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TITLE: Rocks That Break

Like a pane of glass dropped on the floor, some rocks are brittle: They break, or fracture, in response to stress. Rocks tend to fracture when stress is applied rapidly, at shallow depths, or at low temperatures. If rocks on each side of a fracture are displaced, the fracture becomes a fault. Earthquakes result from the brittle deformation that also creates faults.

[Photo: Slickensides]

The shiny surface on this slickensides was polished by fault movements.

[Photo: Limestone]

Movement in a fault zone chopped this layered limestone into pieces, which tilted like books on a shelf.

[Photo: Sandstone]

After pore water was driven out of this sandstone, it took up less space. More than 24 faults accommodated the loss in volume.

[Photo: Highway damaged by an earthquake.]

This road, which crosses a fault, moved 1.5 m during the 1992 Landers earthquake in southern California.


Smithsonian National Museum of Natural History