey was carried out for aquifer characterization and to confirm the existing depositional model of the interlobate esker of Virttaankangas, which is part of the Säkylänharju-Virttaankangas glaciofluvial esker-chain complex in southwest Finland. The interlobate esker complex hosting the managed aquifer recharge (MAR) plant is the source of the entire water supply for the city of Turku and its surrounding municipalities. An accurate delineation of the aquifer is therefore critical for long-term MAR planning and sustainable use of the esker resources. Moreover, an additional target was to resolve the poorly known stratigraphy of the 70-100-m-thick glacial deposits overlying a zone of fractured bedrock. Bedrock surface as well as fracture zones were confirmed through combined reflection seismic and refraction tomography results and further validated against existing borehole information. The highresolution seismic data proved successful in accurately delineating the esker cores and revealing complex stratigraphy from fan lobes to kettle holes, providing valuable information for potential new pumping wells. This study illustrates the potential of geophysical methods for fast and cost-effective esker studies, in particular the digital-based landstreamer and its combination with geophone-based wireless recorders, where the cover sediments are reasonably thick.

High‐resolution reflection seismics reveal the structure and the evolution of the Quaternary glacial Tannwald Basin

“…Maries et al . () showed seismic facies of arched geometry and high amplitudes as well as dimensions of 100 m length and 20 m height, which is comparable to the eskers that we found in profile 3. The eskers described by Maries et al .…”

“…The eskers described by Maries et al . () appear to be more elongated (250 m) than in our sections, however this is probably because of the oblique cut, with regard to an assumed main ice flow direction toward the north. Pugin et al .…”

“…; Maries et al . ) due to their coarse‐grained composition. Due to their position at the base of the over‐deepened valley they are presumably less affected by surface pollutants than shallower aquifers.…”

Estimation of groundwater storage from seismic data using deep learning

“…; Maries et al . ). For each sample, we compute seismic responses from multiple source locations and couple simulations with deep learning for the prediction of water‐table level and the amount of stored water.…”

“…We use a Gaussian process to generate samples from the potential scenarios for the aquifer for both the material model and the geometry. The prior information for the aquifer system is based on earlier studies and traditional ray-tracingbased estimates (Artimo et al 2003;Maries et al 2017). For each sample, we compute seismic responses from multiple source locations and couple simulations with deep learning for the prediction of water-table level and the amount of stored water.…”