Strange fault direction

Hello everyone, I am working with a PyLith simulation that involves a complex, non-planar (curved) fault. I’m currently trying to visualize the fault direction in ParaView. However, I get a result that seems non-intuitive, the arrows point in various directions. So I wonder, why is the direction so strange? Is it because of the curved surface? How can I address this?

The arrows indicate the dip direction on fault.

I find that this problem is caused by unsuitable up_dir value, change the up_dir I can get meaningful strike and dip direction.