2023 Noto earthquake

What Happened

On 5 May 2023, a strong earthquake struck off the coast of Ishikawa Prefecture, Japan. The Japan Meteorological Agency measured the main shock at MJMA6.5, while a moment magnitude of Mw6.3 was also assigned. The epicenter lay in the Sea of Japan, 49 kilometres (30 miles) northeast of Anamizu in Hōsu District, with the town of Suzu closest to the rupture.

The event was part of a larger seismic sequence known as the Noto earthquake swarm. This swarm had been producing persistent earthquake activity in the region for some time, and the May shock was its most powerful event up to that point. The earthquake occurred during the Reiwa period, in the fifth year of the Reiwa era.

Background

The Noto Peninsula projects northward into the Sea of Japan from the main island of Honshu. Its coastal waters sit above a complex network of active faults, where the crust has been under strain for decades. Beginning in late 2020, the region experienced a marked increase in seismic activity, with thousands of small tremors recorded in a pattern scientists classified as an earthquake swarm.

Unlike a typical mainshock-aftershock sequence, a swarm produces many earthquakes of similar size over an extended period without a single dominant event. The 5 May 2023 earthquake broke that pattern, delivering a shock far larger than anything the swarm had previously generated. The town of Suzu, located on the peninsula's northeastern coast, bore the closest proximity to the epicenter and experienced the strongest shaking.

Why It Mattered

The earthquake demonstrated that the Noto swarm could produce damaging, moderate-to-large events, not merely minor tremors. Its location offshore, near a populated coastline, meant that ground shaking reached communities quickly and with little warning. The event also raised concerns about the potential for even larger earthquakes in the same fault system, a question that would prove tragically relevant later in the year.

For researchers, the May shock provided critical data on how swarm activity can evolve into a major rupture. It highlighted the difficulty of forecasting whether a swarm will escalate, since the physical processes driving the Noto sequence remain only partially understood. The earthquake also underscored the vulnerability of rural coastal towns like Suzu, where older buildings and infrastructure may not withstand strong shaking.

The Name in Japanese

The Japanese name for this earthquake is 奥能登地震. Its kana reading is おくのとじしん, and in romaji it is written Oku Noto jishin.

The name breaks down into three components:

• 奥 (おく, oku): meaning "inner" or "deep." In geographical terms, it refers to the far or remote part of a region, away from the main population centers.
• 能登 (のと, Noto): the name of the Noto Peninsula, the landform projecting into the Sea of Japan where the earthquake occurred. The characters themselves are ateji, chosen for sound rather than meaning, so they do not carry a semantic gloss in this context.
• 地震 (じしん, jishin): meaning "earthquake." The first character, 地 (じ, ji), means "ground" or "earth," and the second, 震 (しん, shin), means "to shake" or "tremble." Together they form the standard Japanese word for an earthquake.

Thus 奥能登地震 literally reads as "Inner Noto Earthquake," identifying the event by its location in the northeastern part of the Noto Peninsula, the area known as Oku Noto. The name distinguishes this event from other earthquakes in the same region, such as the larger shocks that would strike the peninsula later in 2023 and in 2024.

Key Figures

• Date: 5 May 2023
• Magnitude: MJMA6.5 (Japan Meteorological Agency scale); Mw6.3 (moment magnitude)
• Epicenter: Sea of Japan, 49 km (30 mi) northeast of Anamizu, Hōsu District, Ishikawa Prefecture
• Nearest town: Suzu, Ishikawa Prefecture
• Coordinates: 37.54° N, 137.305° E
• Seismic sequence: Part of the Noto earthquake swarm
• Period: Reiwa era, year 5 (令和5年)