Monitoring changes of the reflection response of the SE2 shear zone due to fluid injection into the KTB pilot borehole by an active seismic reflection experiment

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In the KTB pilot borehole an extensive fluid injection experiment is scheduled for April 2004 and will last for about 12 months. The injection will take place in the openhole section of the borehole at a depth of about 4000m. At that depth the borehole intersects a major crustal shear zone, the SE2 reflector. The proposal aims at exploiting this unique opportunity in order to study the influence of pore pressure fluctuations and fluid mobility on the reflection response of seismic signals by means of an active seismic reflection survey. Highly reproducible seismic signals will be generated using the P-wave vibrator of the GGA-Institute. The signals will be recorded by a permanently installed 3C-geophone array. Depending on the injection cycle the signals will be several times repeated in order to monitor the expected variations of the reflecion response. The analysis of the time-dependent reflection responses will be the final stage of the project. The results will provide the basis for further conclusions, like for instance an evaluation of the practicability of conshore crustal time-lapse surveys, a further understanding of the physics of the seismogenic process, or studies relating to the seismic imaging of effective-stress related changes of elastic properties within shear zones.