Mapped: M7.4 Earthquake Off Japan’s Sanriku Coast — Tsunami Warning for Iwate, Aomori, and Hokkaido

A magnitude 7.4 earthquake struck about 100 kilometres east-northeast of Miyako, Iwate Prefecture, at 16:53 local time (07:53 UTC) on Monday April 20, 2026. The quake hit at a depth of 35 km below the seafloor, according to the US Geological Survey — shallow enough to push a meaningful volume of water and trigger an immediate tsunami warning from the Japan Meteorological Agency.

This is the same stretch of coast — the Sanriku-oki subduction zone — that produced the 2011 Tōhoku earthquake and tsunami that killed more than 18,000 people. Today’s quake is roughly 1/200th of the energy released in 2011 (the Mw 9.0 release was almost 200 times larger), but the geography of the threat is identical: a near-shore offshore rupture sending waves directly at the densely populated coast within minutes.

Interactive Earthquake & Tsunami Warning Map

Click any city to see local shaking intensity (Modified Mercalli, MMI) and population. Click the blue tsunami zones for JMA’s wave-height warning by prefecture. The pulsing red marker is the epicenter.

Tsunami Warning Details

The Japan Meteorological Agency issued a tsunami warning within minutes of the rupture. The headline forecast: waves of up to 3 metres for the coastal prefectures of Iwate, Aomori, and Hokkaido. Lower-tier tsunami advisories cover Miyagi and Fukushima — the same coastal stretch hit hardest in 2011.

Local governments in Iwate, Aomori, Fukushima, Akita, Miyagi, and Hokkaido issued evacuation orders to coastal residents. JMA initially flagged that the earliest waves could reach the northern Iwate shoreline almost immediately, given the proximity of the rupture to the coast — and confirmed reports of tsunami arrivals in Iwate, Aomori, and Hokkaido within the first hour.

Where the Shaking Was Felt

Despite the offshore epicenter, perceived shaking reached MMI 6 (Strong) in two coastal communities — Noda and Kuji in northern Iwate. The USGS “Did You Feel It?” reports peaked at intensity 7.1 (Very Strong), confirming structural stress in the closest cities.

The single largest exposed urban area was Sendai (1.06 million residents), 200 km south of the epicenter — but it logged only MMI 4.1, equivalent to a noticeable rattle rather than damaging shaking. Closer to the epicenter, Aomori (425,000 residents) and Hachinohe (223,000) recorded the strongest shaking experienced by significant urban populations.

Why the Sanriku Coast Keeps Producing These Quakes

The Japan Trench, just offshore from Iwate Prefecture, is one of the most seismically active subduction zones on Earth. The Pacific Plate dives westward beneath the Okhotsk Plate at roughly 8 cm per year — and the locked sections release that strain in periodic megathrust earthquakes. The 2011 Tōhoku quake (Mw 9.0) ruptured the southern part of this trench. Today’s M7.4 sits in the same fault system but well to the north and at a fraction of the energy.

For perspective, in the past century the Sanriku-oki area has produced four earthquakes above M7.5 — in 1933 (M8.4, killed 3,068 in a tsunami), 1968 (M7.9), 1994 (M7.7), and 2011 (M9.0). A M7.4 is squarely within the expected return period for this stretch of coast — it isn’t a “surprise” event, it’s the kind of quake the region’s building codes and tsunami-evacuation infrastructure were designed for.

Early Impact and Damage Reports

Initial reports from JMA and Reuters confirm:

• Tsunami waves reported on the Iwate, Aomori, and Hokkaido coasts within the first hour after the rupture. No fatalities or serious injuries reported in the early hours.
• Tōhoku Shinkansen suspended for safety inspections; multiple coastal rail lines and several highways closed in the tsunami-warning prefectures.
• Evacuation orders issued by local governments in Iwate, Aomori, Fukushima, Akita, Miyagi prefectures and Hokkaido, covering coastal residents within JMA’s wave-height forecast areas.
• USGS PAGER alert: GREEN — the lowest of four colour-coded loss-estimate tiers. The model puts the most likely fatality count in the single digits and economic damage well below $100 million. The shallow offshore epicenter, the relatively modest magnitude (versus 2011), and the post-2011 building-code retrofits across the region are the dominant factors keeping the early projections low.
• No nuclear-plant incidents reported. The Onagawa, Higashidōri, and Fukushima Daiichi/Daini sites all sit within the affected coastline — JMA is monitoring; Tōhoku Electric Power has confirmed no operational changes at facilities currently in operation. (Fukushima Daiichi remains in long-term decommissioning.)

What to Watch Next

The first 24–48 hours will reveal three things: whether tsunami damage is contained to the predicted 1–3 m wave heights or exceeds them; whether aftershocks above M5 propagate north or south along the trench; and whether any coastal infrastructure (port facilities, fishing fleet, power substations) suffered damage that doesn’t show up in the initial post-event scan. Japan’s post-2011 monitoring infrastructure is the most sophisticated tsunami-detection network in the world — expect updated wave-height measurements within hours, not days.

For real-time updates, the JMA tsunami map and the USGS event page (linked in the sources below) are the authoritative feeds. We’ll update this article as the situation develops.

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