M6.4 Earthquake Off Sanriku Coast Shakes Tohoku, Tsunami Advisory Issued

Around 5:03 PM on November 9, 2025, an earthquake with a magnitude of 6.4 (some reports indicate 6.7) occurred off the coast of Sanriku, causing strong shaking primarily across the Tohoku region. According to the Japan Meteorological Agency (JMA), a maximum seismic intensity of 4 was recorded in northern and southern Iwate Prefecture, and northern and central Miyagi Prefecture. Following the earthquake, a tsunami advisory was issued for the coastal areas of Iwate Prefecture, urging residents in those regions to exercise extreme caution.

Immediately after the quake, Emergency Earthquake Warnings (EEW) blared across a wide area. On X (formerly Twitter), numerous posts expressed surprise and fear, with comments like "My heart was pounding like crazy" and "Emergency Earthquake Warnings are terrifying." Some users voiced heightened anxiety due to a series of earthquakes since that morning, saying, "The continuous earthquakes since this morning are unsettling," and "The EEW went off after a long shake just now, so I was scared and immediately turned off the heater." Many also described the psychological toll of repeated tremors: "Constantly shaking feels like it's messing with my vestibular system," and "Frequent small earthquakes are draining my energy."

Users also shared their immediate reactions and reflections during the EEW, such as "I opened the doors and windows, but perhaps what I should have done was evacuate to the living room." There were also accounts from individuals whose hearing-impaired family members did not notice the shaking, causing panic, and a unique post about a pet degu repeatedly making alarm calls like a "live Emergency Earthquake Warning🚨."

Regarding information dissemination, the Prime Minister's Office Disaster and Crisis Management Information account promptly shared earthquake information and tsunami advisories on X, garnering gratitude from users who appreciated the "immediate sharing of information." However, some dissatisfaction arose when NHK's sumo broadcast was interrupted by the EEW, with comments like "They should at least broadcast sumo," leading to various discussions about the optimal way to transmit information. Voices were also heard suggesting that video streaming services like AbemaTV were useful for emergency broadcasts, not just traditional television.

The earthquake also impacted transportation, with reports of delays on the Tohoku Shinkansen. While no major damage has been confirmed so far, concerns were raised about the Fukushima Daiichi Nuclear Power Plant, with questions like "Is Fukuitchi okay?" The possibility of continued aftershocks also spread anxiety, with comments such as "It'll be scary if aftershocks continue during the night."

The Japan Meteorological Agency continues to maintain the tsunami advisory, urging residents to prioritize their personal safety. Particular caution is advised for coastal residents, who should stay attentive to future updates and take steps to ensure their safety.

The context

Japan is one of the most seismically active countries in the world, situated along the Pacific Ring of Fire where several major tectonic plates meet. Earthquakes are a frequent occurrence, leading to advanced warning systems and strict building codes.

The **Sanriku Coast**, located in the northeastern Tohoku region of Honshu island, is particularly prone to large earthquakes and tsunamis dueastic to its proximity to the Japan Trench, where the Pacific Plate subducts beneath the Okhotsk Plate (part of the North American Plate). This area was the epicenter of the devastating 2011 Great East Japan Earthquake and Tsunami.

The **Tohoku Region** is the northeastern part of Japan's main island of Honshu. It's a geographically diverse area known for its natural beauty, but also its vulnerability to natural disasters.

The **Japan Meteorological Agency (JMA) Seismic Intensity Scale (Shindo)** measures the intensity of shaking at a specific location, rather than the total energy of the earthquake (magnitude). Shindo levels range from 0 to 7. A Shindo 4, as experienced in this earthquake, means that most people feel the shaking, and objects hanging may swing considerably. Unstable objects may fall.

The **Emergency Earthquake Warning (EEW)** system is an advanced public alert system in Japan designed to provide a few seconds to tens of seconds of warning before strong seismic waves (S-waves) arrive at a location. It's triggered by the detection of faster, but less destructive, P-waves.

A **Tsunami Advisory (Tsunami Chuiho)** is the lowest level of tsunami warning issued by the JMA. It indicates that a tsunami of up to 1 meter is expected, and advises people to evacuate coastal areas and stay away from the sea. It is less severe than a Tsunami Warning (Tsunami Keihō), which anticipates larger tsunamis.

Concerns about the **Fukushima Daiichi Nuclear Power Plant** are common during significant earthquakes in Japan. The plant suffered a meltdown during the 2011 earthquake and tsunami. Although it has been stabilized and decommissioning efforts are underway, any seismic activity in the region naturally raises public concern about its status and potential for further issues.