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7h ago

Core‑Reflected Seismic Wave Pushed Japan East After 2011 Quake

Researchers conclude a shear wave that plunged to Earth’s core and returned minutes after the Mw 9.0 Tōhoku shock likely triggered synchronized, small slips across plate boundaries and is prompting calls for more observation and modeling.

Damage from Japan's 2011 earthquake and tsunami. Scientists found the quake's waves traveled to Earth's core and back.
A house partially collapsed and tilted sharply onto its side amid scattered debris and other damaged buildings.

Overview

  • Researchers reanalyzed Japan’s dense GNSS and seismic records and found a near‑simultaneous 5–6 millimeter eastward step across almost the entire country that occurred about 13–16 minutes after the March 11, 2011 Tōhoku earthquake.
  • The team identified a returning core‑reflected shear wave (ScS) that arrived at that time and used forward models to show the pulse could have nudged low‑amplitude slip on multiple plate interfaces across roughly 3,000 kilometers.
  • Modeling estimates the distributed slip released total energy comparable to about a magnitude 7.5 event while producing only millimeter‑to‑centimeter surface offsets and little extra shaking, which helps explain why it went unnoticed by people.
  • The authors tested and rejected common alternatives such as GNSS processing glitches, a submarine landslide, or prolonged mainshock rupture and describe this as the first documented case of a core‑reflected wave triggering surface fault slip.
  • Scientists say the result, published June 18, 2026 in Science, highlights a previously unrecognized mode of delayed triggering and underlines the need for denser offshore GNSS, targeted modeling, and reexamination of post‑quake hazard windows.