Scientists unveiled today results from the most comprehensive study to date of how hard and how long the ground shook in the 1906 earthquake. As a follow up, this year's 100th Anniversary Conference scheduled for April 18-22 at the Moscone Center in San Francisco will present new, comprehensive estimates of the damage such a quake would cause today based on this study.
Over a two-year period, scientists from the U.S. Geological Survey (USGS), Stanford University, Lawrence Livermore National Laboratory (LLNL), URS Corporation, and University of California at Berkeley simulated how hard and how long the ground shook as a result of the 1906 earthquake using a new three-dimensional geologic model of the San Francisco Bay area. The simulations have great potential for research, hazard loss estimation, and public education.
The 1906 simulations show how the earthquake spread from its epicenter, about two miles west of the San Francisco Zoo, and grew to cause strong shaking and damage along more than 300 miles of the San Andreas Fault. The huge geographic extent of the earthquake's impact is important for the Bay area's citizens and decision-makers to understand.
"We want to emphasize that a large earthquake such as 1906 is not just a San Francisco quake, but a Northern California earthquake," said Brad Aagaard, the USGS geophysicist who led the effort. "Earthquakes greater than magnitude 7 are going to cause intense shaking over a large area — everyone needs to be prepared."
"This remarkable study shows just how fast, how powerful, and how damaging a 1906-size earthquake would be on today's Bay Area," said Chris Poland, chairman of the 100th Anniversary Earthquake Conference. Multiple studies that examine the impact of such a quake occurring today are based on these simulations and will be among the scientific results presented at the conference, which is the science, engineering and policy centerpiece of commemoration activities.
The simulations use a three-dimensional geological and seismic velocity model, released last October by the USGS (http://quake.wr.usgs.gov/research/3Dgeologic/index.html), as well as a model for how the fault ruptured in 1906.
"For the new fault rupture model, we re-analyzed century-old surveying and seismographic data," said Seok Goo Song, a geophysics graduate student at Stanford University. "Our model confirms the rupture was about 300 miles long with a magnitude of 7.8-7.9. Our work gives new insights into the strength of strong ground shaking in large earthquakes."
The simulated ground motions were compared to ground motions reported in the famous 1908 Lawson report on the 1906 earthquake, which USGS recently mined for a new appreciation of the ground shaking in that earthquake (see http://quake.wr.usgs.gov/research/strongmotion/effects/1906/).
"These simulations give us a much more realistic and detailed picture of the strong shaking levels used for hazard loss estimation and disaster preparedness exercises and longer-term planning," said Mary Lou Zoback, a USGS seismologist and co-coordinator of the Earthquake Hazards Program in Northern California. "These easily understood simulations should increase public awareness of our hazard."
The scientists have also calculated the ground motions for the 1989 magnitude-6.9 Loma Prieta earthquake, which occurred beneath the Santa Cruz Mountains and caused damage from Watsonville to San Francisco.
"It's not that the ground motions in 1906 were significantly larger than those in 1989—it's that the area experiencing intense shaking was much, much greater," Aagaard said. "We don't know if the next rupture will look like 1906 earthquake, but we know that many of the same areas hit hard in 1906, like San Francisco, Santa Rosa, and the Santa Cruz mountains will be hit hard again in the next large earthquake on the San Andreas Fault."
"When the 1906 event reoccurs, we'd expect tremendous damage to structures around the Bay Area," said Rich Eisner, regional director of the Office of Emergency Services. "We need to rebuild now to reduce our vulnerability before an earthquake hits."
"I'm excited about the future potential of these computer models as much as anything," said Rob Graves, a seismologist at URS, an international engineering consulting firm, and project participant. "With earthquakes, we've had to learn from the past to understand or perhaps predict the future. If we can build confidence in these models ability to simulate earthquakes, we may have a way to essentially predict earthquake effects and present different earthquake scenarios.
The simulations were run on computers at the USGS, LLNL as well as Southern California Earthquake Center's facilities at the University of Southern California. LLNL scientists Shawn Larsen, Anders Petersson and Arthur Rodgers took advantage of access to the world's 45th fastest computer in running their simulations of the earthquake.
Conference representative Peggy Hellweg of the Seismological Society of America said of the animation featured in the conference video entitled QuakeMotion: "This animation and the underlying science are the culmination of recent research efforts in seismology. Such ground motion studies give us details about where the hazards are highest."
To see the 1906 and 1989 simulations, visit http://earthquake.usgs.gov/regional/nca/1906/simulations/. For other 1906 related information released by the USGS see http://earthquake.usgs.gov/regional/nca/1906/.
For a complete list of 1906 Centennial Alliance Events, exhibits, lectures and publications, see http://1906centennial.org/activities/.
The 100th Anniversary Earthquake Conference is hosted jointly by the Earthquake Engineering Research Institute, Disaster Resistant California (California's Office of Emergency Services) and the Seismological Society of America.
**** www.1906eqconf.org ****