1.8 microseconds shorter. Aftershocks Japan experienced over 1,000 aftershocks since the earthquake, with 80 registering over magnitude 6.0 Mw and several of which have been over magnitude 7.0 Mw. A magnitude 7.4 Mw at 15:08 (JST), 7.9 Mw at 15:15 and a 7.7 Mw quake at 15:26 all occurred on 11 March. A month later, a major aftershock struck offshore on 7 April with a magnitude of 7.1 Mw. Its epicenter was underwater, off the coast of Sendai. The Japan Meteorological Agency assigned a magnitude of 7.4 MJMA, while the U.S. Geological Survey lowered it to 7.1 Mw. At least four people were killed, and electricity was cut off across much of northern Japan including the loss of external power to Higashidōri Nuclear Power Plant and Rokkasho Reprocessing Plant. Four days later on 11 April, another magnitude 7.1 Mw aftershock struck Fukushima, causing additional damage and killing a total of three people. On 7 December 2012 a large aftershock of magnitude 7.3 Mw caused a minor tsunami, and again on 26 October 2013 a small tsunami was recorded after a 7.1 Mw aftershock. As of 16 March 2012 aftershocks continued, totaling 1887 events over magnitude 4.0; a regularly updated map showing all shocks of magnitude 4.5 and above near or off the east coast of Honshu in the last seven days showed over 20 events. there had been 869 aftershocks of 5.0 Mw or greater, 118 of 6.0 Mw or greater, and 9 over 7.0 Mw as reported by the Japanese Meteorological Agency. The number of aftershocks was associated with decreased health across Japan. On 13 February 2021, a magnitude 7.1–7.3 earthquake struck off the coast of Sendai. It caused some damage in Miyagi and Fukushima prefectures. One person was killed, and 185 were injured. Land subsidence The Geospatial Information Authority of Japan reported land subsidence based on the height of triangulation stations in the area measured by GPS as compared to their previous values from 14 April 2011. Miyako, Iwate – Yamada, Iwate – Ōtsuchi, Iwate – Kamaishi, Iwate – Ōfunato, Iwate – Rikuzentakata, Iwate – Kesennuma, Miyagi – Minamisanriku, Miyagi – Oshika Peninsula, Miyagi – Ishinomaki, Miyagi – Higashimatsushima, Miyagi – Iwanuma, Miyagi – Sōma, Fukushima – Scientists say that the subsidence is permanent. As a result, the communities in question are now more susceptible to flooding during high tides. Earthquake Warning System One minute before the earthquake