Answer:
Faults.
Step-by-step explanation:
A fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep. Faults may range in length from a few millimetres to thousands of kilometres.
Like a kid and a big brother in the car on holiday, Suppose the big brother started an argument with the other sibling, they would say "It's your fault." As in, you started the argument and are responsible for admitting. Simple enough?
Now, take that concept and suppose the two are tectonic plates, when one pushes the other, it will shift and move the earth causing an earthquake.
This means that the faults are the border between the two plates (two brothers) that cause the argument to get physical as they shove into each other (tectonic plates to shift and overlap causing an earthquake).