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

Abstract

[1] 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.

Seismohydrological effects related to the NW Bohemia earthquake swarms of 2000 and 2008: Similarities and distinctions

“…An updoming of the lithosphere-asthenosphere boundary below 9 the Cheb Basin ( 14 For more than two decades, the complicated processes of swarmquake generation have been 15 discussed in a broad framework. Simplified, three main triggering mechanisms have been Due to the high mobility of CO 2 dominated fluids below the Cheb Basin, a complex interaction 21 of these triggering mechanisms is likely in the Vogtland/NW Bohemia region. 22 Since 1985/86, the most frequent epicentre zone of the NW Bohemia earthquakes has been near earthquake swarms that occurred in 1997 and 2000 , gas flow and groundwater level anomalies 5 had been recorded at the Seismohydrological Observatory of the Saxon Academy of Sciences at 6 Bad Brambach, 10 km W of Nový Kostel (Fig 1).…”

“…The Table 1 gives an overview of the origin of the analysed seismic data and the other subsequently 19 used basic parameters including their temporal resolution. For the comparison of the temporal 20 and spatial behaviour of the earthquake swarms and their relation to the hydrological anomalies, 21 seismic events with local magnitudes of M L > -1 within the Nový Kostel area were used, in 22 each case, between September and April 2000-01 as well as 2008-09 ( Fig. 2-6).…”

Microseismicity induced during fluid-injection: A case study from the geothermal site at Groß Schönebeck, North German Basin

“…They attributed it to the lower pressure build-up and increased transmissivity of the fault system. Jahr et al (2008) of water was injected. High seismicity rate was observed almost instantaneously with the start of injection, except when the target area had been stimulated during previous injections (Charléty et al, 2007).…”

Natural and man-made induced hydrological signals, detected by high resolution tilt observations at the Geodynamic Observatory Moxa/Germany

“…The toroidal and some spheroidal modes were also observed with high quality by the tiltmeter array at the super deep drilling site KTB (Jentzsch et al, 2005; comp. Jahr et al, 2008). …”

“…due to ocean tides can affect the tilt signals in the milliarcsecond range (Zschau, 1976;Baker, 1980). However, induced tilt effects can also be caused by artificial sources, like pumping, injection Kümpel et al, 2006;Jahr et al, 2008) or man-made loadings, e.g. filling of a reservoir (Jentzsch and Koß, 1997).…”