Geophysical processes and biosphere: article

Аnnotation: The comparative characteristics of seismic and deformational effects of the three great subduction megaearthquakes in Sumatra in 2004 (Mw = 9.2), Maule, Chile in 2010 (Mw = 8.8) and Tohoku, Japan in 2011 (Mw = 9.0) were taken into consideration. In all cases the main rupture at the time of the earthquake was located in the zone of subduction, on the hollow plunging lithospheric plate beneath a continent or island arc. The process of destruction of each focus was characterized by megathrust, with a gentle inclination angle (8-18º), according to the definitions of the focal mechanism, in almost full compliance with a gentle dipping of subducted lithospheric plate. The rupture occurred in a locked area of subducting plate extended on several kilometers below the ocean bottom to a depth of 30-40 km. In all three cases, the maximum coseismic slip, set according to geodetic measurements, occurred in the upper 25 km of the blocked area, whereas the lower part of the site radiated coherent short-period seisms. The trace of the rupture on the surface, marked by the area of the aftershock, ranged from 400-600 km in the case of Tohoku in 2011 and Maule in 2010 earthquakes, and up to ~1500 km in the Sumatran earthquake in 2004. The reason for such significant differences may lie in the geometry of the subduction zone and the presence of the strength barriers at opposite ends of the rupture. The rupture in earthquake Maule and Tohoku was bilateral with an approximately symmetric distribution relative to the epicenter, while in the Sumatran earthquake rupture extended unilaterally relative to the epicenter from the South-East to North-West. Varied and the propagation time of the rupture. If in the first two cases, it was up to 140-160 sec, for the Sumatra earthquake it lasted an unusually long time to 500-600 sec. Turned out to be the most tsunamigenic earthquake in Tohoku in 2011 with the height of tsunami waves up to 60 m on the coast of the province Sanriku stretching over 200 km. The rupture in megaearthquakes is not limited to depth first of the locked seismogenic area, labelled by aftershock area and maximum coseismic slip installed at the geodetic GPS measurements. The rupture continues aseismicity (postseismic slip) in the transition zone from brittle to brittle-plastic slip to depths of ~60-80 km. In addition, there is evidence that displacement on surface megathrust can continue more deeply in the region of brittle-plastic slip, which can be evidence of observations in the southwestern Japan and southern Chile episodic slow slip events («silent», or «slow» earthquakes) and «seismic tremor». These differences in seismic and deformation manifestations can serve as evidence of the change of frictional properties with depth along the surface of megathrust. It should also be recognized that the strength barriers, asperity and holes on the surface of megathrust expressed in specific geological structures or unclear nature of parts of high frequency radiation, can be significantly diversified the seismic manifestations in the time of great subduction megaearthquakes.