The Hot Dry Rock (HDR) site of Soultz-sous-Forêts in Alsace was chosen in 1986 for scientific investigations. During the first phase of the project (1987-1988), a first borehole GPK1 ( https://cdgp.u-strasbg.fr/geonetwork/srv/fre/catalog.search#/metadata/SSF-GPK 1) was drilled. It reached a final depth of 2000 m and various investigations were undertaken during that period. In December 1988, an injection test was made at the bottom zone of this borehole with a relatively low flow rate of 3.3 l/s for a period of three days. Induced seismicity recorded was detected by 3-axis geophone probes deployed in three old recovered oil wells at depth ranging from 850 to 1350 m. A small amount of the detected seismicity could be located and showed a trend to grow towards greater depths than the injection zone.

The following report from BRGM in the link gives details about the experiments and presents the results about the seismic monitoring and the location of the events. Some hydraulic data are presented as well with figures.