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On March 11, 2011, at 05:46:23 UTC, a megaearthquake (magnitude 9.0) occurred near the NE coast of Honshu Island (Japan), which originated near the subduction plate boundary between the Pacific and North American plates. The epicenter has been located at about 130 km east of Sendai City at a depth of about 32 km. A foreshock sequence took place days preceding the mainshock with magnitude 7.3 in March 9. The earthquake has been followed by a devastating tsunami. The location, the geometric parameters, and the focal mechanism are in agreement with the occurrence of the earthquake along the subduction plate boundary. The focal region from seismological analysis indicated that an area of about 500 km × 200 km moved with a maximum displacement of about 24 m near the hypocenter. The Earth Observation Community has made a strong effort to investigate the surface effects by exploiting the satellite data and the geodetic GPS measurements available. The Group on Earth Observation Geohazard Supersites established the Tohoku-Oki Event Supersite. This initiative provided a huge amount of satellite data to the scientific community. The main outcomes concern the measurement of the surface displacement pattern, the detection of surface changes due to damage, and the investigation of coastal changes due to inundation.