During the 1991 episode, two 50 hours hydraulic injection tests were carried out at the bottom of the well GPK1 ( https://cdgp.u-strasbg.fr/geonetwork/srv/fre/catalog.search#/metadata/SSF-GPK 1). The fresh water was injected at a flowrate of 7 l/s during the first test and 15 l/s during the second test. New seismic probes composed of 3-axis accelerometers built by the CSM (Camborne School of Mines) monitored the induced seismicity. Two of them were deployed in new recovered wells 4550 ( https://cdgp.u-strasbg.fr/geonetwork/srv/fre/catalog.search#/metadata/SSF-4550 ) and 4601 ( https://cdgp.u-strasbg.fr/geonetwork/srv/fre/catalog.search#/metadata/SSF-460 1). In addition, two hydrophones were installed in a new borehole EPS1 ( https://cdgp.u-strasbg.fr/geonetwork/srv/fre/catalog.search#/metadata/SSF-EPS 1), drilled in 1990 and sited at about 600m SSE of GPK1. The network permitted to detect more than 400 induced seismic events during the two tests of the episode. About 60% of them were located.

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.