Normal Earthquakes

What I learned and first experienced in Japan was earthquakes. First time it happened, I was in class and just felt the shaking. It wasn't that bad but it was kind of surprising that no one said or reacted to it, besides our teacher say "え、地震”　(eh, earthquake). But it seems to be normal and happen all the time. This morning after I got up, I felt another one. There is no warnings or sirens(because it was too small). But it was a surprising for me, especially cause I never experienced it.