Great earthquakes on the order of magnitude 9 are accompanied by large and broad-scale crustal deformation. Most commonly, uplift occurs immediately atop the source area where fault rupture has occurred, whereas subsidence occurs landward of it. During the great Tohoku earthquake, uplift occurred over broad regions in marine areas, where the source was located, and caused the tsunami. By contrast, broad-scale subsidence took place in coastal areas that lie landward of the source region. However, areas that sank during the earthquake may rise in future.

Similar crustal deformation took place during the 1960 Chile earthquake. In coastal areas located landward of the source region, the ground subsided 1-2 m over broad areas during the earthquake, but this was followed by slow uplift (e.g., Annual Report on Active Fault and Paleoearthquake Researches, No. 4, 265-280). The time that elapsed between the earthquake and the onset of uplift differs from one place to another and remains uncertain. This type of uplift is called post-seismic deformation, and is thought to occur because of slow post-seismic slip that takes place along the deep extension of the plate boundary that broke during the earthquake.

Also, there is no geological evidence for large subsidence taking place during the past 100,000-200,000 years in coastal areas of the Tohoku District. The Jogan earthquake of 869 from the Heian period (8-12c) is thought to have been an event of the same type, and similar earthquakes have occurred repeatedly at intervals of about 500 years. The lack of recognizable long-term subsidence in this region despite this fact strongly suggests that an uplift movement is likely to take place in future to cancel out the subsidence generated by the earthquake. Surveys conducted by AIST on the Sendai Plain also produced data indicating possible uplift of the plain during the Muromachi period (14-16c).

One cannot tell for sure right now whether uplift is going to take place along the Pacific coast of northeastern Japan as it did so in Chile, but one should keep an eye on crustal deformation that will follow.