Refuges in one of the Army camps waiting for water.

On April 18^th, 1906, at 5:12 am, a major earthquake struck the San Francisco peninsula, California. The shaking lasted nearly a minute, and was felt as far away as Nevada. We now recognize that earthquakes are a common occurrence in California, but the residents of the young city of San Francisco were not so aware - the earthquake and subsequent fire destroyed much of the city, leaving more than half of the city’s 400,000 residents homeless.

The effects of the earthquake were studied in detail by scientists from the young universities in the area (J.C. Branner from Stanford University and Andrew Lawson from Berkeley) and across the country (notably H.F. Reid from Johns Hopkins and G.K. Gilbert from the U.S. Geological Survey). The group produced an exhaustive report in 1908, now commonly referred to as the Lawson report, which marks a major change in our understanding of earthquakes. Branner, Lawson, and their students were able to trace the fault rupture for hundreds of miles, leading to the recognition of the San Andreas Fault as a major structure, though the significance of this structure wouldn’t become completely clear until the advent of plate tectonic theory in the 1960’s. Detailed triangulation survey data, when compared with surveys taken prior to the earthquake, led Reid to formulate his theory of elastic rebound, which describes the basic mechanism by which stress builds up in the earth’s crust and is released through earthquakes. Additionally, the Lawson report detailed damage to buildings, noting for the first time that the amount of damage was strongly related to the quality of construction and the underlying material: buildings built on loose sediment were completely destroyed, while those anchored in bedrock survived with far less damage.

Despite the devastation it caused, the 1906 earthquake brought great insight into the way the earth works. The new understanding eventually led to the development of building codes and preparedness plans. Today, California is no less prone to earthquakes, but residents are far safer and more prepared than they were 100 years ago.

If you would like to read more about plate tectonics and earthquakes, visit our Plate Tectonics II lesson. 

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