1993 Okushiri earthquake

What Happened

At 13:17:12 UTC on 12 July 1993, a magnitude 7.7 earthquake struck the Sea of Japan off the southwest coast of Hokkaidō, Japan's northernmost main island. The quake reached VIII (Severe) on the Mercalli intensity scale. Its epicentre lay at 42.851°N, 139.197°E, close to Okushiri, a small island lying west of the Hokkaidō mainland.

The shaking itself was destructive, but the tsunami it generated was worse. Waves struck the coastlines of Hokkaidō and travelled as far as southeastern Russia, killing people on both sides of the Sea of Japan. In total, 230 people died. Okushiri was the hardest-hit place: 165 of the dead were on that single island, killed by the earthquake, the tsunami, and a large landslide that followed.

The event took place in the fifth year of the Heisei era, the reign period of Emperor Akihito that ran from 1989 to 2019.

Background

The Japanese archipelago sits where four tectonic plates meet, and the resulting seismic activity is a permanent feature of life in the country. The Sea of Japan coast west of Hokkaidō had long been known as earthquake country, but the specific hazard that made 12 July 1993 so deadly was not the shaking — it was the water.

The earthquake's epicentre was offshore, in the sea rather than under land. When a large fault ruptures beneath the seabed, the sudden displacement of the ocean floor pushes the entire water column above it, sending waves outward in all directions. Those waves travel across open water at speeds comparable to a jet aircraft, then slow and steepen dramatically as they enter shallow coastal water, arriving as a wall of water with very little warning time. For a community on an island only a short distance from the epicentre, that warning time can be measured in minutes.

Okushiri is a small island in the Sea of Japan, positioned southwest of Hokkaidō and close to the epicentre of the 1993 event. Its geography — low-lying coastal settlements backed by steep terrain — left residents exposed both to the incoming waves and, in at least one case, to the landslide that the shaking triggered.

Why It Mattered

The death toll of 230, concentrated so heavily on one island, exposed how poorly prepared Japan's coastal communities were for a near-field tsunami — one generated so close to shore that there is almost no time between the earthquake and the arrival of the waves. Residents of Okushiri had minutes, not hours.

The disaster also demonstrated that a tsunami generated in the Sea of Japan does not respect national borders. Waves from the same event caused deaths in southeastern Russia, across the water from Hokkaidō. A hazard that had been understood primarily as a Japanese coastal problem was shown to be a regional one.

The earthquake and tsunami became a reference point in Japanese disaster planning for the remainder of the Heisei era. The pattern it established — a large offshore earthquake, a tsunami arriving within minutes, and the heaviest casualties on the nearest coastline — was studied and re-studied. When the far larger Tōhoku earthquake and tsunami struck the same country's northeastern coast in March 2011, the 1993 event was among the precedents that shaped how authorities and the public understood what a near-field tsunami could do.

For the residents of Okushiri, the date 12 July 1993 marks a permanent dividing line in the island's memory, the way a handful of dates do in every part of Japan.

The Name in Japanese

The Japanese name of the disaster is 北海道南西沖地震, read ほっかいどうなんせいおきじしん (Hokkaidō Nansei Oki Jishin).

Breaking it down:

北 — read ほく (hoku) here. Meaning: north. This is the same character that begins 北海道, the name of Hokkaidō.

海 — read かい (kai) here. Meaning: sea, ocean.

道 — read どう (dō) here. Meaning: road, way, or province. Together, 北海道 (Hokkaidō) literally means "northern sea circuit" — the name given to the northern region in the nineteenth century, modelled on the older Japanese administrative circuits.

南 — read なん (nan) here. Meaning: south.

西 — read せい (sei) here. Meaning: west. Together, 南西 (nansei) means "southwest."

沖 — read おき (oki). Meaning: open sea, offshore. In Japanese place and event names, 沖 specifies that something happened out in the water rather than on land — a distinction that matters enormously for an earthquake, because it is precisely the offshore location that produced the tsunami.

地震 — read じしん (jishin). Meaning: earthquake. 地 (chi, "ground, earth") plus 震 (shin, "shake, quake").

Put together, the name says exactly what happened: an earthquake in the sea southwest of Hokkaidō. Japanese disaster names are often built this way — a location marker followed by the type of event — so that the name itself carries the essential geography. English-language sources frequently shorten this to "the Okushiri earthquake," after the island that suffered most, but the Japanese name points at the sea, not the island.

Key Figures

Magnitude: 7.7 on the moment magnitude scale.

Maximum intensity: VIII (Severe) on the Mercalli intensity scale.

Date and time: 12 July 1993, at 13:17:12 UTC.

Epicentre: 42.851°N, 139.197°E, in the Sea of Japan off southwestern Hokkaidō.

Total deaths: 230, across Hokkaidō and southeastern Russia.

Deaths on Okushiri: 165, from the earthquake, the tsunami, and a large landslide.

Era: Heisei 平成, year 5 — the fifth year of the reign of Emperor Akihito, whose era ran from 1989 to 2019.