San Andreas Fault
A roughly 1,300 km transform fault in California where the Pacific Plate slides past the North American Plate, producing frequent large earthquakes.
Transform fault: A plate boundary where two plates slide horizontally past each other, neither created nor destroyed. The San Andreas is the archetype of this boundary type; its mechanics are the mechanics of transform boundaries.
1906 San Francisco earthquake: A magnitude 7.9 earthquake rupturing about 477 km of the northern fault, destroying much of San Francisco by fire. The rupture that first mapped the fault across hundreds of kilometres and linked faults to earthquakes.
Earthquake engineering: The design of buildings and infrastructure to survive strong ground shaking and fault displacement. California's seismic codes, the world's strictest, grew directly out of San Andreas earthquake losses.
Farallon Plate: A mostly subducted oceanic plate that once lay beneath the eastern Pacific and drove western North American tectonics. Its consumption replaced subduction along California with Pacific-North American strike-slip motion.
Earthquake prediction: The attempt to specify the time, location and size of a future earthquake, still not achieved reliably. Decades of San Andreas monitoring, including the Parkfield experiment, have not enabled short-term prediction.
Strike-slip fault: A fault where blocks move mainly horizontally, offsetting landscape features sideways rather than vertically. The San Andreas is a right-lateral strike-slip fault; streams and fences across it are visibly offset.
1857 Fort Tejon earthquake: A magnitude 7.9 earthquake rupturing the southern San Andreas from Parkfield to near San Bernardino. The last great rupture of the southern section, which has been locked and accumulating strain since.
Seismology: The scientific study of earthquakes and the elastic waves they generate through Earth's interior. The 1906 rupture created the field's founding dataset and its first fault-rupture measurements.
East Pacific Rise: The mid-ocean ridge along which the Pacific Plate spreads away from neighboring plates in the eastern Pacific. As this ridge was subducted, it created the triple junctions bounding the San Andreas today.
Seismic gap hypothesis: The idea that fault segments with no recent large earthquakes are likely sites of the next rupture. The southern San Andreas is the classic gap, yet its silence has lasted longer than the hypothesis predicts.