A powerful offshore earthquake struck the Eastern coast of Honshu, Japan, late this afternoon, triggering a coastal alert for potential tsunami activity. The seismic event, initially assessed at magnitude 6.5, was later revised to magnitude 6.7 by the Japan Meteorological Agency (JMA). Occurring at approximately 5:03 p.m. local time, the quake had a very shallow hypocenter of about 10 kilometers, magnifying its impact across the northeastern regions.
The JMA immediately issued a tsunami advisory specifically for Iwate Prefecture. This alert suggests a risk of sea level changes, with waves potentially reaching up to one meter high. Authorities moved swiftly to warn residents and visitors in vulnerable coastal areas, urging immediate evacuation from shorelines and river estuaries. The advisory stressed that people must not approach the coast to observe the incoming waves and should halt all water and coastal activities immediately.
Shaking Intensity and Affected Regions
The epicenter was situated off the coast of Iwate Prefecture, though significant shaking was felt across multiple prefectures in the Tohoku region. The maximum intensity recorded was Grade 4 on Japan’s seven-point shindo scale of seismic intensity. This level of shaking indicates a moderate tremor where objects may rattle strongly, and some people might become frightened.
Areas reporting the maximum intensity of Grade 4 included Morioka City and Yahaba Town in Iwate, as well as Wakuya Town in neighboring Miyagi Prefecture.
A broader area also experienced Grade 3 shaking, which is sufficient to be felt distinctly indoors. These areas stretched across several prefectures and included:
- Iwate: Ninohe and Hachimantai
- Miyagi: Tome and Kurihara
- Aomori: Aomori City and Hachinohe
- Akita: Katagami
- Yamagata: Tsuruoka
Understanding Tsunami Risks
The JMA emphasized the critical nature of the tsunami advisory. Unlike a warning, where larger waves are expected, an advisory indicates imminent danger from smaller waves and strong currents. Even waves under one meter can be extremely dangerous. The agency highlighted that tsunami waves rarely arrive as a single surge; they often arrive in multiple waves, with subsequent surges potentially increasing suddenly in height.
Coastal residents and visitors must understand that even seemingly minor fluctuations in sea level after an earthquake can conceal powerful, unpredictable currents capable of sweeping away people and heavy debris.
Safety Recommendations
For those currently in or near the advisory area, adherence to official guidance is mandatory:
- Move Inland: Immediately vacate coastlines, beaches, and river mouths for higher ground.
- Stay Informed: Follow local disaster updates via radio, television, and official channels.
- Do Not Explore: Never go near the water to “see” the tsunami; the danger is invisible and sudden.
This incident underscores Japan’s constant vulnerability to seismic events and the effectiveness of its rapid early warning system. While the immediate risk assessment suggests manageable wave heights, the event serves as a crucial reminder for residents to maintain vigilance regarding essential earthquake and tsunami preparedness protocols. Authorities will continue to monitor the situation for potential aftershocks or changes in sea activity.