2011 northern Nagano earthquake

What Happened

At 3:59 a.m. Japan Standard Time on 12 March 2011, an earthquake struck the northern tip of Nagano Prefecture, close to the border with Niigata Prefecture. The hypocenter lay at a depth of 8 km, and the earthquake registered a magnitude of 6.7 on the Japan Meteorological Agency's scale (MJMA). The shaking was strongest in the village of Sakae in northern Nagano, where the JMA seismic intensity scale reached shindo 6+ (震度6強, shindo roku-kyō), the second-highest level on that scale.

Damage was concentrated in and around Sakae, and three people were killed. Because the village absorbed the worst of the impact, the event is also remembered as the Sakae earthquake (栄村大震災, Sakae-mura Daishinsai).

The timing was brutal. The earthquake struck less than eighteen hours after the Tōhoku earthquake of 11 March 2011, the magnitude 9.0 event off the Pacific coast of northern Honshu that triggered the tsunami and the Fukushima nuclear disaster. Northern Nagano is roughly 250 km southwest of the Tōhoku epicentre, and the 12 March shock was a separate rupture on a separate fault system, not an aftershock of the larger event.

Background

Japan sits on the boundary of four tectonic plates, and the Japanese archipelago experiences a substantial share of the world's large earthquakes. The northern Nagano–Niigata border region lies in a zone of active crustal faulting, where the deformation of the islands under compressional stress produces shallow, inland earthquakes rather than the deep offshore megathrust events that generate tsunamis.

The 2011 northern Nagano earthquake was a shallow inland event of exactly this type. Its hypocenter at 8 km depth placed it within the brittle upper crust, which is why a magnitude 6.7 earthquake produced such intense local shaking. Shallow ruptures concentrate their energy near the surface: the same magnitude at greater depth would have been felt over a wider area but with less violence at any one point.

The date fell in the 23rd year of the Heisei era (平成23年, Heisei nijūsan-nen), the period of Emperor Akihito's reign running from 1989 to 2019. The earthquake's coordinates, 36.985°N, 138.597°E, place it in the mountainous interior of central Honshu, a region of heavy snowfall, steep terrain and scattered rural settlements.

Why It Mattered

The earthquake's historical weight comes largely from its timing. It arrived on the morning after the Tōhoku earthquake, at a moment when the entire country's attention, emergency response capacity and news coverage were fixed on the catastrophe unfolding along the Pacific coast. A destructive inland earthquake in a sparsely populated mountain village competed for attention with a disaster of vastly greater scale.

For Sakae and the surrounding communities, the consequences were immediate and physical. The shindo 6+ shaking damaged houses, roads and slopes, and the three deaths made the event lethal in its own right. In a village of small settlements and older wooden housing, intense shallow shaking is especially dangerous, and the winter conditions of early March in the mountains of northern Nagano added further hardship for residents and responders.

The earthquake also illustrates a recurring problem in Japanese disaster history: the compounding of disasters. A major event can consume the resources and attention that a second, simultaneous event requires. Communities in northern Nagano had to manage their own emergency response while the national apparatus was mobilised for a disaster hundreds of kilometres away.

The Name in Japanese

The Japanese name of the earthquake is 長野県北部地震. Its kana reading is ながのけんほくぶじしん, and its romaji is Nagano-ken Hokubu Jishin. The name is a straightforward descriptive compound: it states the prefecture, the part of it affected, and the type of event.

Breaking it down character by character:

長 — read naga here. Meaning: long. It is the first element of the place name Nagano.

野 — read no here. Meaning: field, plain, open country. Together, 長野 (Nagano) means "long field" and is the name of both the prefecture and its capital city.

県 — read ken. Meaning: prefecture. Japan's 47 top-level administrative divisions are called 都道府県 (todōfuken), and 県 is the term used for most of them, including Nagano.

北 — read hoku. Meaning: north. It specifies that the earthquake occurred in the northern part of the prefecture, not the whole of it.

部 — read bu. Meaning: part, section, portion. Combined with 北, the compound 北部 (hokubu) means "northern part".

地 — read ji. Meaning: ground, earth, land.

震 — read shin. Meaning: shake, quake, tremor. Combined, 地震 (jishin) is the standard Japanese word for "earthquake".

Read as a whole, the name parses as Nagano (長野) + prefecture (県) + northern part (北部) + earthquake (地震): "the northern Nagano Prefecture earthquake". The alternative name, 栄村大震災 (Sakae-mura Daishinsai), uses 栄 (Sakae, the village name, meaning "flourishing" or "prosperity"), 村 (mura, village), 大 (dai, great), and 震災 (shinsai, earthquake disaster). The word 震災 is reserved in Japanese usage for earthquakes that cause serious damage, which is why it appears in the name given to the event by the community that suffered it.

Key Figures

• Date: 12 March 2011
• Time: 3:59 JST
• Magnitude: MJMA 6.7
• Hypocenter depth: 8 km
• Coordinates: 36.985°N, 138.597°E
• Maximum intensity: shindo 6+ (震度6強), recorded in Sakae, Nagano
• Deaths: 3
• Era: Heisei 23 (平成23年), within the Heisei period of 1989–2019
• Location: northern Nagano Prefecture, near the border with Niigata Prefecture