The word, initiate, means to begin or commence. We can initiate a conversation when we take the first step to talk to someone. However, our attempts might fail. We might initiate a conversation with someone but it goes nowhere if they don't respond.
The word, trigger, means an act that sets a series of events in motion. Saying, a simple "hello" to someone might trigger a long and fruitful conversation.
If you are talking about a fault or fault line that is a break in the layers of rock , you can say, that the pressure triggered an earthquake and series of aftershocks.
Hope this helps