This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
Refracted wave. Traveltime curves of the direct blue and critically refracted green wave At the bottom the according ray paths are displayed Laufzeitkurven der direkten und der refraktrierten Welle mit Strahlwegen unten und einigen Fachbegriffen own work created with Xfig orig April modified for englisch labels March Iwoelbern