1984 Nagano earthquake

What Happened

On 14 September 1984 at 08:48 local time, an earthquake struck the western part of Nagano Prefecture in central Japan. The epicentre lay at coordinates 35.79°N, 137.49°E. The shaking registered a surface-wave magnitude of 6.3.

The village of Otaki (王滝, Ōtaki) was destroyed. The earthquake also triggered major landslides across the mountainous terrain of the western prefecture. At least 29 people were killed or left missing, making this the deadliest earthquake to strike anywhere in the world during 1984.

Background

The earthquake occurred during the Shōwa period (昭和, Shōwa, 1926–1989), the reign of Emperor Hirohito. In the Japanese era calendar, the year 1984 corresponds to Shōwa 59 — the fifty-ninth year of Hirohito's reign. Japan in 1984 was in the middle of an economic boom, and the country's infrastructure and emergency-response systems were among the most developed in the world. Even so, a magnitude 6.3 event in a sparsely populated mountain region could still cause catastrophic local damage.

Nagano Prefecture sits in the Chūbu region of Honshū, Japan's main island. The western part of the prefecture, where the earthquake struck, is dominated by steep mountain valleys and volcanic terrain. Otaki, the village most severely affected, is a small mountain community in this western zone. The combination of steep slopes, loose volcanic soil, and heavy rainfall typical of the region makes the area prone to landslides when the ground shakes.

The earthquake struck at 08:48 in the morning, when many residents were at home or beginning their day. The timing contributed to the human toll, as people were inside buildings when they collapsed and when landslides swept down the slopes.

Why It Mattered

The 1984 Nagano earthquake was the deadliest earthquake in the world that year. Its death toll of at least 29 dead or missing was not the result of a single catastrophic collapse but of the combination of ground shaking and the landslides it set off. In mountainous terrain, an earthquake of moderate magnitude can be far more destructive than the same magnitude on flat ground, because the shaking destabilises slopes over a wide area.

The destruction of Otaki village demonstrated how vulnerable isolated mountain communities can be. Rescue and relief operations in such terrain are difficult: roads are blocked by landslides, and access to affected areas can take days. The event reinforced awareness in Japan that earthquake preparedness must account not only for building collapse in cities but also for landslide risk in rural mountain regions.

The earthquake also contributed to the broader Japanese effort to understand and prepare for seismic hazards. Japan sits at the junction of four tectonic plates, and earthquakes are a constant feature of life there. Each significant event adds to the geological record that scientists use to assess future risk. The 1984 Nagano earthquake, with its well-documented landslides, became a reference point for the study of earthquake-triggered slope failures.

The Name in Japanese

The Japanese name of this earthquake is 長野県西部地震.

Kana reading: ながのけんせいぶじしん

Romaji: Nagano-ken Seibu Jishin

The name breaks down into five elements:

長 (read as なが, naga) — "long." This is the first character of 長野 (Nagano), the prefecture name.

野 (read as の, no) — "field" or "plain." Together, 長野 means "long field," and it is the name of both the prefecture and its capital city.

県 (read as けん, ken) — "prefecture." Japan is divided into 47 prefectures, and 県 is the suffix used for most of them. So 長野県 means "Nagano Prefecture."

西 (read as せい, sei) — "west." This character indicates the western part of the prefecture, distinguishing this earthquake from others that might strike elsewhere in Nagano.

部 (read as ぶ, bu) — "part" or "section." Combined with 西, the compound 西部 (せいぶ, seibu) means "western part."

地震 (read as じしん, jishin) — "earthquake." The character 地 (ち, chi) means "ground" or "earth," and 震 (しん, shin) means "shake" or "tremor." Together they form the standard Japanese word for earthquake.

So the full name, 長野県西部地震, translates literally as "Nagano Prefecture Western-Part Earthquake." Japanese earthquake names typically follow this pattern: the place name, followed by a directional or descriptive element, followed by 地震. This makes the names immediately informative to Japanese speakers — the name itself tells you where the earthquake happened.

Note that the reading of 西 changes depending on context. Alone, it is often read にし (nishi). In the compound 西部, it takes the Sino-Japanese reading せい (sei). Similarly, 長 is read なが (naga) in the place name Nagano, but has other readings such as ちょう (chō) in different compounds. This flexibility of kanji readings is one of the central challenges of learning Japanese.

Key Figures

• Date: 14 September 1984 (local time)
• Local time: 08:48
• Magnitude: Ms 6.3
• Epicentre coordinates: 35.79°N, 137.49°E
• Location: Western Nagano Prefecture, Japan
• Village destroyed: Otaki (王滝, Ōtaki)
• Dead or missing: at least 29
• Japanese era: Shōwa 59 (1984), during the Shōwa period (1926–1989)
• Japanese name: 長野県西部地震 (ながのけんせいぶじしん, Nagano-ken Seibu Jishin)