Quakefinder Blog

108 year anniversary of the 1906 San Francisco Earthquake

At 5:12 AM on April 18, 1906, the ground shook like it had never done before in San Francisco. An estimated Magnitude 7.8 earthquake broke the city, and started numerous fires that decimated what was left of many structures. Over 3,000 people died. This major earthquake ruptured 296 miles (477 kilometers) of the San Andreas Fault from San Juan Bautista to Cape Mendocino. No warning was available then. Even today, 108 years later, there is no accepted warning system for such a quake. In 1906, horses were reported to be agitated in the barns near the Presidio prior to the quake. What were they sensing? We think that they may have sensed ultra low frequency magnetic waves or static electricity from ionized air around them. Today we have instrumented much of the San Andreas and other major faults in California with sensitive magnetometers and air ionization sensors to see if these phenomena occur regularly before large quakes. We are actively collecting a valuable “baseline” of electromagnetic signatures for these faults. The hope is that future major quakes repeat the same two week sequence of magnetic pulses and air conductivity changes observed by QuakeFinder instruments that preceded the M5.4 Alum Rock, CA and M6.2 Tacna, Peru quakes in 2007 and 2010 respectively.

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