首页|Geomechanical interpretation of induced seismicity observed at Basel geothermal reservoir
Geomechanical interpretation of induced seismicity observed at Basel geothermal reservoir
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Some of the induced seismic events had moment magnitude exceeded 2。0 at the hydraulicstimulation in Basel， Switzerland in 2006 and they were felt by the population in the town。 Theauthors analyzed seismic data including the large events observed during and after the hydraulicstimulation。 We investigated the fundamental characteristics of the large events and have found thatthere are considerable differences in the characteristics of the large events by their hypocentrallocation and origin time。 Based on previous results， we also estimated critical pore pressure for shearslip， which is considered as one of the triggers of the shear slip on existing fracture planes， using theinformation of the stress state。 It has been revealed that many of the large events occurred with therelatively small increase in the pore pressure。 These observations suggest that the large events werenot triggered simply by the increase of the pore pressure。 Following this observation， we investigatedthe effect of the stress redistribution induced by the other preceding events。 We calculated static stresschanges caused by the shear slip of the seismic events using the information of fault plane and sourceparameters。 The results from the calculation showed that there was stress change which conduced tofailure on the fault plane of the largest events。 However， we did not observe any significant stresschanges before the occurrence of the largest events and the magnitude of the stress change was quitesmaller than the increase of the pore pressure。 We hence concluded that static stress change inducedby the shear slip of the preceding seismic events did not trigger the shear slip of the existing fracture。The other phenomena to redistribute the stress， including thermal effect and volumetric change ofrock mass should be considered in our future study。
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