An exciting series of lectures given at the last AGU meeting on the Tohoku earthquake explain a great deal about the tectonic plate interactions that led to the quake along with measuring its magnitude and studying its behaviour which was unusual compared to past large earthquakes. The Tohoku earthquake was a multi-segment earthquake and while earthquakes occur frequently in this region of Japan, the thrust of this earthquake was entirely unexpected and was characterised by a number of large slips.
There is also a history lesson here. The tectonic environment of the Tohoku quake was similar to the mysterious, historic 1907 Sumatra Earthquake (7.6 mag). Although it is difficult to say what happened exactly based on seismograms that were left, the 1907 Sumatra Earthquake may also have been a megathrust event like Tohoku.
All of the AGU Union Lectures, including the ones below, are available on AGU’s Vimeo webpage: http://vimeo.com/user6966590