Moderate territorial crisis: a single city secedes from your empire. It is chosen according to your stability map, so if available it will be a city on ahistorical territory.
Severe territorial crisis: "Collapse to core": if more than half of all non-core cities are ahistorical, all ahistorical cities will secede. Otherwise, all non-core cities will secede.
Moderate economic crisis: You lose gold equivalent to 50% of your research progress (sum of all techs which you have begun to research). If you do not have enough gold on treasury, the beakers invested in the techs will be subtracted directly.
Severe economic crisis: You lose gold equivalent to 100% of your research progress (see above). All your cottages downgrade one level. You lose all GP points in all cities.
Moderate domestic crisis: All unhappy cities will go into two turns of unrest.
Severe domestic crisis: Two turns of anarchy. All unhappy cities secede.
Moderate diplomatic crisis: Your relations with 2 civilizations will deteriorate.
Severe diplomatic crisis: Your relations with 5 civilizations will deteriorate. All your vassals are set free.
Moderate military crisis: The defense value of all cities with enemy claim is reduced to 0.
Severe military crisis: Two turns of unrest in all cities with enemy claim. You cannot move all military units for one turn.