Casual is derived from Casualty. Casualty is a synonym of Disaster. Earthquake can cause/lead to Disaster. Earthquake is related to Shock. 
Festival is a type of Celebration. Festival is related to Party. Party is related to Christmas. Christmas is related to Birth. 
Casual --DerivedFrom--> Casualty <--Synonym--> Disaster <--Causes-- Earthquake <--RelatedTo--> Shock 
Celebration <--IsA-- Festival <--RelatedTo--> Party <--RelatedTo--> Christmas <--RelatedTo--> Birth 