April 2011 Miyagi earthquake April 2011 Miyagi earthquake The April 2011 Miyagi earthquake (Japanese: ) occurred off the coast of Miyagi Prefecture, approximately east of Sendai, Japan. The thrust earthquake was classified as an aftershock of the March 11 Tōhoku earthquake, and occurred at 23:32 JST (14:32 UTC) on Thursday, 7 April 2011. Several tsunami warnings were issued for the northeastern coast of Honshu; however, they were all canceled 90 minutes later. Over 3 million households in the area were left without power, and several nuclear plants suffered minor inconveniences. There was no major structural damage, but the quake killed at least 4 people
2011 Tōhoku earthquake and tsunami intensities were smaller than the actual ones in some places, especially in Kanto, Koshinetsu, and Northern Tōhoku regions where the populace warning did not trigger. According to the JMA , reasons for the underestimation include a saturated magnitude scale when using maximum amplitude as input, failure to fully take into account the area of the hypocenter, and the initial amplitude of the earthquake being less than that which would be predicted by an empirical relationship. There were also cases where large differences between estimated intensities by the Earthquake Early Warning system and the actual intensities occurred in the aftershocks and