Along the coast of California, the tectonic plate
underlying the Pacific Ocean and the plate harboring the North American
landmass meet at the San Andreas Fault. Intense pressure builds up along the
fault as the two plates grind past each other, the Pacific Plate moving
northwest relative to the North American Plate. On the morning of April 18,
1906, the pent-up pressure was released in a major earthquake that thundered
across coastal California. The earthquake ruptured the ground for 296 miles
(477 kilometers) along the northernmost section of the San Andreas Fault,
and the ground surfaces on either side of the rupture slipped more than 20
feet away from each other in some places. The quake set off a catastrophic
fire in San Francisco that devastated the city.
This image shows the topography of the region using data from
NASA’s Shuttle Radar Topography Mission. Low elevations are green,
with yellow, pink, and white representing progressively higher elevations.
Major geologic faults are marked with white lines. The San Andreas Fault
runs in a northwest-southeast line along the coast. The numbers on the fault
line indicate how far the ground surface slipped at that location as a
result of the 1906 earthquake. Also labeled in the image is the Hayward
Fault on the eastern side of San Francisco Bay. The Hayward is one of the
faults with a high likelihood of a major earthquake in coming decades. That
fault runs through Oakland and Berkeley.