Japan’s offshore magnitude-7.7 earthquake off northern Iwate Prefecture is being assessed as a moderate loss event so far, while authorities warn that seismic risk remains elevated in the near term. The quake struck in Pacific waters off northern Iwate at 4:53pm on Monday, April 20, shaking buildings over a wide area and moving high-rises in Tokyo, several hundred kilometres from the epicentre, according to the Japan Meteorological Agency (JMA), as reported by Japan Today.
By early Tuesday, at least six people had been reported injured, including two in serious condition, the Fire and Disaster Management Agency (FDMA) said, as reported by Inquirer. The agency reported no fires or damage to key facilities immediately after the event, and no large-scale disruption to critical infrastructure had been confirmed as of Tuesday morning. Chief Cabinet Secretary Minoru Kihara told a news conference that there were no immediate reports of serious injuries or significant structural damage, while adding that the government continued to gather information from local authorities and operators of important facilities.
The earthquake triggered tsunami warnings and advisories along parts of the northeastern Pacific coast. The JMA initially warned that tsunami waves could reach up to three meters, leading coastal municipalities to implement emergency protocols and open evacuation sites. Around 40 minutes after the main shock, an 80-centimeter (31-inch) tsunami reached the port of Kuji in Iwate Prefecture. Smaller waves were recorded at other points along the coast of northern Japan. Municipalities in the affected areas issued non-compulsory evacuation directives for more than 182,000 residents, according to the FDMA.
As sea levels stabilized and no larger waves were observed, authorities downgraded tsunami warnings to advisories, indicating the potential for waves of up to one meter in parts of Hokkaido, Aomori, Iwate, and Fukushima prefectures. All tsunami advisories were lifted around midnight, according to domestic media reports, and normal marine and port operations were progressively restored. Footage from national broadcaster NHK from several ports in Iwate showed no clearly visible extensive damage to port infrastructure, though inspections of coastal facilities, vessels, and cargo areas were still ongoing, and insurers were expected to rely on on-the-ground surveys to validate early impressions.
Within hours of the event, the JMA issued a special advisory indicating a higher-than-usual probability of another large earthquake. The agency said that “the likelihood of a new, huge earthquake occurring is relatively higher than during normal times.” The JMA emphasized that the advisory reflects a shift in probability and does not represent a specific forecast for a particular fault segment or timeline. “Although the probability is low, there is a possibility of another major earthquake occurring; therefore, please review your earthquake preparedness measures in these areas,” it said in a statement.
Prime Minister Sanae Takaichi said the prime minister’s office had established a crisis management team and was working to verify any casualties and property damage. “For those of you who live in areas for which the warnings have been issued, please evacuate to higher, safer places,” Takaichi said. Officials also warned that aftershocks could continue over the coming week, especially within the next two to three days. Authorities noted that some aftershocks could produce stronger shaking in specific locations than the initial quake, depending on depth and distance from populated areas, a factor relevant for both life safety and potential incremental damage to already stressed structures.
For Japan’s insurance market, the event is being considered both as a discrete loss and as part of a sequence of elevated seismic signals in recent years. Initial information suggests that insured losses from Monday’s quake and associated minor tsunami are likely to remain contained relative to the country’s largest historical catastrophes, assuming no significant aftershock occurs. However, the JMA’s indication of an increased chance of a magnitude 8.0 or stronger event is expected to focus attention on catastrophe modelling assumptions, aggregate limits, and reinsurance structures. Market participants are likely to:
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The advisory follows earlier week-long “megaquake” alerts tied to major tectonic zones. In 2024, the JMA issued its first special advisory for a possible megaquake along the Nankai Trough, an 800-kilometer undersea trench where the Philippine Sea plate is subducting beneath the Japanese landmass. Government scenarios for a large Nankai event and resulting tsunami project up to 298,000 fatalities and around US$2 trillion in economic losses. Another week-long advisory was issued in December 2025 after a magnitude-7.5 quake off the northern coast injured more than 40 people but caused no major structural damage.
Japan lies at the junction of four major tectonic plates along the Pacific “Ring of Fire” and records about 1,500 earthquakes a year, representing roughly 18% of global seismic activity by count. Many of these events are small, but outcomes depend heavily on the location and depth of the epicentre and the concentration of people and assets in affected areas. The 2011 magnitude-9.0 undersea earthquake and tsunami, which killed or left missing around 18,500 people and led to a meltdown at the Fukushima Daiichi nuclear power plant, remains a central reference point for how the insurance sector assesses earthquake and tsunami risk in Japan. That catastrophe led to significant changes in how carriers and reinsurers evaluate quake-tsunami correlation, nuclear-related exposures, contingent business interruption, and supply chain vulnerability.
