In a theoretical Earth made of uniform glass, isoseismal lines would be perfect concentric circles. But real-world geology is messy. Faults rupture in specific directions (directivity), sending more energy one way than another. Furthermore, local soil conditions play a huge role; soft sediments can shake much more violently than hard rock. This means a town 50km away on soft soil might feel a higher intensity than a town 20km away on bedrock. These factors distort the lines into irregular shapes that map the complex relationship between seismic energy and the Earth’s varied surface materials.