Event is a synonym of Consequence. Consequence is a type of Significance. Significance is a type of Meaning. Meaning is related to Reply. 
you would Thank because Grateful. Thanks is a form of Thank. Thanks is related to Reward. Reward is related to Positive. 
Event <--Synonym--> Consequence --IsA--> Significance --IsA--> Meaning <--RelatedTo--> Reply 
Grateful <--MotivatedByGoal-- Thank <--FormOf-- Thanks <--RelatedTo--> Reward <--RelatedTo--> Positive 