Publication Date
April 2018
Abstract
Subrosion can result in depressions and sinkholes, which are a geohazard. To improve the knowledge of subrosion processes, high-resolution geophysical imaging and a detailed characterization of subsurface structures are required. One of the main subrosion areas in Germany is along the Kyffhäuser-Southern-Margin-Fault (KSMF) in Thuringia. Two shear wave (SH) reflection seismic profiles of 300 m length in total were carried out along two sinkholes. The near-surface down to ca. 100 m depth was imaged with a resolution of less than 1 m down to 15 m depth and a resolution of 1 m to 3 m at 50 m depth. The internal structures of the leached anhydrite and gypsum were imaged. The reflection patterns indicate a heterogeneous near-surface geology around the sinkholes, with mainly lateral and vertical variations of discontinuous reflectors and small-scale fractures, which are necessary for percolation of meteoric water and sinkhole development, especially in areas with a deep groundwater table and no faults. This is the case for one of the two sinkholes. The other is located at a fault with a shallow groundwater table at 37 m depth. The sinkhole margins are characterized by reflectors, which dip towards the focal points of the sinkholes. Previous sinkholes probably generated fractures, which act as additional fluid pathways. As a result, a collapse can be triggered more easily. Indicators for continued collapse are observed in the profile of the fracture-induced sinkhole by the continued migration of focal points of consecutive collapse events over time.
Rights Information
DOI
https://doi.org/10.5038/9780991000982.1003
Sinkhole Imaging and Identification of Fractures with SH-wave Reflection Seismic
Subrosion can result in depressions and sinkholes, which are a geohazard. To improve the knowledge of subrosion processes, high-resolution geophysical imaging and a detailed characterization of subsurface structures are required. One of the main subrosion areas in Germany is along the Kyffhäuser-Southern-Margin-Fault (KSMF) in Thuringia. Two shear wave (SH) reflection seismic profiles of 300 m length in total were carried out along two sinkholes. The near-surface down to ca. 100 m depth was imaged with a resolution of less than 1 m down to 15 m depth and a resolution of 1 m to 3 m at 50 m depth. The internal structures of the leached anhydrite and gypsum were imaged. The reflection patterns indicate a heterogeneous near-surface geology around the sinkholes, with mainly lateral and vertical variations of discontinuous reflectors and small-scale fractures, which are necessary for percolation of meteoric water and sinkhole development, especially in areas with a deep groundwater table and no faults. This is the case for one of the two sinkholes. The other is located at a fault with a shallow groundwater table at 37 m depth. The sinkhole margins are characterized by reflectors, which dip towards the focal points of the sinkholes. Previous sinkholes probably generated fractures, which act as additional fluid pathways. As a result, a collapse can be triggered more easily. Indicators for continued collapse are observed in the profile of the fracture-induced sinkhole by the continued migration of focal points of consecutive collapse events over time.
