Joint Project SIMULTAN - Sinkhole Characterization and Monitoring with Supplementing Geophysical Methods

The joint project SIMULTAN (Sinkhole Instability: integrated MULTi-scale monitoring and ANalysis) develops and applies an early recognition system of sinkhole instability, unrest and collapse in Germany. The research approach combines structural, geodetic, geophysical, petrophysical, and hydrogeological mapping methods, accompanied by sensor development, multi-scale monitoring, modelling, and an information platform. Two focus areas are investigated in Germany, for which sinkhole unrest has been identified. The surveyed areas are representative of evaporitic sinkhole formation, and are highly relevant since located in densely populated areas. Shear-wave reflection seismics enables high-resolution structural imaging of critical zones, while additional vertical seismic profiling (VSP) provides hints on subrosive zones by velocity analyses. Spatial detection thresholds for microseismic events were calculated using a combination of synthetic event signals and noise recorded in the field. Improvements of the detection and localization capability due to additional borehole stations and surface mini-arrays were investigated. The potential to detect mass dislocations in the upper subsurface is proven by repeated gravimetry and levelling campaigns, that are supplemented by micro-gravimetry. How combined direct-push and SIP-monitoring will characterize sufficiently the soil-water-interaction in the upper 40 m is still in the testing phase, but stable inversion schemes are yielded. All these petrophysical parameters are fed into modelling and simulation studies that describe dissolution initiation and explain realistic collapse scenarios in the light of overburden strength. These shall support decision processes, and the cooperation with geological surveys will advance the development of sinkhole instability recognition systems.