The accurate location of the injection-induced microearthquakes in German Continental Deep Drilling Program
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From August 21, 2000 to October 20, 2000 a fluid injection-induced seismicity experiment has been carried out in the KTB (German Continental Deep Drilling Program). The KTB seismic network recorded more than 2 700 events. Among them 237 events were of high signal-to-noise ratio, and were processed and accurately located. When the events were located, non KTB events were weeded out by Wadati’s method. The standard deviation, mean and median were obtained by Jackknife’s technique, and finally the events were accurately located by Geiger’s method so that the mean error is about 0.1 km. No earthquakes with focal depth greater than 9.3 km, which is nearly at the bottom of the hole, were detected. One of the explanation is that at such depths the stress levels may not close to the rock’s frictional strength so that failure could not be induced by the relatively small perturbation in pore pressure. Or at these depths there may be no permeable, well-oriented faults. This depth may be in close proximity to the bottom of the hole to the brittle-ductile transition, even in this relatively stable interior of the interaplate. This phenomenon is explained by the experimental results and geothermal data from the superdeep borehole.
Key wordsscientific deep drilling fluid-injection induced seismicity earthquake location Jackknife method brittle-ductile transition
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