1993 Kushiro-Oki earthquake

What Happened

At 8:06 pm Japan Standard Time on 15 January 1993, an earthquake struck off the eastern coast of Hokkaidō, the northernmost of Japan's four main islands. The epicentre lay at 42.92°N, 144.3533°E, in the Pacific Ocean near the town of Ashoro. The rupture released energy measured at magnitude 7.6 Mw, or 7.8 on the Japan Meteorological Agency's own scale (MJMA).

Shaking reached a maximum intensity of IX — "Violent" — on the Mercalli intensity scale, a measure of ground motion as experienced by people and structures rather than of raw energy released. The tremors were felt across the whole of Hokkaidō and reached into northern Honshu, the main island to the south, as well as Sakhalin and the Kuril Islands to the north and east.

Two people were killed. More than 600 were wounded. The earthquake struck in the fifth year of the Heisei era (平成, へいせい, the reign name of Emperor Akihito, 1989–2019), a period that would become one of the most seismically destructive in modern Japanese history.

Background

Japan sits on the boundary of four tectonic plates, and Hokkaidō in particular lies where the Pacific Plate dives beneath the Okhotsk Plate along the Kuril–Kamchatka Trench. This subduction zone generates frequent large earthquakes, and the offshore region east of Kushiro — the area the Japanese name Kushiro-Oki refers to — is one of the most active segments.

The 1993 event was not an isolated shock. It was one of two large earthquakes to strike Hokkaidō within the same calendar year. Six months later, in July 1993, a magnitude 7.7 earthquake occurred in the Sea of Japan off the island's western coast. That second event triggered a deadly tsunami and killed over 200 people, with many more recorded missing.

The two earthquakes differed in more than location. Although the July event killed far more people, it was felt over a smaller area than the January earthquake. A likely explanation is depth of focus: the later earthquake originated deeper in the crust, so its surface shaking was more tightly concentrated, whereas the January rupture transmitted perceptible motion across a much wider region.

Why It Mattered

The January 1993 earthquake demonstrated how far a single Hokkaidō rupture could project its effects. Shaking was recorded not only throughout Hokkaidō but into northern Honshu and across international borders into Sakhalin and the Kuril Islands — territory that had been under Soviet control, and after December 1991 under Russian control. For a region with sparse population and long distances between settlements, the breadth of the felt area was notable.

The casualty pattern also mattered. Two deaths and more than 600 injuries from a magnitude 7.6 event reflected both the strength of the shaking and the vulnerability of infrastructure in eastern Hokkaidō at the time. The Mercalli intensity of IX indicates damage to poorly constructed buildings and considerable disruption to ordinary life.

The pairing of the two 1993 earthquakes shaped how seismologists and emergency planners in Japan thought about Hokkaidō's exposure. A single year produced one shallow offshore rupture felt across a vast area and one deeper sea-floor rupture that generated a lethal tsunami. The two events together underlined that the island faced distinct hazards from different directions — the Pacific to the east and the Sea of Japan to the west — and that the depth of an earthquake's focus could determine whether the danger came from shaking or from water.

The Name in Japanese

The Japanese name of the earthquake is 釧路沖地震. Its kana reading is くしろおきじしん, and its romaji is Kushiro-Oki Jishin.

The name is built from four kanji, and each one carries a distinct piece of meaning:

釧 — read kushi here. This character originally denotes a bracelet or armlet, a metal ornament worn on the wrist. In this name it appears only as part of the place name Kushiro; it carries no independent meaning in the earthquake's name.

路 — read ro here. This character means "road," "path," or "route." Together with 釧 it forms 釧路 (Kushiro), the city and region on Hokkaidō's eastern coast. The two characters combined are a phonetic and semantic rendering of the Ainu place name, not a literal description of a "bracelet road."

沖 — read oki here. This character means "open sea," "offing," or "offshore." It is the key geographical word in the name: it tells the reader that the earthquake's epicentre lay out in the ocean, away from land, rather than directly beneath a town. Japanese earthquake names use 沖 frequently for offshore events, and it is the same character found in names such as 東北地方太平洋沖地震 (Tōhoku-chihō Taiheiyō-oki Jishin, the 2011 Tōhoku earthquake).

地震 — read jishin. This two-character compound means "earthquake." 地 (chi, "ground," "earth") plus 震 (shin, "shake," "tremor") produces the standard Japanese word for an earthquake, used in both everyday speech and official seismological naming.

Read as a whole, 釧路沖地震 means "the Kushiro offshore earthquake" — the earthquake whose epicentre lay in the sea off Kushiro. The structure is typical of Japanese earthquake naming: a place name, followed by 沖 if the rupture was offshore, followed by 地震.

Key Figures

Magnitude: 7.6 Mw (moment magnitude scale); 7.8 MJMA (Japan Meteorological Agency scale).

Date and time: 15 January 1993, at 11:06 UTC, which is 8:06 pm Japan Standard Time.

Epicentre: 42.92°N, 144.3533°E, offshore in the Pacific Ocean near Ashoro, eastern Hokkaidō.

Maximum intensity: IX (Violent) on the Mercalli intensity scale.

Deaths: 2.

Injured: more than 600.

Area of felt shaking: throughout Hokkaidō, into northern Honshu, and across to Sakhalin and the Kuril Islands.

Era: Heisei 5 (平成5年), the fifth year of the Heisei era.

Related event: a magnitude 7.7 earthquake in the Sea of Japan six months later, which triggered a tsunami and killed over 200 people, with many missing.