A newly identified seismic event likely shifted Japan for good

Key Points:

• A new study led by University of Chicago geophysicist Sunyoung Park discovered that about 15 minutes after the 9.0 magnitude 2011 Japan earthquake, the entire country shifted eastward by 5 to 6 millimeters, marking the broadest permanent ground movement ever recorded.
• This shift was caused by seismic waves from the earthquake traveling down to Earth's core and rebounding to the crust, displacing four major tectonic plates simultaneously across approximately 1,800 miles, a previously undocumented seismic phenomenon.
• Unlike typical aftershocks, this wave-induced movement occurred uniformly and could potentially be anticipated due to the known 15-minute round-trip travel time of seismic waves to the core and back, although the energy was dispersed over a large area, causing less intense shaking.
• The event released energy comparable to a magnitude 7.5 earthquake but was less damaging because of its broad distribution; it highlights a new seismic hazard that policymakers should consider in earthquake preparedness.
• Experts note that such deep-core seismic wave effects might occur globally but remain undetected in regions lacking dense seismic and GPS monitoring, emphasizing the need for improved understanding of fault dynamics and earthquake impacts.