How the Earth's mass is redistributed after an earthquake

The information presented below were all obtained from various internet sources (all of which are listed below) and this post is a compilation and a summary, in simple words for ease of understanding of the readers, of the whole process taken into consideration for the research.) Nothing has been directly pasted from a single source. 


The Earth is spherical shaped and count a number of layers. The internal structure of the Earth is as shown

http://www.uwsp.edu/geo/faculty/ritter/glossary/a_d/crust.html

Each layer has specific properties as temperature and pressure (increasing as we go to the core of the earth). When we talk about moving plates so tectonic of plates, the concerned layer is the Lithosphere made of the Mantle plus the Oceanic and Continental crusts; one thing to be known this plate are heavy. There all types of movements occur, as the convergent and divergent boundaries between plates.

The Japanese Earthquake happened at a subduction zone what is basically a type of convergent boundaries between two tectonic plates. These plates can both be Oceanic ones or one of them is Continental. One of the plates, always an Oceanic plate goes under the other ones due to many factors as the temperature, the pressure and the weight, because the Oceanic crust is really heavy compared to Continental crust. As a result, the Oceanic crust is destroyed. As mentioned in the previous articles it moves 3.5 inches annually and at the divergent boundaries are produced basalt for a renewal of the Plates.
(Source: http://news.nationalgeographic.com/news/2010/03/100302-chile-earthquake-earth-axis-shortened-day/)

http://csmres.jmu.edu/geollab/fichter/PlateTect/igevol.html

What happens during a subduction zone earthquake is that the plate that is going down, after a certain time is stuck and as a result the Oceanic plate goes up instead of down. For it to go back again, energy is release and lift up the Continental plate. This energy is released in a small amount of time and that causes an earthquake and after a tsunami. But it also moves the plates, as a result and knowing that the plates are heavy, the Earth’s mass distribution has changed. The following link is an animation of an earthquake in a subduction zone 
(Source: http://news.nationalgeographic.com/news/2010/03/100302-chile-earthquake-earth-axis-shortened-day/)
  Animation Sourse: http://www.jclahr.com/science/earth_science/animate/ .