德国大陆超深钻井注水诱发地震的精确定位
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摘要
2000年8月21日～10月20日,德国大陆超深钻井(KTB)进行了为期60天的新一轮注水诱发地震实验.在对KTB台网所记录到的2 700多次地震的原始波形进行分析和处理的基础上,对其中的237次地震进行了精确定位.定位时,先采用和达法剔除了误识的非KTB诱发地震事件;然后,使用大折刀法求得了台站偏差的最佳值,以及中误差和平均误差;最后应用Geiger法进行修定,从而保证了237个事件定位的中误差达到0.1 km的高精度.定位结果显示,在大于9.3 km(几乎是主井底的深度)没有发生诱发地震.这一现象表明,在这个深度,应力可能低于摩擦强度,以至于由注水引起的孔隙压力的变化不足以诱发地震;在这样的深度不存在可渗透的、取向恰当的断层.这个深度也可能是这一区域内的地震活动性的最大深度,即在这一相对稳定地区的板块内部,主井底已接近脆-延性转换带.并用实验室的结果和超深钻井中所观测到的热流值资料解释了这一现象.
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). More than 2 700 events were recorded by the KTB seismic network. Among them 237 events were of high signal-to-noise ratio, and were processed and acurately located. When the events were located, non KTB events were weeded out by Watatis method. The standard deviation, mean and median were obtained by Jackknifes technique, and finally the events were accurately located by Geigers 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 explantion is that at such depths the stress levels may not close to the rocks 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.
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). More than 2 700 events were recorded by the KTB seismic network. Among them 237 events were of high signal-to-noise ratio, and were processed and acurately located. When the events were located, non KTB events were weeded out by Watatis method. The standard deviation, mean and median were obtained by Jackknifes technique, and finally the events were accurately located by Geigers 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 explantion is that at such depths the stress levels may not close to the rocks 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.
引文
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GeigerL.1912.Probability method for the determination of earthquake epicenter from the arrival time only[J].BullStLouisUni,8:60～71
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HarjesH-P,BramK,DuerbaumH-J, et al.1997.Origin and nature of crustal reflections: results from integrated seismic measurements at theKTB superdeep drilling site[J].J GeophysRes,102(B8):18267～18288
DahlhaimH-A,GebrandeH,SchmedesE, et al.1997.Seismicity and stress field in the vicinity of theKTB location[J].J GeophysRes,102(B8):18293～18506
JostM L,BuesselbergT,JostO,et al.1998.Source parameters of injection-induced microearthquakes at9 km depth at theKTB deep drilling siteGermany[J].BullSeismSocAmer,88(3):815～832
MeissnerR,StrehlauJ.1982.Limits of stresses in the continental crusts and their relation to the depth-frequency distribution of shallow earthquakes[J].Tectonics,1:173～189
SibsonR H.1982.Fault zones models,heat flow, and the depth distribution of earthquake in the continental crust of theUnitedStates[J].BullSeismSocAmer,72:151～163
SmithR B,BruhnR L.1984.Intraplate extensional tectonics of the easternBasin-Range:Inferences on structureal style from seismic reflection data regional tectonics,and thermal-mechanical models of the brittle-ductile deformation[J].J GeophysRes,89:5733～5762
TichelaarB W,RuffL J.1989.How good are our best models?[J].Eos,TransAmerGeophysUnion,70(20):593WangerG A,CoyleD A,DuysterJ, et al.1997.Post-Variscan thermal and tectonic evolution ofKTB site and its surroundings[J].J GeophysRes,102(B8):18221～18232
ZobackM D,HarjesH-P.1997.Injection-induced earthquake and crustal stress at9 km depth at theKTB deep drilling site,Germany[J].J GeophysRes,102(B8):18477～18491
BrudyM,ZobackM D,FuchsK,et al.1997.Estimation of the complete stress tensor to8 km depth in theKTB scientific drill holes:Implications for crustal strength[J].J GeophysRes,102(B8):18453～18475
ClauserC.1997.The thermal regime of the crystalline continental crust:Implications from theKTB[J].J GeophysRes,102(B8):18417～18441
EmmermannR,LauterjungJ.1997.TheGerman continental deep drilling programKTB: overview and major results[J].J GeophysRes,102(B8):18179～18201
GeigerL.1912.Probability method for the determination of earthquake epicenter from the arrival time only[J].BullStLouisUni,8:60～71
HaakV.1997.Introduction to special section:TheKTB deep drill hole[J].J GeophysRes,102:18175～18177
HarjesH-P,BramK,DuerbaumH-J, et al.1997.Origin and nature of crustal reflections: results from integrated seismic measurements at theKTB superdeep drilling site[J].J GeophysRes,102(B8):18267～18288
DahlhaimH-A,GebrandeH,SchmedesE, et al.1997.Seismicity and stress field in the vicinity of theKTB location[J].J GeophysRes,102(B8):18293～18506
JostM L,BuesselbergT,JostO,et al.1998.Source parameters of injection-induced microearthquakes at9 km depth at theKTB deep drilling siteGermany[J].BullSeismSocAmer,88(3):815～832
MeissnerR,StrehlauJ.1982.Limits of stresses in the continental crusts and their relation to the depth-frequency distribution of shallow earthquakes[J].Tectonics,1:173～189
SibsonR H.1982.Fault zones models,heat flow, and the depth distribution of earthquake in the continental crust of theUnitedStates[J].BullSeismSocAmer,72:151～163
SmithR B,BruhnR L.1984.Intraplate extensional tectonics of the easternBasin-Range:Inferences on structureal style from seismic reflection data regional tectonics,and thermal-mechanical models of the brittle-ductile deformation[J].J GeophysRes,89:5733～5762
TichelaarB W,RuffL J.1989.How good are our best models?[J].Eos,TransAmerGeophysUnion,70(20):593WangerG A,CoyleD A,DuysterJ, et al.1997.Post-Variscan thermal and tectonic evolution ofKTB site and its surroundings[J].J GeophysRes,102(B8):18221～18232
ZobackM D,HarjesH-P.1997.Injection-induced earthquake and crustal stress at9 km depth at theKTB deep drilling site,Germany[J].J GeophysRes,102(B8):18477～18491
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