First Blush

Reflections and sightings from [almost] daily jogging at dawn

Tuesday, April 18, 2006

Sunrise 6:30 am: Nine seconds later on April 18, 1906

The Dawn Joggers hit the bike path just moments after 6:12 this morning, 100 years after the Great Quake struck. While the annual commemoration took place in darkness around Lotta's Fountain in downtown San Francisco this morning at 5:12 am, it would actually have been light when the San Andreas fault ruptured a hundred years ago as there was no daylight savings time. The sun would have risen about 15 minutes later, at 5:30 (today's 6:30 PDT) and peaked through the open fields of the Peninsula much like it appears in today's photo.

The female DJ (and Bay Area native) grew up hearing that the epicenter of the Great Quake was north of San Francisco in the Marin County town of Olema. Modern scientific measurements changed that to just off Daly City some years ago and, more recently, to off Ocean Beach in San Francisco. That's about where the San Andreas fault moves out to sea for a stretch of miles before returning to land in Marin. The shaking would have started in Menlo Park about nine seconds after the initial rupture. The U.S. Geological Survey put together a nifty ground motion simulation map, with the most violent shaking appearing in red. See it here.


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