Japan

Japan Mainshock Forecasts

Northern Honshu

Official research shows that a megaquake is likely to hit Northern Honshu in the near-term and Japanese authorities have already warned their people to be prepared (Megaquake advisory ended in Japan, but officials say disaster risk remains | NHK WORLD-JAPAN News).

From independent research, www.mainshockearthquakes.com, this author forecasts : a possible M 8.5 megaquake on around May 19 ±2 days, with a 95% probability that the magnitude will fall between M 8.4 and M 8.6.

This updated forecast (May 1 UTC) is based on ten estimates from the author’s various research analytical modules (Ecological Model Overview) for the magnitude and/or timing of this anticipated megaquake, with supporting graphs and information to follow below.

Honshu’s previous M 9.1 Great Tohoku Earthquake [2011] is compared with current seismic data in the following way:

the first set of four graphs [Fig 1, below] examines:

(a) the magnitudes of these quakes, and
(b) their timing,

—all within a 750 km radius of the previous M 9.1 epicentre. The analysis is organized according to New Moon to New Moon (NM-NM) monthly intervals—this timeframe was selected because the 2011 M 9.1 Great Tohoku Earthquake occurred during a NM period, and the anticipated 2026 M 8.5 megaquake is also expected within this window.

Graph of largest monthly earthquakes in each New-Moon to New-Moon period before the Great Tohoku Quake, of 2011. Plots largest earthquakes in each NM-NM cycle from Jan 2010 to the M9.1 earthquake in 2011, and fits ecological-model triangle to data
Line graph showing the 750 NM-NM magnitudes of a Northern Honshu earthquake in 2026, with a blue line indicating daily magnitude fluctuations since January 1, 2025, and red annotations including a major magnitude of 8.6 on May 19, 2026.

The further graphs/figures supportive of this forecast to be added soon..

Updated May 1, 2026