Tuesday, December 20, 2005


Centennial of 1906 San Francisco Earthquake

There is an increasing amount of activity in the Bay Area due to the approaching centennial of the 1906 San Francisco earthquake. The Great San Francisco Earthquake occurred at 5:12 AM on April 18, 1906. On that day a 290 mile long section of the San Andreas fault moved (from Cape Mendocino in the north to San Juan Bautista in the south). The magnitude 7.7-7.9 quake and the following fire resulted in at least 700 deaths, and more likely 2000-3000. For comparison the well-known 1989 Loma Prieta earthquake had a rupture length of around 25 miles and a magnitude of 7.0. Earthquakes like the 1906 event happened in the past, and they will happen in the future. The plate motions that caused earthquakes in the past are still occurring. The Pacific plate is still moving north relative to the North American plate, and most of the motion is taken up by a fault that is a member of the San Andreas system. If an event like the 1906 earthquake were to occur today an estimated 155,000-160,000 households (not people) would be displaced, with the potential for great loss of life.

The 1906 Earthquake Centennial Alliance is a coalition of a huge number of universities, federal, state, and local governmental bodies, museums, parks, and businesses. This alliance hosts speakers, puts together museum displays, and so on. It’s well worth visiting their website if you live in an area that’s prone to earthquakes (or if you’re curious about places like that).

The San Andreas fault generally gets most of the attention, but there is the potential for large earthquakes on other faults in the Bay Area. There is a 62% probability of an M6.7+ in the Bay Areas in the next 30 years. The Hayward Fault has the highest probability of generating such an event (27% compared to 21% for the San Andreas). The last big earthquake along the Hayward fault was an M6.9 in 1868. The Association of Bay Area Governments offers a lot of resources about earthquakes in the Bay Area. You can look up maps of predicted ground shaking or liquefaction potential for your neighborhood for example. You can also learn what you can do to be prepared for an earthquake. Reading Putting Down Roots in Earthquake Country is also a great way to learn what you can do to protect yourself.

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