Lower Grotto is the 15th province (Stage 1 Province 15) of the Oceanic Future, accessible (along with Walled Gulf) after taking control of Foam Ceiling to the southeast. Taking control of both Silver Swarms and Lower Grotto unlocks Rocky Domain.
If previous sectors acquired by negotiation:
It moved a few rocks, so that earthquake might actually have been helpful.
If at least one sector taken by force:
Even after the earthquake, how can you just drive away?
A storm is coming.