España: seísmo, terremoto y temblor.

I checked the words in a modern corpus of internet Spanish. A corpus is a giant database of words. It has 5.5 billion words in it. terremoto appears 140091 times sismo appears 127213 times temblor appears 37359 seísmo appears 8375 Conmoción does not mean earthquake. It means emotional shock or a concussion. Seísmo is an extremely uncommon word for earthquake. You probably don't want to use it. Terremoto will probably be understood and used everywhere.

Estoy en Argentina... aquí se conoce comúnmente como terremoto. Rara vez se lo llama sismo o temblor, y siempre se le agrega el grado en la escala de Richter. En los noticieros, las personas en la calle, entre amigos, etc. Suena extraño la idea de que alguien te comentara sobre que hubo un terremoto en alguna parte del mundo sin decirte al instante el grado. Saludos! xx

Thw general term for that is Sismobut when is a big one we tend to call is "terremoto" but if it's a small one we call it "temblor" although sometimes it is interchange the 3 terms. I hope that helps you. Saludos!