Ground Surface Response to Geothermal Drilling and the Following Counteractions in Staufen im Breisgau (Germany) Investigated by TerraSAR-X Time Series Analysis and Geophysical Modeling

The city of Staufen im Breisgau in southwest Germany suffers from a localized land uplift, which has occurred in the past six years in relation to geothermal drilling activities in 2007. So far, severe damages at 269 buildings have been recorded. The chemical transformation of anhydrite and water to gypsum, resulting in a volume increase, has been attributed as the cause of the uplift. Previous studies provide knowledge on the spatio-temporal displacement evolution from 2008 through 2011 using leveling and spaceborne Synthetic Aperture Radar Interferometry (InSAR) measurements, but lack a detailed representation of vertical and horizontal displacement contributions as well as geophysical modeling. This study focuses not only on continued observation analysis from June 2011 through July 2013, but also on obtaining and evaluating horizontal displacements in Staufen based on combined analysis of TerraSAR-X satellite imagery from both ascending and descending orbits. Applying the Small BAseline Subset (SBAS) approach a deceleration of annual cumulative line of sight (LOS) uplift is observable from 13.8 cm ± 0.3 cm (July 2008–July 2009) to 3 cm ± 0.3 cm (July 2012–July 2013) within area of maximum deformation NNE of the drilling zone. Conducting displacement decomposition on ascending and descending data of a common period (October 2012 through July 2013) yields in an approximately symmetric eastand westward motion with maximum values approximately 1 cm and 1.4 cm, respectively. The joint inversion of ascending and OPEN ACCESS Remote Sens. 2014, 6 10572 descending InSAR data for the common period from October 2012 through July 2013 shows that a horizontal rectangular source with length, width and depth of 177 m ± 19 m, 69 m ± 15 m and 89 m ± 9 m, respectively, can satisfactorily model the observation. The amount of opening at depth shows a decrease in time by about 71% for the period 2011–2012 as compared to period 2008–2009.