Abstract:

 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.

Key words: lower crustal laminar flow, basinorogen coupling, thermal earthquake mechanism, prediction of strong earthquakes, the northeastern Tibetan Plateau