Japan's crustal activity has indeed become highly active in recent months. Since the beginning of this year, the frequency of strong earthquakes has increased significantly compared to previous years, with multiple scholars and official agencies warning that tectonic activity in certain regions has entered a dangerous phase.
According to the latest observational statistics from the Japan Meteorological Agency, from January through early May 2026, the cumulative number of earthquakes with a seismic intensity of 4 or higher nationwide has reached 21 — nearly double the count from the same period last year. In April alone, five tremors of intensity 5 or stronger occurred. Meteorological experts widely believe that such intense seismic clustering represents a "red alert" for increasingly active crustal movement, and could be a precursor to a potential mega-quake.
Northeast Japan: A Potential M8 Earthquake Within One Year
According to a report by Japanese media, Professor Emeritus Junzo Kasahara of the University of Tokyo, a leading authority on marine seismology, has identified the waters off the Sanriku coast in northeastern Japan extending to Hokkaido as the most concerning region. The significant activation of the Pacific Plate led to successive strong earthquakes in late April, including a magnitude 7.7 offshore Aomori on April 20 and a magnitude 6.2 offshore Tokachi, Hokkaido, on April 27.
Drawing on historical records, Kasahara noted that following a large earthquake in this area, there is often a chain reaction of even larger quakes within one year. He has not ruled out the possibility of a magnitude 8 mega-quake occurring within the next year, which would generate a tsunami up to 10 meters (33 feet) high, posing a catastrophic threat to coastal areas.
Kanto Region: The "Mysterious Earthquake Cycle" and Tokyo Direct-Beneath Threat
Beyond the northern threat, Toshiyasu Nagao, President of the Japan Earthquake Prediction Society, has raised concerns about the Tokyo metropolitan area. He identified a "mysterious earthquake cycle" of approximately 37-38 years offshore the Boso Peninsula in Chiba Prefecture. With 39 years having passed since the last major quake in 1987, the region has already entered a critical stage. Historical data show earthquakes in the area in 1912 (magnitude 6.2), 1950 (magnitude 6.3), and 1987 (magnitude 6.7).
If the Boso Peninsula region experiences an earthquake of magnitude 7, the resulting crustal stress could directly trigger adjacent plate movements, potentially inducing a catastrophic direct-beneath-Tokyo earthquake. Given Tokyo's extremely dense population and aging infrastructure, the consequences could be devastating.
Nankai Trough: Government Raises Probability for Mega-Quake
Most concerning for the Japanese government is the situation along the Nankai Trough. Recent strong earthquakes extending from the Noto Peninsula to Nara indicate intense stress release within the Philippine Sea Plate. The government has raised the probability that a major earthquake will occur immediately after the issuance of a "Nankai Trough Earthquake Emergency Information" alert from "one in roughly ten-plus" to "one in ten".
In March 2026, Japan's Cabinet Office published updated earthquake simulation data, significantly revising upward the risk estimation of a large-scale earthquake occurring within one week following the issuance of a Nankai Trough Earthquake Emergency Information bulletin. Under the highest-level "Megathrust Earthquake Alert," the probability of a magnitude 8 or higher earthquake has increased from the original 7 percent to 10 percent.
Experts warn that while the Nankai Trough region historically experienced earthquakes in segmented ruptures, the latest data suggests that existing buffer boundaries may have disappeared, significantly increasing the likelihood of a "full-zone simultaneous rupture" next time. Such an event would involve an earthquake moment magnitude and tsunami energy far exceeding historical records, with projected deaths potentially reaching 300,000. The Cabinet Office noted that the probability of a magnitude 8-9 earthquake occurring along the Nankai Trough within the next 30 years is now estimated at 80 percent.
The government emphasized that even a 1 percent probability is significant, ten times higher than the normal baseline probability of approximately 0.1 percent. Residents have been urged to confirm evacuation routes, secure furniture, and stockpile emergency supplies.
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