Fault lines are:

the crust of the lithosphere that has fractured along plate boundaries and ridges
the crust of the athenosphere that has fractured along plate boundaries and ridges
the crust of the biosphere that has fractured along plate boundaries and ridges
the crust of the kryosphere that has fractured along plate boundaries and ridges

the crust of the lithosphere that has fractured along plate boundaries and ridges

Explanation:

Fault lines, also known as geological faults, are fractures in the rock blocks that make up the earth's surface, causing them to suffer relative displacements in their structures. These fractures are almost always formed by the action of internal relief agents and can manifest both in areas under strong tectonism and in more stable regions. In other words, we can say that the fault lines are the crust of the lithosphere that fractured along the plate boundaries and grooves.