I haven't experienced too many myself. It was weird to feel my big, heavy bed shaking in all directions, but I was so tired at the moment, I had to double check online that I hadn't dreamt it when I woke up again later in the day x)

The earthquakes are usually pretty weak, and the ones you notice are more fun than frightening :)

When are you going to Japan?

I've spent some time in Japan, and have never experienced a really serious quake, so if you're just coming for a short vacation, you might not notice any at all.

You should be more worried about the heat, since you'll come in September ^^; It's usually still pretty hot that time of year. Hope you'll have fun though :)

It depends on which parts of the country you plan on going to. I can only speak for the Kanto area; in September leaves here are usually still green, and then start to turn red about mid-October. (it varies though. Last year the leaves were green longer)