Articles | Volume 17, issue 12
https://doi.org/10.5194/nhess-17-2335-2017
https://doi.org/10.5194/nhess-17-2335-2017
Research article
 | 
19 Dec 2017
Research article |  | 19 Dec 2017

Structural analysis of S-wave seismics around an urban sinkhole: evidence of enhanced dissolution in a strike-slip fault zone

Sonja H. Wadas, David C. Tanner, Ulrich Polom, and Charlotte M. Krawczyk

Abstract. In November 2010, a large sinkhole opened up in the urban area of Schmalkalden, Germany. To determine the key factors which benefited the development of this collapse structure and therefore the dissolution, we carried out several shear-wave reflection-seismic profiles around the sinkhole. In the seismic sections we see evidence of the Mesozoic tectonic movement in the form of a NW–SE striking, dextral strike-slip fault, known as the Heßleser Fault, which faulted and fractured the subsurface below the town. The strike-slip faulting created a zone of small blocks ( < 100 m in size), around which steep-dipping normal faults, reverse faults and a dense fracture network serve as fluid pathways for the artesian-confined groundwater. The faults also acted as barriers for horizontal groundwater flow perpendicular to the fault planes. Instead groundwater flows along the faults which serve as conduits and forms cavities in the Permian deposits below ca. 60 m depth. Mass movements and the resulting cavities lead to the formation of sinkholes and dissolution-induced depressions. Since the processes are still ongoing, the occurrence of a new sinkhole cannot be ruled out. This case study demonstrates how S-wave seismics can characterize a sinkhole and, together with geological information, can be used to study the processes that result in sinkhole formation, such as a near-surface fault zone located in soluble rocks. The more complex the fault geometry and interaction between faults, the more prone an area is to sinkhole occurrence.

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Short summary
In 2010 a sinkhole opened up in the urban area of Schmalkalden, Germany. Shear-wave reflection seismic profiles were carried out around the sinkhole to investigate the reasons for the collapse. A strike-slip fault and a fracture network were identified that serve as fluid pathways for water-leaching soluble rocks near the surface. The more complex the fault geometry and interaction between faults, the more prone an area is to sinkhole occurrence.
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