Core-Reflected Wave May Have Shifted Japan 5-6 Millimeters After 2011 Quake
Updated
Updated · ScienceAlert · Jun 18
Core-Reflected Wave May Have Shifted Japan 5-6 Millimeters After 2011 Quake
3 articles · Updated · ScienceAlert · Jun 18
Summary
GPS data from the 2011 magnitude 9.0 Tohoku earthquake show parts of Japan moved 5 to 6 millimeters eastward just as an ScS wave returned from the core-mantle boundary.
2,900 kilometers below Earth’s surface, that shear wave reflected off the boundary between the mantle and liquid outer core, then reached Japan nearly simultaneously across a broad area.
Modeling suggests the returning pulse triggered millimeter-to-centimeter fault slip along a vast section of the plate boundary rather than a single major rupture, matching the observed surface shift better than alternatives.
The inferred slip released energy comparable to a magnitude 7.5 quake but produced little extra shaking because the motion was spread out, not concentrated in one break.
If confirmed, the Science study would mark the first known fault-slip event triggered by a seismic wave reflected from the core-mantle boundary, pointing to a previously overlooked hazard minutes after major earthquakes.
Could a megaquake's 'echo' from Earth's core trigger disaster minutes after the main shaking stops?
With new delayed threats found, like core-reflected waves and gas releases, what other post-quake dangers are we missing?
Unveiling Japan’s Silent 5mm Shift: Core-Reflected Waves from the 2011 Tohoku Quake and the New Era of Earthquake Hazard Assessment
Overview
Following the 2011 magnitude 9.0 Tohoku earthquake, scientists discovered that about 15 minutes after the main shock, the entire Japanese archipelago shifted uniformly eastward by 5-6 millimeters. This unusual movement was triggered by powerful ScS seismic waves, which originated from the earthquake, traveled deep into the Earth, reflected off the core, and returned to the surface. The intense shaking from the quake weakened Japan’s plate boundaries, making them more susceptible to movement when these core-reflected waves arrived. This finding reveals that mega-quakes can cause widespread, delayed ground shifts, changing how we understand earthquake impacts.