Spectral analysis was performed on a group of microseismic events (ML: -1.9 to -1.1) that occurred during a stimulation experiment at the Geothermal Resesearch Well GtGrSk4/05 in Germany. These events were recorded by a downhole 3-component sensor (natural frequency 15Hz, sampling rate 1000Hz) located in the accompanying borehole E GrSk 3/90 at 3800m depth, close (~500m) to the injection point. The seismicity level was very low and only 70 events were detected and located during an injection period of 6 days. They exhibited strong spatial and temporal clustering and mainly occurred towards the end of stimulation phases. Calculated source parameters provide the evidence for the dependence between the static stress drop and seismic moment as well as for scaling of apparent stress with seismic moment.

Vilnius, Lithuania