Tuesday April 18, 2006

The Day The Earth Shook

One hundred years ago, at 5:12 am on Wednesday morning, April 18, 1906, San Francisco (and other parts of northern California) endured the infamous San Andreas earthquake. Although the subsequent fire caused the most damage to The City, the quake was indirectly responsible for the devastation. Gas and water pipes burst during the shake, setting off fires for which there was no water available to quench the blaze. Ultimately, buildings were ordered to be dynamited in an attempt to stop the fire from continuing to spread.

The California earthquake of April 18, 1906 ranks as one of the most significant earthquakes of all time. Today, its importance comes more from the wealth of scientific knowledge derived from it than from its sheer size. Rupturing the northernmost 296 miles (477 kilometers) of the San Andreas fault from northwest of San Juan Bautista to the triple junction at Cape Mendocino, the earthquake confounded contemporary geologists with its large, horizontal displacements and great rupture length. Indeed, the significance of the fault and recognition of its large cumulative offset would not be fully appreciated until the advent of plate tectonics more than half a century later. Analysis of the 1906 displacements and strain in the surrounding crust led Reid (1910) to formulate his elastic-rebound theory of the earthquake source, which remains today the principal model of the earthquake cycle.

At almost precisely 5:12 a.m., local time, a foreshock occurred with sufficient force to be felt widely throughout the San Francisco Bay area. The great earthquake broke loose some 20 to 25 seconds later, with an epicenter near San Francisco. Violent shocks punctuated the strong shaking which lasted some 45 to 60 seconds. The earthquake was felt from southern Oregon to south of Los Angeles and inland as far as central Nevada.

[excerpt: The Great 1906 San Francisco Earthquake at the USGS Earthquake Hazards Program site ]

"In this one day the accumulation and accomplishment of years were swept away. The fire spread over only about one-sixth of San Francisco's total area, but destroyed all the central business portion of the city and a large residence district. Business blocks, factories, palatial homes, modern hotels, apartment and lodging houses disappeared.

"In this one day all class distinctions were leveled. And then here the great Lesson of Love was taught, and the best that is in Humankind rose above all pride of place and possessions. That was the flower that blossomed amid the city's ruins, and for it Glory be. The men and the women and the children forgot all personal loss, forgot their own sorrow in giving joy and comfort, coffee and buns and blankets, smiles and sturdy words of brave sympathy and of glad promise..."

[ Sunset magazine, 1906 Emergency Edition ]

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The Day The Earth Shook ( in category Noteworthy ) - posted at Tue, 18 Apr, 05:12 Pacific | «e»