【摘要】 俯冲带作为地球循环体系的关键部位,具有构造活跃、地震多发以及地质条件复杂等特征。基于震源位置,俯冲带地震既可划分为板间和板内地震,也可分为浅源、中源和深源地震。俯冲带内的浅源地震包括板间地震和浅源板内地震,而中源和深源地震皆属于板内地震。在地球浅部,温度与压力低,浅源地震是由岩石发生脆性破裂或沿着先存断层发生不稳定摩擦滑移造成的。随着深度增加,温度和压力的增加使得流行于浅部的脆性和摩擦行为在无水条件下被强烈抑制,岩石从而表现为可抑制地震的韧性行为,使得中-深源地震的诱发机制有别于常规的脆性行为。随着研究的逐渐深入,人们了解到中源地震的诱发机制主要是脱水或与流体相关的致脆以及塑性剪切失稳,而深源地震的成因主要是相变致裂。然而,中-深源地震很可能是两种或两种以上机制共同作用的结果。例如,在中源深度既可能是流体相关的致脆导致脱水源区的脆性围岩产生地震,亦可能是脱水的蛇纹岩本身可能在流体孔隙压的作用下作粘滑滑移,而前者比后者更为重要。孕震带宽度大于"反裂隙模型"预测的亚稳态橄榄石冷核宽度的深源地震可能是由第一阶段的相变致裂和第二阶段的塑性剪切失稳诱发,而孕震带的实际宽度与预测宽度相当的深源地震则可能仅由相变致裂引起。只要过渡带内名义无水矿物中的结构水能释放出来,脱水致脆同样可能触发一些深源地震;而塑性剪切失稳不仅能在中-深源地震触发后的扩展阶段起着主导作用,而且还能单独触发一些中-深源地震,因此能够解释大多数反复发生的中-深源地震活动。更多还原

【Abstract】 As an important part of the Earths circulation system,subduction zone is characterized by active mountain building,high-frequency earthquakes,and complex geological conditions.Earthquakes in subduction zones can be divided into inter- and intra-plate categories in terms of the hypocenter relative to the subducting slab,or shallow-(0~60 km),intermediate-(60~300 km),and deep-(≥300 km) depth earthquakes according to focal depth.Shallow earthquakes include interplate earthquakes and shallow inland intraplate earthquakes while both intermediate- and deep-depth earthquakes are intraplate earthquakes.Shallow earthquakes are caused by cracking of intact rocks and factional sliding along the preexisting faults because the shallow part of the Earth stays at low temperatures and low pressures where rocks are dominated by brittle behavior.At greater depths,however,both temperature and pressure are high,so rocks deform by ductile flow because brittle and frictional behavior is suppressed unless fluids are present to help push open the cracks.Thus the origin of intermediate- and deep-depth earthquakes should be different from that of shallow events.Two important mechanisms of intermediate-depth earthquakes have been recognized;dehydration embrittlement and plastic shear instability.The origin of deep-depth earthquakes is still enigmatic but most likely caused by phase transition-induced faulting.However,not all of intermediate- and deep-depth earthquakes can be simply interpreted by a single mechanism as a combination of multiple mechanisms may act together in the initiation and propagation of the earthquakes.Intermediate-depth earthquakes,for example,may be produced by fluid-related embrittlement in brittle wall rocks and/or by stick—slip along dehydrating antigorite-rich fault zones,depending on the magnitude of effective confining pressure.The deep-depth earthquakes such as the 1994 Bolivia earthquake,whose seismogenic zones are much wider than the cold core of metastable olivine,as predicted by anticrack faulting model,could be initiated by phase transitioninduced faulting and then propagated by plastic shear instability.The deep-depth earthquakes such as the 2013 Okhotsk earthquake,whose seismogenic zones are as wide as the cold core,may result totally from phase transitioninduced faulting alone.If water in nominally anhydrous minerals(e.g.,olivine,wadesleyite,and ringwoodite)has released,dehydration embrittlement may also trigger deep-depth earthquakes in the transition zone.In contrast,plastic shear instability,which can make its own contribution to the propagation of deep earthquakes,is often responsible for most of repeating deep earthquakes.更多还原