Here are two ways you can split a single audio file across multiple slides in Storyline:
Use the Built-In Audio Editor
One option is to import the audio file into all the related slides in Storyline, then use the audio editor to trim or crop the audio on each slide. See these user guides to learn more about using the audio editor in:
Use Articulate Presenter
If you need to split an audio file across numerous slides, you might find it faster to break it into individual tracks using Presenter 360 or Presenter '13, then import them into the corresponding slides in Storyline.