Deformation, seismicity, and fluids: Results of the 2004/2005 water injection experiment at the KTB/Germany

Abstract

During the past decades, the research into fluid‐controlled geodynamic processes in the upper crust of the Earth is put foreward regarding the stress accumulation, deformation, and seismicity. In a large‐scale injection experiment at the deep borehole site KTB (Kontinentale Tiefbohrung der Bundesrepublik Deutschland) in Germany, more than 84.000 m 3 fresh water was injected in 4000 m depth over 10 months, and a lot of geoscientific investigations were connected to this injection test. The pore‐pressure change of more than 10 MPa yielded an induced deformation, which was detected by a tiltmeter array. The used five borehole tiltmeters of the ASKANIA type with a resolution of better than 1 nrad belong to the most sensitive tiltmeters worldwide. The poro‐elastic finite‐element modeling used for the interpretation of the observed tilts revealed an uplift of 3.1 mm above the injection point. Furthermore, it was shown that the induced stress and deformation fields depend mainly on the fluids inside the fault zones, particularly the SE2‐reflector which is the Franconian fault zone, and the local Nottersdorf fault: While the maximum pore pressure is concentrated close to the injection point at the SE2 zone, the maximum deformation of about 3 cm is located at the intersection line of both faults in 4 km depth. The area of the modeled maximum deformation is highly correlated with the region of the observed induced seismicity, thus linking seismicity and deformation. The connection of tilt observation and modeling provides a useful tool for the investigation of fluid coupled geoprocesses.