tertremo

Build it and you have it: tero plus tremi plus -o, an earth-trembling. German does the same trick with Erdbeben and so does Dutch with aardbeving; English took the equally transparent "earthquake" and then hid a Greek word, seismo, behind it for every technical purpose. Esperanto has sismo too, and the geologists use it, but tertremo is what everyone else says.

The order of the parts is the usual one and it matters. The main root stands last, so the word is fundamentally a tremo, a trembling, and ter- says which kind. Read it the other way round and you would get a quake-shaped piece of ground, which is why the compounding rules insist on the direction. The same order gives terpomo, an earth-apple, which is a potato, and not an apple-shaped country.

For the vocabulary around it: sismologio is seismology, postskuo is an aftershock, and the verb for the ground doing it is simply la tero tremas. Note that the third example uses both, the verb and the compound, which is a good way to feel how the noun was made.