An earthquake. This is the same thing as an earthquake — it is not a small one or a special kind. It is just another word for it, borrowed from Spanish. You will meet it almost only in American news writing, and mostly in California and other places in the American West where Spanish words are part of everyday life and earthquakes are common. Newspapers like it because it is short and lets them avoid saying "earthquake" three times in one story. Nobody says it in normal speech — if the ground shakes, an American will say "Did you feel that earthquake?", never "Did you feel that temblor?". So think of it as a newspaper word. Some writers use it for a smaller shake and save "earthquake" for a big one, but that is their own habit, not a rule, and dictionaries do not agree on it. The plural is "temblors".

地震（美國報紙用語，尤其加州；就是 earthquake，不是另一種地震）