Have yet to encounter an earthquake event, is there one?
Maybe an earthquake would level everything on random tile (city, improvement, forest, units, even a feature) and surrounding tiles suffer some damage.
Could have a chance of generating marble or mineable resource, earth elemental or earth mana. Also have a chance of turning tile into a hill tile (not sure if that would work for sea or ocean tiles but would be cool)
Unlikely to have an major effect early game but potentially significant later on
Could have lower chance of occurring in RoK lands, and if it does more likely to generate resource
Could even be a RoK ritual:-
Event; A Stonewarden shows remarkable aptitude in shifting the earth and believes with some further experiments and practice may be able to generate an earthquake to smite our enemies, do we fund further research?
Event; A Stonewarden intends to try to generate an earthquake but the consequences could be dire, do we allow the experiment to proceed? An earthquake strikes random tile within Empire and allows Earthquake Ritual
Ritual; Can cause an earthquake to strike random tile within given area (like hawk recon area). Maybe lowers all other civs attitude but doesn't cause war?
Sorry about the long rambling post

and I don't even know if any of that is doable
