the 2011 tōhoku earthquake and tsunami was a 9.0-magnitude earthquake followed by tsunami waves. it was measured at 8.4 on the jma seismic intensity scale the earthquake happened off sendai, miyagi prefecture, on the east coast of the tōhoku of japan, on march 11, 2011 at 05:46:23 utc. it was at a depth of 24.4 km (15.2 miles). it was the most powerful earthquake to hit japan in recorded history. it was also the fourth most powerful earthquake on earth since modern record-keeping began in 1900.