Terragen does not have procedural l-system type noises so you might want to sample some photo-stock noises similar to these painting and layering them over a huge map in something like Photoshop or use some type of texture editor assuming it can do such fractal types and spherically wrap it all over a Terragen Planet Object using different inputs within the nodes like image to displacement, color and so on.
It is clear here that these patterns are traveling in many directions and have layers to them.
