A Japan earthquake of magnitude 5.5 struck southern Ibaraki Prefecture at 7:46 p.m. on Tuesday. It measured lower 5 on Japan's seismic intensity scale and had no threat of a tsunami.
The quake hit at a depth of 50 kilometers. People in Ota and the town of Chiyoda in Gunma Prefecture felt lower 5 shaking, and so did people in Kazo and Honjo and the town of Misato in Saitama Prefecture.
Level 4 shaking and under was recorded across a wide area, including parts of eastern Japan, western Japan, central Japan and north-eastern Japan. That spread matters to people far beyond southern Ibaraki Prefecture, because the shaking did not stay confined to one locality.
Japan seismic intensity scale
Japan uses a seismic intensity scale that measures how strongly shaking is felt at the surface. This quake's lower 5 reading placed it among the stronger levels reported for local shaking, even though its magnitude was 5.5 and its depth was 50 kilometers.
The difference between magnitude and intensity explains why people in several places reported shaking while the event remained offshore in effect and did not carry a tsunami threat. The quake's reach was broad enough to be noticed in multiple regions, but the source gave no further developments beyond the shaking itself.
Ota and the surrounding area
People in Ota and the town of Chiyoda in Gunma Prefecture were among those who felt lower 5 shaking. The same level was felt in Kazo and Honjo and the town of Misato in Saitama Prefecture, making the evening quake a shared event across a wide stretch of Japan.
For readers in those places, the immediate practical point is simple: the reported shaking passed through several communities at once, but no tsunami warning followed. The report leaves the next question centered on impact on the ground in those places, including whether any damage or injuries emerged after the shaking stopped.
