A thrust fault is a reverse fault with a gentle dip, about 30° or less (here 30°). The hanging wall rides up and over the footwall, stacking older rock on top of younger rock.
Video coming soon
Legend
HW: hanging wall, the block above the fault
FW: footwall, the block below the fault
Epicenter: the point on the ground directly above the focus
Focus (hypocenter): location on the fault where the rupture initiates
Small black arrows: how the blocks move relative to each other
Triangles: reverse or thrust fault, on the hanging wall (indicating the uplifted block)
Large blue arrows: compressional stress acting on the crust
Fault plane (pink)
Rupture surface: the part of the fault that slipped
Rupture front, spreading out from the focus
Fault slip magnitude arrows: blue (most slip) to yellow (least)
Road
Aqueduct (concrete channel)
Railroad
Power line
Electrical arcing where the power line snaps
Flooding from the broken aqueduct
House: a wood-frame home, flexible enough to sway and ride out the shaking
Brick building: three stories of unreinforced brick and masonry, brittle, so it collapses into rubble during strong shaking
Industrial complex: built right across the fault, so the rupture tears it in half and the bays beside the break collapse
Leeper's Awesome 2016 Tacoma
Passenger train: a diesel engine pulling three passenger cars
What moves
The hanging wall slides up a gently sloping fault, over the footwall.
What causes it
Strong compression, as in mountain belts and subduction zones.
Seismic waves
As the rupture spreads, every part of the fault that slips generates seismic energy that radiates out from the fault surface as seismic waves.
Blind thrusts
Some thrusts never reach the surface. The 1994 Northridge M6.7 earthquake was on one.
Examples
1971 San Fernando (Sylmar), M6.6, on an oblique thrust fault (thrust with some left-lateral slip) · 1999 Chi-Chi, Taiwan, M7.7
Biggest earthquakes
Subduction megathrusts are giant thrust faults, like the one behind the 2011 Tohoku, Japan, M9.0.
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