Fault types
A fault is a fracture where blocks of rock have moved past each other. How they move depends on whether the crust is being stretched, squeezed or sheared.
Stretching: the hanging wall slides down the fault.
Normal faults — stretching
When crust is pulled apart, the block above an inclined fault — the hanging wall — slides down relative to the footwall. Normal faults shape rift valleys such as the East African Rift and the Basin and Range of the western United States.
Reverse and thrust faults — squeezing
When crust is compressed, the hanging wall is pushed up. Low-angle reverse faults are called thrusts; the giant megathrusts at subduction zones produced the M9.1 Tōhoku (2011) and M9.5 Chile (1960) earthquakes.
Strike-slip faults — shearing
Here blocks slide horizontally along a near-vertical fault. Stand on one side: if the far side moves to your right it’s right-lateral, like the San Andreas; to your left, it’s left-lateral. The 2023 Türkiye earthquakes ruptured strike-slip faults more than 300 km long.
Why it matters
Fault type controls how the ground shakes and whether the sea floor moves vertically — the key ingredient for a tsunami.