FD Modelling of Deeply-Buried Paleo-Dolines underneath the City of Munich
A. Sell, H. Buness, J. Ziesch, D. Tanner and A. Weller
Event name: 1st Conference on Geophysics for Geothermal and Renewable Energy Storage
Session: Poster: Geophysical Methods for Geothermal Utilization III
Publication date: 10 September 2019
Info: Extended abstract, PDF ( 934.62Kb )
Price: € 20
We used FD-seismic modelling to investigate paleo-doline structures in the Upper Jurassic (Malm) carbonates in the Bavarian Molasse Basin at a depth of 2 – 3 km. A high-quality 3-D seismic dataset that was shot for an area-wide supply of the district heating system of Munich shows distinct paleo-dolines, which could be isolated as geo-bodies in a variance volume. They show a vertical extent up to 500 m, while their diameter increases, from top to bottom, up to 750 m. The largest structures are connected with faults. The results of the modelling show that diffractions occur at the edges of the doline that interfere with reflections of deeper reflectors. Regardless of the migration algorithm used (including depth migration using the correct velocity model), these interferences could not be separated. Therefore distortions remain that were previously interpreted as the true extent of the dolines. In addition, we could show that the form of the dolines most likely resemble a bowl-shaped structure rather than a trapeze shape, and that the velocities are reduced inside and/or directly beneath the dolines, which causes down¬bending of deeper reflectors. The results confirm that dolines in the Malm carbonates represents a promising target for geothermal energy extraction.