Story perspectives

Shear Wave Shifts Japan 5 mm After Tohoku, Reveals Hazard

6/19/2026

Summary

Story summary

A shear wave nudged the Japanese archipelago eastward five millimetres minutes after the March 11, 2011 magnitude-9 Tohoku quake, a shift verified by Sunyoung Park of the University of Chicago.
The wave traveled 2,900 kilometres to the boundary and back, generating a ScS signal, an offset of 3,000 kilometres, and magnitude 7.5-equivalent energy.
Scientists say the finding reveals an unknown seismic hazard and recommend monitoring for delayed fault motions after earthquakes.

History

Historical Context

On April 18, 1906 a magnitude-7.9 quake ruptured the San Andreas Fault, killing over 3,000 people, leaving up to 300,000 homeless and destroying more than 80 % of San Francisco. The United States Geological Survey began systematic seismology research, and Andrew Lawson’s 1908 report mapped the fault. The disaster redirected growth toward Los Angeles and spurred today’s worldwide fault-motion monitoring.

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Story summary

A shear wave nudged the Japanese archipelago eastward five millimetres minutes after the March 11, 2011 magnitude-9 Tohoku quake, a shift verified by Sunyoung Park of the University of Chicago.
The wave traveled 2,900 kilometres to the boundary and back, generating a ScS signal, an offset of 3,000 kilometres, and magnitude 7.5-equivalent energy.
Scientists say the finding reveals an unknown seismic hazard and recommend monitoring for delayed fault motions after earthquakes.

1 / 2