The April 7 quake was the product of thrust faulting along the subduction zone where the Pacific Plate dives beneath the North American Plate -- the same boundary that had unleashed the March 11 megathrust. By April 7, the aftershock sequence from that main event already included over 58 earthquakes of magnitude 6.0 or greater, with two others reaching 7.0. The Japan Meteorological Agency initially estimated this latest tremor at 7.4 before revising it downward to 7.1. Shaking was felt as far south as Tokyo, roughly 333 kilometers from the epicenter. For residents of Sendai and the Miyagi coast, the violent rocking reopened fresh trauma. Tsunami warnings went out immediately for Miyagi Prefecture, with alerts extending to Iwate, Fukushima, Aomori, and Ibaraki Prefectures. Waves of 0.5 to 1 meter were anticipated. Coastal communities that had lost everything a month earlier evacuated once more.

The most widespread impact was the power failure. Some 3.6 million households across several prefectures lost electricity, and by the following day many still sat in the dark. The outage cascaded through critical infrastructure. At the Onagawa Nuclear Power Plant, two of three power lines supplying fuel-rod cooling systems were severed, and radioactive water leaked from spent fuel pools at three of its reactors -- though radiation levels outside the plant boundary did not change. Five coal-fired power plants shut down automatically, compounding energy shortages that were already severe after the March disaster. At the crippled Fukushima Daiichi plant, where engineers were still fighting to prevent a full meltdown, workers evacuated as a precaution. The plant sustained no additional damage, but the evacuation underscored how thin the margins had become.

The earthquake killed four people and injured 141. Among the dead was an elderly woman in Yamagata Prefecture whose medical ventilator failed when the power cut out -- a reminder that modern disasters do not always kill through dramatic force. Falling objects, shattered glass, and collapsed shelving caused injuries ranging from cuts and bruises to bone fractures. Structurally, the region held. Buildings designed to Japanese seismic codes, among the strictest in the world, absorbed the shaking without major collapse. Roads sustained some damage, and a handful of homes were compromised, but the toll was remarkably light for a quake of this magnitude. Japan's investment in earthquake engineering had, once again, saved lives on a scale that is difficult to quantify.

The tsunami warnings were canceled within 90 minutes. The Nikkei stock index dropped sharply at the close of trading but rebounded the following day when the scale of damage proved limited. Life, such as it was in post-disaster Tohoku, resumed. But the psychological toll was harder to measure. For communities already dealing with grief, displacement, and uncertainty about nuclear contamination, the April 7 earthquake was a cruel reminder that the earth beneath them had not finished moving. The aftershock sequence from the March 11 event would continue for years, with significant tremors recorded as late as 2021. The epicenter of the April 7 quake lies beneath the Pacific Ocean roughly 66 kilometers east of Sendai, in waters that appear calm and featureless from the air -- an unremarkable patch of sea that belies the tectonic violence churning below.