Characterisation of a Fault System at 4km Depth Using Induced Microseismicity – The German Deep Drilling Site (KTB)

摘要

We investigate microseismicity induced during a long-term water injection experiment at the German Deep Drilling Site (KTB) in 2004/2005. Precise location of the events shows, that the seismicity was induced in a NW-SE trending band, which is shifted from the injection source towards NE. The band correlates with a zone of enhanced seismic reflectivity and pertains to the SE2 fracture system. A value of 0.02m^2/s for the hydraulic diffusivity is estimated from the distribution of induced events. The dominant fault mechanism is reverse faulting, with the P axis parallel to the direction of the local maximum horizontal stress. Some events show oblique reverse faulting, while the third group of events is reverse faulting with a differing fault strike direction. Our findings are more compatible with a thrust-fault regime than a strike-slip regime, which is postulated from the stress tensor estimate in the KTB drilling hole. The seismicity does not occur along the major NW-SE trending, NE dipping faults of the SE2 system, but on favourably oriented smaller fracture planes and bends of the SE2.