Lateral offset · shear stress

Left-Lateral Strike-Slip

Dynamic model of an earthquake cycle on a left-lateral strike-slip fault. Elastic strain accumulates along the fault because it is locked due to friction. Once the strength of the rock is exceeded by the stress being applied to it, the elastic limit of the rock is reached and fault rupture begins (at the focus) and propagates along the fault. If the rupture reaches the ground surface the ground snaps (is offset) sideways (laterally). Stand on either side of the fault and look across to the block on the other side and that side moves to your left.

Video coming soon

Legend

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

Large blue arrows: shear stress acting on the crust

Bullseye: this block moves toward you

Asterisk: this block moves away from you

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

Locked, then loaded

Friction holds the fault in place while the crust on each side of the fault deforms elastically due to tectonic forces. As the crust bends and warps, it stores elastic strain energy for decades to centuries.

Rupture

The earthquake starts at the focus and propagates across part of the fault, the rupture surface, within seconds. Here it ruptures up to the entire surface trace. The amount of slip is patchy and falls to zero at the lower edge of the rupture surface at depth.

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.

Elastic rebound

The deformed warped rock rebounds (springs) back. Offset is greatest along and closest to the fault and smaller farther away, and anything built across it is severely damaged and torn apart.

Examples

Garlock Fault, California · 2019 Ridgecrest M6.4 foreshock, on a separate northeast-trending left-lateral fault

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