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The great San Francisco earthquake struck on Wednesday, April 18, 1906 at 5:12 am, with the offshore epicenter about 3 km (2 mi) south of the city. It ruptured 477 km (296 mi) along the San Andreas Fault. People felt shaking from Oregon in the Pacific Northwest to Los Angeles and from the inland to central Nevada. Its magnitude is estimated at 7.9, but values up to 8.25 have been proposed. The quake and resulting fire were one of the worst natural disasters in California. The death toll is estimated at over 3,000 people. After the earthquake, about 200,000 people were left homeless. Thousands camped at city parks in tents supplied by the Army.

At the time of the Great San Francisco Earthquake, instruments to measure earthquakes were non-existent in the area. Therefore, scientists who measure earthquakes that happened before 1900 review historical accounts of damage to buildings, the distance at which people felt tremors from the epicenter, and reports on changes in the soil. From this information they try to determine the intensity and magnitude of the earthquakes.

This post is part of Exploring Earthquakes, a rich collection of resources co-presented by the California Academy of Sciences and KQED. This material is also available as a free iBooks textbook and iTunes U course.

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Exploring Earthquakes RR

Exploring Earthquakes

Get a new perspective on earthquakes with this rich collection of multimedia resources. You'll learn why earthquakes happen, how they've shaped the Bay Area, and what you can do to prepare for the next one.