The Impact On The Northeast And North China Caused By The Tohoku-Oki Earthquake In Japan In2011

The11March2011Mw9.0Tohoku-Oki earthquake occurred off the east coast ofnorthern Honshu of Japan in the Pacific Ocean, which is the fourth largest earthquakesince modern instrumental recordings. The coseismic displacement observationsindicated a maximum permanent eastward movement of5.3m, accompanied with asubsidence up to1.1m on the coastal line of the Tohoku region. And this earthquakealso produced horizontal coseismic displacements up to35mm in Northeast andNorth China, which has probably expanded the magma channel of the Changbaishanvolcano, increasing the possibility of its eruption.When a large earthquake occurs, the stress and strain fields around the rupturedfault change dramatically, leading to the stress and strain adjustments in surroundingcrust, which include the afterslip on the rupture plane, viscoelastic relaxation in thelower crust and upper mantle, and the tectonic activity changes in neighboring areas,such as volcanoes and active faults. Comparing with the long-term process ofearthquake gestation, the deformation in this period is pretty quick and remarkable.Hence, modeling the post-seismic deformation field allow us to learn its mechanismand study post-seismic stress and strain field evolution, which can help understand theimpact of major earthquakes on tectonic activity and variation of seismic hazards insurrounding areas.Based on the continuous GPS observations of GEONET of Japan and CMONOCof China，this thesis analyzes the post-seismic deformation of the Mw9.0Tohoku-Okiearthquake. The main contents and results of this thesis involve in the following threeaspects:1) Adopt the uniform model and method to process the continuous GPSobservations of Japan and Northeast and North China, obtain the post-seismic positiontime series of these areas. The post-seismic displacement shows the characteristics ofdecay with time clearly, and the amplitude and speed of attenuation are in direct proportion to the distance from the epicenter.2) Based on the post-seismic position time series of Japan, this work archives thepost-seismic displacement decaying time constant and each station’s attenuationamplitude by using a logarithmic function. The obtained time constant is8days thatshows a rapid decaying process in the afterslip. Thus the consistence betweenattenuation amplitude and direction of coseismic displacement illustrates the source ofpost-seismic and coseismic are similar. Modeling the afterslip on the ruptured planewith the constraint of post-seismic displacement attenuation amplitude shows14days’slip on the fault plane after this earthquake is2.4m, and the released seismic momentis4.04×10²¹Nm which is equivalent to a Mw8.4earthquake. It is inferred that themain source of post-seismic deformation of Northeast and North China is probablythe viscoelastic stress relaxation in the lower crust and upper mantle throughcomparing with the surface displacement caused by coseismic dislocation.3) Interpolate the horizontal principal strain distribution’s variation with time byusing the continuous GPS data of Northeast and North China with a slip regressionmethod based on the continuous strain field. From the spatial view, the strain field ofNortheast and North China presents the northwest-southeast extension that weakenedfrom east to west. The maximum strain occurred at the middle of the Dunhua-Mishanfault of the northern Tanlu fault zone with a value40nano-strain (1nano-strain equals1×10^-9, the same below) as the same level with the coseismic until the December in2012. From the time view, the tensile strain caused by post-seismic deformationincreased gradually over time, and then leveled off. The result of surface expansionalso shows Northeast China experienced a significant surface expansion, especially onthe north Tanlu fault zone. Therefore, the seismic activity in the future of the northTanlu fault zone should receive concern.