Japan's 2011 Quake Sent Tremors Through Earth's Core, Shifting Island

WHO:

Phys.org - Japan's GPS stations were involved in measuring the seismic activity.

ScienceAlert - A team led by seismologist Sunyoung Park from the University of Chicago conducted the analysis.

WHAT:

Phys.org - A magnitude 9.0 earthquake struck Japan in 2011, causing significant seismic activity.

ScienceAlert - GPS observations indicated that parts of Japan shifted eastward by up to 5 to 6 millimeters.

ScienceAlert - The returning seismic wave is estimated to have released energy equivalent to a magnitude 7.5 earthquake.

ScienceAlert - The findings suggest a previously unrecognized source of seismic hazard from potential reactivation of the mainshock area.

WHERE:

Phys.org - The earthquake occurred off the coast of Japan.

ScienceAlert - The GPS stations involved were part of Japan's GNSS Earth Observation Network System (GEONET).

WHEN:

Phys.org - The earthquake occurred in 2011.

ScienceAlert - The analysis of the seismic data was published in the journal Science.

WHY:

ScienceAlert - The returning shear wave may have triggered a broad pulse of fault slip at the interface between tectonic plates.

HOW:

ScienceAlert - The seismic wave traveled 2,900 kilometers (1,800 miles) down to the core-mantle boundary and was reflected back to the surface.

ScienceAlert - Researchers modeled the returning wave's effects to identify the process that could reproduce the observed signal.

(UPDATED June 19, 2026 14:15 UTC)

A team led by seismologist Sunyoung Park from the University of Chicago has conducted an analysis of seismic activity related to the magnitude 9.0 earthquake that struck off the coast of Japan in 2011, utilizing data from Japan's GNSS Earth Observation Network System. Their findings revealed that parts of Japan shifted eastward by up to 5 to 6 millimeters and suggested a previously unrecognized source of seismic hazard due to the potential reactivation of the mainshock area. The study, published in the journal Science, indicates that the returning seismic wave released energy equivalent to a magnitude 7.5 earthquake, possibly triggering a broad pulse of fault slip at the interface between tectonic plates.