seo – Is there a structure for earthquake data?

No, there is no specific type for earthquake data.

I looked at the Event schema, and it looks like it’s entirely geared towards social events, not natural events.

And the Place schema doesn’t cover an earthquake either, because an earthquake is a Thing that happens at a Place, it’s not a Place in itself.

The most specific type you could use, in my opinion, is Thing.

I see that your question is tagged seo. If you’re looking to add structured data for SEO reasons, as Stephen mentioned in the comments Google does not support rich snippets for this data type, so marking this up can’t help your SEO.