In 1895, geology professor Andrew Lawson was exploring the landscape near San Francisco when he noticed a strange, linear valley. He realized it was a massive fracture in the Earth’s crust and named it the San Andreas Fault. Initially, Lawson believed it was just a local feature. But he had uncovered something far more significant: the visible boundary between two colossal tectonic plates. To the west, the Pacific Plate grinds northwest, carrying part of California with it. To the east, the rest of the continent sits on the North American Plate. This immense fault line, stretching 1,280 kilometers through the state, wasn't just a geological curiosity. It was the source of California's violent earthquakes.
The San Andreas Fault: California's Sleeping Giant
The San Andreas Fault, the boundary where two tectonic plates grind past each other beneath California, and why scientists expect another big earthquake.
Chapter 1
The Hidden Crack
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Frequently Asked Questions
What is the San Andreas Fault?
It is a 1,280-kilometer fracture in the Earth's crust that forms the tectonic boundary between the Pacific Plate and the North American Plate in California. The two plates slide horizontally past one another along this line, causing earthquakes.
What caused the 1906 San Francisco earthquake?
The earthquake was caused by a sudden rupture along the northern section of the San Andreas Fault. Stress that had been building for decades was released, causing the ground to shift up to 6.4 meters and generating violent seismic waves.
What is the 'Big One'?
The 'Big One' refers to a hypothetical major earthquake, likely magnitude 7.8 or higher, that is expected to occur on the southern segment of the San Andreas Fault. This section has not ruptured in over 300 years and has accumulated significant stress.
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