Very dense geophysical measurements both on land
and offshore Japan made this event the best recorded
subduction-zone earthquake in the world.
The nation-wide land-based GPS network with more
than 1000 stations recorded large coseismic movements
with a maximum amount of 5.3 m eastward and 1.2 m
downward. The repeated marine geophysical measurements,
such as GPS/acoustic positioning, bottom
pressure gauge, or multi-beam swath bathymetry survey,
started before the 2011 Tohoku earthquake, detected huge
seafloor displacement, approximately 50 m in horizontal
direction.