They are both grammatically correct, but I think the second one is confusing.
If you are suggesting that people start to investigate so that they can figure out the cause of the accident, then sentence one says that more clearly.
Sentence two suggests that determining the cause of the accident is dependent upon them BEGINNING an investigation. I don't think that is what you mean. It's not beginning an investigation that matters it is the investigating that matters, therefore this should be your verb. .
The important act here is "investigating" and that is what must begin in order to find the causes.
Few people would think this type of nuance through and I appreciate the writer who is thinking like this. .
Leah G.
11d
Ethan B.
Thank you for your respone. I have one more question. Is this sentence more like the first one: "The archaeologist dives deep underwater to determine the condition of the ancient ship."11d