Time-lapse Seismics in Crystalline Crust – Lessons Learned at the Continental Deep Drilling Site – KTB

We conducted an active seismic experiment with the aim to measure changes in seismic reflection amplitudes as a consequence of fresh water injection and corresponding pressure changes in the SE2 fault zone at the German Continental Deep Drilling site (KTB). The injection took place at the bottom of the 4-km-deep pilot borehole in crystalline rock units between 2004 and 2005. Prior to the experiment, theoretical calculations indicated a possible increase in the PP reflection coefficient of about 15% for vertical incidence, as a result of an injection-induced reduction of the seismic velocities within the fault zone. Although the principal objective of the experiment (i.e. the direct detection of amplitude changes) was not reached, some important aspects for the design of time-lapse seismic experiments in crystalline environments have been learned and will be presented.