Will a 6.0+ magnitude earthquake occur in Japan this month?

Analysis

As of October 7, the USGS catalogue showed no magnitude 6 or larger earthquakes in the October window, which runs from 12:00 AM ET on October 1 to 11:59 PM ET on October 31. The largest Japan-region event listed so far was a magnitude 5.5 shock near the Volcano Islands on October 4, recorded at a depth of 10 kilometres. Other Japan events in the records were smaller, including a magnitude 4.7 event north-northeast of Yonakuni and a magnitude 4.8 event south of Koshima. The forecast leans toward Japan not recording a qualifying quake, though only modestly. About 592 hours of the window remain, so there is plenty of time for one to occur. Earthquakes of this size are not predictable, and a single event could change the outcome. The supplied records give a global picture rather than a Japan-specific one. Over the past 365 days, magnitude 6 or larger events worldwide averaged 0.37 per day. The question needs one of those to be attributed by USGS to Japan, which is a much narrower target than the worldwide count. The research here does not provide a Japan-only frequency, so that comparison cannot be made precisely. Japan's Meteorological Agency reported after its September 7 Nankai Trough review that it saw no unusual change suggesting a higher-than-normal chance of a major quake there. That finding covers one region and does not rule out a magnitude 6 event elsewhere in the country. Revisions to magnitude or country attribution count only until the end of the third calendar day after an event. So the thing to watch is any USGS listing of a magnitude 6.0 or higher event in Japan, and whether its preferred magnitude holds through that revision period.