2005 Fukuoka earthquake

What Happened

At 10:53:41 on the morning of 20 March 2005, a magnitude 7.0 earthquake ruptured beneath the Genkai Sea, roughly 40 kilometres northwest of Fukuoka City on the island of Kyushu. The shaking lasted about 30 seconds. The epicentre lay at coordinates 33.7383°N, 130.1750°E, in the strait between Kyushu and the Korean peninsula.

It was the strongest earthquake ever recorded in Fukuoka Prefecture. The Japan Meteorological Agency measured it at MJMA 7.0 — a scale that differs slightly from the moment magnitude used internationally, but which in this case also registered 7.0.

One person died: an elderly woman. More than 1,200 people were injured. The damage was concentrated overwhelmingly in Fukuoka Prefecture, particularly on Genkai Island (玄海島, Genkai-jima), a small island of roughly 700 residents lying close to the epicentre, where nearly 80% of homes were heavily damaged or destroyed. Fukuoka City also suffered significant damage. In total, 20,300 houses were damaged or destroyed. Shaking and structural damage extended into Saga, Nagasaki, Ōita and Yamaguchi Prefectures.

Background

Northern Kyushu had long been considered seismically quiet by Japanese standards. The region sits far from the major subduction zones that generate the great earthquakes of the Pacific coast, and its historical record contains no comparable event. That assumption shaped construction standards, emergency planning and public expectation across Fukuoka Prefecture.

The earthquake of 20 March 2005 struck along a previously unmapped offshore fault in the Genkai Sea (玄海灘, Genkai-nada). Because the fault lay under water and had no recorded history of movement, it appeared on no hazard map. The rupture occurred at relatively shallow depth, which amplified ground motion on nearby land — and on Genkai Island in particular, which sat almost directly above the fault line.

The event fell in the 17th year of the Heisei era (平成, Heisei), the reign of Emperor Akihito, which ran from 1989 to 2019.

Why It Mattered

The 2005 Fukuoka earthquake overturned a regional assumption. A prefecture that had planned for typhoons and floods, not tremors, discovered that an unmapped offshore fault could produce magnitude 7.0 shaking directly beneath its largest city. The finding forced a revision of seismic hazard maps for northern Kyushu.

Genkai Island became the centre of the response. With nearly 80% of its housing stock heavily damaged or destroyed, the island's entire population was evacuated to Fukuoka City. The evacuation and eventual return of residents over the following years became a closely watched test of how Japan handled the recovery of a small, isolated community after a disaster — a question made urgent by the fact that the island's population was already ageing and declining before the earthquake.

The event also fed into a broader reassessment of seismic risk across Japan in the 2000s, a decade that included the 2004 Chūetsu earthquake and ended with the 2011 Tōhoku disaster. For Fukuoka, the practical legacy was concrete: stricter building standards, updated evacuation planning, and a permanent place for the Genkai Sea fault on the national seismic map.

The Name in Japanese

The Japanese name of the earthquake is 福岡県西方沖地震.

Kana reading: ふくおかけんせいほうおきじしん

Romaji: Fukuoka-ken seihō-oki jishin

The name is built from five elements, read in order:

福 — read fuku here. Meaning: fortune, good luck, blessing. This is the same character used in the place name Fukuoka.

岡 — read oka here. Meaning: hill, ridge, rising ground. Together, 福岡 (Fukuoka) is the prefecture and city at the centre of the event.

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

西 — read sei here. Meaning: west. This is the on'yomi, or Sino-Japanese reading; the native Japanese reading is nishi.

方 — read hō here. Meaning: direction, side. Combined, 西方 (seihō) means "the west" or "westward."

沖 — read oki. Meaning: offshore, open sea — the water visible from the shore, away from land. Japanese earthquake names use 沖 to mark an epicentre located under the sea rather than on land.

地震 — read jishin. Meaning: earthquake. 地 (chi, ji) means ground or earth; 震 (shin) means shake or tremor. The compound is the standard Japanese word for an earthquake.

Put together, 福岡県西方沖地震 translates literally as "Fukuoka Prefecture west offshore earthquake" — the earthquake off the western coast of Fukuoka Prefecture. The structure follows the standard Japanese naming convention for offshore quakes: place name, then direction, then 沖, then 地震. The same pattern appears in names such as 東北地方太平洋沖地震 (Tōhoku-chihō Taiheiyō-oki jishin), the 2011 Tōhoku earthquake.

Key Figures

• Date and time: 20 March 2005, 10:53:41 JST (01:53:41 UTC)
• Magnitude: MJMA 7.0 — the largest earthquake ever recorded in Fukuoka Prefecture
• Epicentre: 33.7383°N, 130.1750°E, in the Genkai Sea off the coast of Fukuoka Prefecture, Kyushu
• Deaths: 1 (an elderly woman)
• Injuries: over 1,200
• Houses damaged or destroyed: 20,300
• Worst-affected location: Genkai Island, where nearly 80% of homes were heavily damaged or destroyed
• Other affected prefectures: Saga, Nagasaki, Ōita and Yamaguchi
• Era: Heisei 17 (平成17年), the 17th year of the Heisei era