2011 Shizuoka earthquake

What Happened

At 22:31 Japan Standard Time on 15 March 2011, an earthquake struck Shizuoka Prefecture in central Honshu. Its epicentre lay roughly 42 km (26 mi) north-northeast of Shizuoka City, at coordinates 35.31°N, 138.71°E. The shaking lasted only seconds, but it was strong enough to injure 80 people and knock out power across parts of the prefecture.

The earthquake registered a moment magnitude (Mw) of 6.0, or 6.4 on the Japan Meteorological Agency's own magnitude scale (MJMA). Its focus was shallow — about 9 km (5.6 mi) below the surface — which is why a moderate quake produced such sharp local shaking. The JMA's intensity scale, called shindo (震度), runs from 0 to 7; this event reached shindo 6+ at Fujinomiya, a city at the southern foot of Mount Fuji. On the Modified Mercalli Intensity scale, that corresponds to VIII, or "Severe."

Seismologists classified the rupture as a sinistral strike-slip fault earthquake — meaning the two blocks of rock on either side of the fault slid horizontally past one another, with the far side moving to the left when viewed from across the fault line. No tsunami followed.

Background

The earthquake occurred four days after the Tōhoku earthquake of 11 March 2011, the magnitude 9.0 megathrust event off the coast of northeastern Japan that triggered the tsunami and the Fukushima Daiichi nuclear disaster. In the days between the two events, seismic stations across eastern and central Honshu recorded a surge of smaller quakes. The Shizuoka event is thought to have been one of them — a triggered earthquake, set off when the massive Tōhoku rupture redistributed stress through the crust hundreds of kilometres to the south.

The location was significant. The hypocenter is believed to lie near the presumed site of the magma chamber beneath Mount Fuji, Japan's highest peak and an active volcano. Fuji sits at the junction of three tectonic plates — the Philippine Sea Plate, the Eurasian Plate, and the North American Plate — a triple boundary that generates frequent seismic activity. Low-frequency tremors had been recorded under Fuji before, and the 2011 event drew fresh attention from volcanologists watching for any change in the mountain's behaviour.

The quake fell in the 23rd year of the Heisei era (平成), the reign period of Emperor Akihito that ran from 1989 to 2019. Coming in the same week as Tōhoku, it was initially overshadowed in the national news, but its proximity to Fuji gave it outsized importance in later scientific study.

Why It Mattered

The 2011 Shizuoka earthquake mattered less for its own damage than for what it revealed about how large earthquakes interact. The Tōhoku event was one of the most powerful ever recorded, and its effects rippled through the crust far beyond its own rupture zone. The Shizuoka quake, four days later and roughly 400 km away, became a textbook case of a triggered event — evidence that a megathrust earthquake can push distant faults closer to failure.

Its position near Mount Fuji made it a focus of volcanic monitoring. Any seismic activity in the Fuji region is watched closely, because the mountain last erupted in 1707, in what is called the Hōei eruption, and remains classified as an active volcano. The 2011 quake did not trigger an eruption, but it added data to models of the magma system beneath the peak.

The event also tested Japan's earthquake early warning system, which had been operating nationally since 2007. Coming days after Tōhoku had saturated emergency services, the Shizuoka quake showed how the system performed under sustained strain. The 80 injuries were mostly minor — falls, cuts from broken glass, and similar — and the power outages were restored within hours. Compared with the catastrophe unfolding to the north, the toll was small, but the quake served as a reminder that the Tōhoku rupture had unsettled faults across the whole of eastern Japan.

The Name in Japanese

The Japanese name of this earthquake is 静岡県東部地震, read in kana as しずおかけんとうぶじしん and romanised as Shizuoka-ken Tōbu Jishin. The name is a compound of place and event, built the way Japanese usually names earthquakes: the location first, then the word for earthquake.

Breaking it down character by character:

• 静 (read しず, shizu) — "quiet" or "calm."
• 岡 (read おか, oka) — "hill" or "ridge."
• 県 (read けん, ken) — "prefecture," the administrative unit used for Japan's 47 top-level divisions.
• 東 (read とう, tō) — "east."
• 部 (read ぶ, bu) — "part" or "section." Together, 東部 (tōbu) means "the eastern part."
• 地 (read じ, ji) — "ground" or "earth."
• 震 (read しん, shin) — "shake" or "quake." Together, 地震 (jishin) means "earthquake."

So the full name translates literally as "Shizuoka Prefecture Eastern-Part Earthquake." The first two characters, 静岡, form the prefecture's name; the reading Shizuoka is a place name and does not carry its literal meaning of "quiet hill" in everyday use. Note that 東部 (tōbu) uses the kanji 東, the same character found in 東京 (Tōkyō, "eastern capital") and in 東北 (Tōhoku, "northeast") — the region devastated four days earlier. Readers who know the word Tōhoku will recognise the same 東 element here, meaning "east."

The kana reading しずおかけんとうぶじしん is written without spaces, as is standard in Japanese. When romanised with word boundaries, it becomes Shizuoka-ken Tōbu Jishin. The macron over the ō in Tōbu marks a long vowel; without it, the word would be misread.

Key Figures

• Date and time: 15 March 2011, 22:31 JST.
• Epicentre: 35.31°N, 138.71°E — approximately 42 km (26 mi) north-northeast of Shizuoka City.
• Depth: 9 km (5.6 mi).
• Magnitude: Mw 6.0; MJMA 6.4.
• Maximum intensity: Shindo 6+ (Fujinomiya); VIII (Severe) on the Modified Mercalli scale.
• Fault type: Sinistral strike-slip.
• Injuries: 80.
• Other effects: Power outages.
• Era: Heisei 23 (平成23年), the 23rd year of the Heisei era.