A potent magnitude 6.6 Mw intraplate aftershock occurred at 17:16 JST (08:16 UTC) on 11 April, in the Hamadōri region of Fukushima, Japan.

The strong ground movements triggered the reactivation of a nearby geological fault, prompting researchers to conduct extensive surveys in the region.

[1] To the east of the epicentre, the oceanic Pacific plate is subducted beneath the continental Okhotsk microplate, on which much of Honshu's Tōhoku region is situated.

Building stress near the resultant plate boundary has led to the development of shallow inland faults through crustal deformation and folding along the east coast of Tōhoku.

[23] Authorities at Tokyo International Airport closed all runways momentarily,[24] while NTT DoCoMo restricted voice calls in 14 prefectures following the quake.

East Japan Railway Company temporarily suspended its services to restart four of five bullet-train lines; other Shinkansen bullet trains in the region were also halted.

[19] At the risk of a tsunami – which reach their destructive wave heights near shallow coastal waters[30] – local fishing boats along coastlines were shown heading out to sea on national news broadcasts.

[14][31] In response to the earthquake, the fire department dispatched search and rescue teams and emergency crews for relief efforts and damage assessments throughout the affected area.

[27] Former Prime Minister Naoto Kan postponed a press conference scheduled for 17:50 JST marking the one-month anniversary of the catastrophic Tōhoku earthquake and tsunami.

[32] Ever since the earthquake triggered their reactivation, the Shionohira and Yunodake faults have provided essential data for local geological surveys on regional land deformation, sedimentary rock distribution and landslide vulnerability.

[5][7][33] In the earthquake's aftermath, Professor Yagi Hiroshi from the Faculty of Education, Art and Science noted that "a possibility exists for widespread aftershocks of the same size to occur in the near future.