东昆仑、玉树、汶川地震的发生规律和形成机理:兼论大陆地震成因与预测

The regularity and mechanism of East Kunlun,Wenchuan,and Yushu earthquakes and discussion on genesis and prediction of continental earthquakes.

青藏高原东北部东昆仑、汶川、玉树等强震的同震地表破裂不对称发育,伴随余震有规律地分别向东、南东和北北东方向迁移,很可能是源于恒河盆地流经亚东、当雄、安多、库赛湖、治多、玉树、甘孜、汶川的弧形下地壳"热河"的流速和流向变化形成的,下地壳热流物质正在向云南及邻区汇聚形成下地壳"热海",导致长时间跨季度构造热干旱,其影响超过大气环流的作用。地表破裂不一定受断层控制,震源也不在断层面上,下地壳流动导致中地壳发震并进一步影响上地壳形成同震脆性破裂系统。大陆板内盆山过渡带地震密集,大陆板内地震是在下地壳层流的热动力作用下导致活动地壳分层变形的产物。在大陆盆山耦合、圈层耦合的非线性开放系统中,从大洋底部的软流圈层流进入大陆底部使得地幔软流圈加厚,底辟上升为大陆下地壳流动,为地震活动提供了巨量热能;热软化的下地壳缓慢的韧性流动孕育了大陆板内地震;中地壳韧-脆性剪切带易于积累能量,发生热能与应变能的转化,产生地震,形成震源层;上地壳脆性断层活动和地表破裂是地震释放深部能量的载体和方式之一。地壳稳定性评价的依据应当是地壳的活动性而不是断层的活动性。大陆活动构造区地震活跃期与平静期交替实际上是下地壳地震能量的聚散过程,体现在下地壳热主导的韧性流动构造与上地壳应力主导的脆性破裂构造之间的相互作用。下地壳热软化物质流动过程中流速、流向等突然改变触发地震,并产生共振波。大陆下地壳流层在厚度、温度、粘度、流速、流向上的变化产生一定程度的温度异常、流体异常及与其相关的大气层、电场、磁场、重力场、地球化学场、应力场、应变场、生物场等异常。合理布置天空网、地面网、地下网,综合立体监测有效的地震前兆,系统地开展长期、中期和短临地震预测,能够不断地提高地震预测水平。

Asymmetrical co-seismic surface ruptures and aftershock sequences of East Kunlun,Wenchuan,and Yushu strong earthquake in the northeastern Tibetan Plateau propagated eastward,southeastward and northeastward,respectively.These earthquakes may generally be related to the variation in flow velocity and flow direction of the arc lower crustal ＂thermal river＂ that originates from Ganges Basin and flows through Yadong,Damxung,Amdo,Kusai Lake,Zhidoi,Ganzi,Wenchuan toward Yunnan province and its adjacent areas forming a lower crustal ＂thermal sea＂,which caused a 10-month mega tectonic drought.The co-seismic surface ruptures did not precisely coincide with faults,and hypocenters did not precisely occur on brittle faults.Lower crustal flow controlled seismic sources in middle crust and then caused brittle fracture system in upper crust.Strong earthquake swarms often occurred on the basin-orogen boundary.Continental intraplate earthquakes were product of stratification deformation of active crust driven by lower crustal laminar flow.In opening non-linear complex system of basin-orogen coupling and different sphere and layer coupling in continent,uprising of a thickened continental mantle asthenosphere diapir flowed laterally from ocean provided huge thermal energy for lower crustal flow and earthquake;slow ductile flow of thermal softening lower crust gestated earthquakes;in the ductile-brittle shear zone of middle crust,it is easy to accumulate energy and the conversion from thermal energy to strain energy occurred there,leading to earthquakes and forming the hypocenter layer;the brittle fault in upper crust and surface rupture only are one of carriers and ways of releasing the deeper crustal energy.The regional crustal stability assessment should be based on the active crust instead of active fault.The abrupt variation in flow velocity and flow direction of lower crust triggered earthquakes causing resonant wave.Alternation of earthquake quiet period and active period actually is the accumulating and releasing process of lower crustal energy,which is exhibited as the interaction between ductile flow tectonics of lower crust and brittle fracture system of upper crust.The variation in thickness,temperature,viscosity,velocity and direction of lower crustal flow layer and ＂river＂ causes characteristic thermal anomaly and fluid anomaly,and related anomalies of atmosphere,electricity,magnetism,gravity,geochemistry,stress,strain,and animal.Space-surface-underground monitoring system for valid earthquake precursors will raise the level of strong earthquake prediction.