The Hayward Fault Revealed

The Most Dangerous Urban Fault in America? AGU Sessions Indicate Hayward & Calaveras Faults Connect at Depth As the 140th anniversary of the last big earthquake on the Hayward Fault approaches, new U.S. Geological Survey studies provide mounting evidence that the Bay Area should get ready for another big quake soon. The Hayward Fault has ruptured about every 140 years for its previous five large earthquakes. October 21, 2008, marks the 140th Anniversary of the 1868 approximate Magnitude 7 earthquake. Two and half million people now live along the Hayward Fault and seven million people in the region would feel a repeat event of the same magnitude. The US Geological Survey presented new studies to partners, colleagues and media at the American Geophysical Union's annual conference in San Francisco on December 11. Scientists explained the significance of new high resolution elevation models, imagery of active deformation and creep, new results of age-dating studies, refinements and innovations to an 1868 earthquake ShakeMap, 3-D geometric and mechanical models, and ground motion simulations showing rupture along the fault. Summary of Presentations: * (S21A-0230) The October 21, 1868 Hayward Earthquake -- 140 Years Later This large earthquake caused extensive damage to the San Francisco Bay Area and remains the nations 12th most lethal earthquake, resulting in about 30 fatalities. The shaking from this earthquake was the strongest that the new towns and growing cities of the Bay Area had ever experienced, producing devastating effects on brick buildings and walls and cracking buildings as far away as Napa, Santa Rosa, and Hollister. Analysis of triangulation data suggest that the fault moved as far north as Berkeley with an average inferred slip rate of 1.9 m. The average interval between the 10 earthquakes before 1868 is 170 years, with the last five earthquakes having an average interval of only 140 years. The population at risk from a large Hayward fault earthquake is now 100 times greater than in 1868 and the infrastructure in the San Francisco Bay Area has been tested only by the relatively remote 1989 magnitude 6.9 Loma Prieta earthquake. To help focus public attention on the potential earthquake hazards, the 1868 Hayward Earthquake Alliance has been formed consisting of public and private sector agencies and corporations. The alliance is planning a series of activities leading up to the 140th anniversary on October 21, 2008 that includes public forums, conferences, commemoration events, publications, websites, videos, and public service announcements. * (S21A-0231) A Virtual Tour of the 1868 Hayward Earthquake In Google Earth The 1868 Hayward earthquake has been overshadowed by the subsequent 1906 San Francisco earthquake that destroyed much of San Francisco. Nonetheless, a modern recurrence of the 1868 earthquake would cause widespread damage to the densely populated Bay Area, particularly in the East Bay communities that have grown up virtually on top of the Hayward fault. Scientific concern has been heightened by paleoseismic studies suggesting that the recurrence interval for the past five earthquakes on the southern Hayward fault is 140-170 years. An educational Web site is being constructed using Google Earth to illustrate the cause and effect of the 1868 earthquake drawing upon scientific and historic information to visually illustrate complex scientific concepts in a way that is understandable to a non-scientific audience. The website will provide information about regional plate tectonics and faulting in western North America, to more specific information about the 1868 Hayward earthquake including models of ground shaking and historic photographs. Earthquake engineering concerns will be stressed, including population density, vulnerable infrastructure, and lifelines. Detailed maps of the Hayward fault, measurements of fault creep, and geologic evidence of an earthquake recurrence will be presented, together with the latest of valuation of seismic hazards in the San Francisco Bay region.