to put it into perspective, Japan NORMALLY has approximately 1500 small earthquakes YEARLY, which is about 4 per days

but over 400 within 5 days? hmm, now let's take a look at this news from 2 months ago

>A government panel has revised its damage estimate for an anticipated mega-quake in the Nankai Trough off Japan's Pacific coast. It predicts that an earthquake of up to magnitude 9 will claim about 298,000 lives. Seismologists say there is a roughly 80 percent chance of such a quake occurring in the next 30 years.

I'll leave it to your interpretation.

https://www.data.jma.go.jp/multi/quake/index.html?lang=en
https://www3.nhk.or.jp/nhkworld/en/news/backstories/3910/