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The Rest of the Story: What's Happening at the Atomic Scale During Faulting?
by Stephen Marshak
To fully understand the process of faulting, we need to examine the behavior of atoms during the development of a fault. Recall that chemical bonds hold the atoms making up the minerals in rock together. We can picture these bonds as tiny springs. A chemical bond, like a spring, has a specific length when not subjected to a force. The application of a small stress to a rock causes the bonds to begin to stretch—the same process happens when you pull on the ends of a spring—creating an elastic strain; if you remove the stress, the bonds return to their normal length. But if instead you increase the magnitude of the stress, the bonds stretch further until eventually they break. If many bonds break along a surface in a mineral, a crack develops, across which the two halves of the mineral no longer connect. If the stress becomes larger still, the crack grows, and eventually more cracks form and grow until they all link together to form a single large fracture. When this happens, the rock as a whole divides into two, and one piece can slip past the other.
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