应力扰动对断层摩擦声发射活动影响的实验研究
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摘要
利用中尺度岩石摩擦实验开展了应力扰动对断层摩擦滑动过程中声发射活动影响的实验研究,据此讨论同震应力变化引起的小震活动特征及其预测意义。实验结果表明方波状应力扰动对粘滑失稳前的声发射活动有明显影响,即触发了一些声发射事件,使得粘滑发生前声发射活动增强并使出现的时间提前。这种影响随平均正应力的提高和扰动振幅的增大而增强,其中剪应力扰动(增加)比正应力扰动(减小)对声发射活动的影响更明显。从统计角度,未叠加应力扰动时声发射事件一般开始在临近粘滑前应力积累达～90%以上时;叠加应力扰动后声发射事件提前至应力积累达到～70%时,甚至更早。结果意味着同震应力变化能否对区域内的强震活动产生显著影响主要取决于断层的绝对应力是否已临近失稳强度。而小震活动的变化能够在一定程度上反映断层的应力状态,因此综合考虑同震应力变化和小震活动分析强震危险性更为合理。同时也需充分考虑其中的不确定性。
Effects of stress perturbation on acoustic emission(AE) during fault friction are studied by using medium-scale experiments of rock friction,and the characteristics of seismicity caused by coseismic stress change and its implication in earthquake forecasting are discussed based on the experimental results.The experiments indicate that stress perturbation of square wave can obviously affect AE activity,it can trigger some AE events so that AE activity before stick-slip becomes stronger and occurs earlier.The effect increases with increasing average normal stress and perturbation amplitude,and perturbation effect from shear stress(increase) is more evident than that from normal stress(decrease).In statistics,when stress perturbation is not applied,AE events usually occur just before stick-slip even if there are AE events,i.e.occurring when stress accumulation reaches above ~90%.When stress perturbation is applied,AE events occur earlier before stick-slip,i.e.occurring when stress accumulation reaches ~70% and even much earlier.The experimental results mean that whether the coseismic stress change caused by a strong earthquake can obviously affect strong seismic activity in its neighbour area,it is mainly depentent on if the absolute stress of faults comes close to instablity strength.Small earthquaks can reflect stress state of fault at certain extend,therefore,it is more reasonable to analyze earthquake potential by combing coseismic stress change and activity of small events.However,the uncertainty existing in the process should also be considered.
Effects of stress perturbation on acoustic emission(AE) during fault friction are studied by using medium-scale experiments of rock friction,and the characteristics of seismicity caused by coseismic stress change and its implication in earthquake forecasting are discussed based on the experimental results.The experiments indicate that stress perturbation of square wave can obviously affect AE activity,it can trigger some AE events so that AE activity before stick-slip becomes stronger and occurs earlier.The effect increases with increasing average normal stress and perturbation amplitude,and perturbation effect from shear stress(increase) is more evident than that from normal stress(decrease).In statistics,when stress perturbation is not applied,AE events usually occur just before stick-slip even if there are AE events,i.e.occurring when stress accumulation reaches above ~90%.When stress perturbation is applied,AE events occur earlier before stick-slip,i.e.occurring when stress accumulation reaches ~70% and even much earlier.The experimental results mean that whether the coseismic stress change caused by a strong earthquake can obviously affect strong seismic activity in its neighbour area,it is mainly depentent on if the absolute stress of faults comes close to instablity strength.Small earthquaks can reflect stress state of fault at certain extend,therefore,it is more reasonable to analyze earthquake potential by combing coseismic stress change and activity of small events.However,the uncertainty existing in the process should also be considered.
引文
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[15]刘力强,马胜利,马瑾,等.岩石构造对声发射统计特征的影响[J].地震地质,1999,21(4):377-386.
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[18]黄元敏,马胜利,缪阿丽,等.剪切载荷扰动对断层摩擦影响的实验研究[J].地震地质,2008,31(2):276-286.
[19]刘力强,马胜利,马瑾,等.不同结构岩石标本声发射b值和频谱的时间扫描及其物理意义[J].地震地质,2001,23(4):481-492.
[2]Nalbant S S,Hubert A,King G C P.Stress coupling betweenearthquakes in northwest Turkey and the north Aegean Sea[J].J.Geophys.Res.,1998,103:24469-24486.
[3]Stein R S,Barka A A,Dieterich J H.Progressive failure onthe North Anatolian fault since 1939by earthquake stress trig-gering[J].Geophys.J.Int.,1997,128:594-604.
[4]King G C P,Stein R S,Lin J.Static stress changes and thetriggering of earthquakes[J].Bull.Seismol.Soc.Am.,1994,84:935-953.
[5]Hardebeck J L,Nazareth J J,Hauksson E.The static stresschange triggering model:constraints from two southern Cali-fornia aftershock sequences[J].J.Geophys.Res.,1998,103:24427-24437.
[6]Stein R S.The role of stress transfer in earthquake occurrence[J].Nature,1999,402:605-609.
[7]万永革,沈正康,兰从欣.根据走滑大地震前后应力轴偏转和应力降求取偏应力量值的研究[J].地球物理学报,2006,49(3):838-844.
[8]万永革.根据大地震前后应力轴偏转和应力降求取应力量值的研究[J].地震学报,2006,28(5):472-477.
[9]Nishimura N,Toda S,Stein R S,et al.Forecasting the evolu-tion of seismicity in southern California:Animations built onearthquake stress transfer[J].J.Geophys.Res.,2005,B05S16,doi:10.1029/2004JB003415.
[10]Toda S,Lin J,Meghraoui M,et al.12May 2008 M=7.9Wenchuan,China,earthquake calculated to increase failurestress and seismicity rate on three major fault systems[J].J.Geophys.Res.,35,2008,L17305,doi:10.1029/2008GL034903.
[11]Parsons T,Ji C,Kirby E.Stress changes from the 2008Wenchuan earthquake and increased hazard in the Sichuanbasin[J].Nature,2008,454:509-510.
[12]张国宏,单新建,李卫东.汶川MS8.0地震库伦破裂应力变化及断层危险性初步研究[J].地震地质,2008,30(4):935-944.
[13]万永革,沈正康,盛书中,等.2008年汶川大地震对周围断层的影响[J].地震学报,2009,31(2):128-139.
[14]单斌,熊熊,郑勇,等.2008年5月12日Mw7.9汶川地震导致的周边断层应力变化[J].中国科学D辑,2009,39(5):537-545.
[15]刘力强,马胜利,马瑾,等.岩石构造对声发射统计特征的影响[J].地震地质,1999,21(4):377-386.
[16]Locker D A,Beeler N M.Premonitory slip and tidal trigge-ring of earthquakes[J].J.Geophys.Res.,1999,104:20133-20151.
[17]崔永权,马胜利,刘力强.应力扰动对断层摩擦影响的实验研究[J].地震地质,2005,27(4):645-652.
[18]黄元敏,马胜利,缪阿丽,等.剪切载荷扰动对断层摩擦影响的实验研究[J].地震地质,2008,31(2):276-286.
[19]刘力强,马胜利,马瑾,等.不同结构岩石标本声发射b值和频谱的时间扫描及其物理意义[J].地震地质,2001,23(4):481-492.
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