A Seismic Wave from Japan's 2011 Earthquake Triggered a Global Shift A seismic wave generated by Japan's 2011 magnitude-9 Tohoku-Oki earthquake traveled nearly 2,900 kilometers into Earth's core, bounced off the outer core, and returned to the surface 13 minutes later, causing Japan to shift eastward by approximately six millimeters. This phenomenon, the first of its kind ever recorded, was identified by researchers analyzing GPS data from the earthquake, which had been unresolved for over a decade. For 15 years following the 2011 disaster, a small anomaly in GPS data remained unexplained. Approximately 15 minutes after the main shock struck off Japan's northeastern coast, GPS stations across the country registered a step-like eastward displacement of five to six millimeters. The shift was too minor to be felt by people or cause damage, and it did not align with any known aftershocks. Despite being noted in subsequent data compilations, the signal remained uninterpreted until a 2026 study by a team led by Sunyoung Park, an assistant professor at the University of Chicago, provided a groundbreaking explanation. The team concluded that the displacement was caused by an ScS wave—a shear wave that traveled downward from the earthquake's epicenter, reflected off the core-mantle boundary at approximately 2,890 kilometers depth, and returned to the surface as a shear wave. The reflection occurred because shear waves cannot propagate through liquid, and Earth's outer core is composed of molten iron and nickel. The wave's round-trip journey took about 13 minutes, arriving simultaneously across Japan and triggering small additional slip on already-stressed megathrust interfaces along the country's tectonic plate boundaries. The slip event, though minor, released energy equivalent to a magnitude-7.5 earthquake.#japan #university_of_chicago #sunyoung_park #tohoku_earthquake #scs_wave
