@catsalad I've experienced two distinct varieties, both when I was living in Tokyo:

1. Everything begins slowly, subtly swaying, but the magnitude of the sway keeps increasing over a few minutes until it's too strong to stand up without falling over; things are falling off walls and furniture is toppling and you hear glass breaking and crashing noises and alarms going off. Then it gradually tapers off the same way it built up.

2. You can see a weird compression wave coming at you from the far distance, incredibly fast, like a visible sound wave in the ground. Then it hits you and there's a tremendous booming sound and the ground just moves suddenly sideways a few feet and everyone falls over, like a rug has been pulled out from under the whole world. And that's it. It's weird and singular and everyone gets back up, a bit disturbed and out of sorts.