Tilt Observations Around the KTB-Site / Germany: Monitoring and Modelling of Fluid Induced Deformation of the Upper Crust of the Earth
At the German Continental Deep Drilling site (KTB) the pilot borehole of a depth of 4000 m was used to inject water with a medium rate of 180 litres/minute over a period of one year. To monitor the expected surface deformation five borehole tiltmeters of the ASKANIA type Gbp10 were installed in the surrounding area of the KTB location in mid 2003. The deformation was detected at kilometre scale, together with the observations of induced seismicity in the area. We observed elastic as well as inelastic responses: changes of the rheologic properties due to pore pressure increase caused changes in the tidal parameters. First we quantified the expected additional drift for different injection scenarios at each tiltmeter site by numerical modelling. It could be demonstrated that for long term injection phases of up to four months a maximum tilt effect of about 40 nrad is modelled, which should be detectable. We expected changes of the drift curve, slow variations correlating with the injection rate as well as with changes of the rate.
First results of the monitoring are presented: they reveal a slight increase of the tidal parameters (main tidal constituent O1 and M2, north-south component) and drifts associated with the long-term injection. Comprehensive numerical modelling using the Finite Element software ABAQUS is in preparation.
KeywordsSurface tilt measurements fluid injection KTB drill hole ASKANIA tiltmeter tidal parameters upper Earth crust
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