Simulations Help Plan for Large Earthquakes
LAWRENCE Livermore is one of only a few institutions with the expertise and computational resources to advance the scientific understanding of earthquakes through supercomputer simulations. These simulations have become increasingly useful for explaining the destructive forces of past earthquakes and predicting the likely consequences of future ones. To perform this work, the Laboratory combines the talents of applied mathematicians to develop numerical methods, computer scientists to develop codes, the Livermore Computing Center to run the codes on high-performance (parallel processing) computers, earth scientists to build and evaluate geologic models, seismologists to interpret results, and engineers to evaluate the response of structures to ground motion.
Simulating San Francisco Bay Area earthquakes is not a trivial task. Researchers build a grid of billions of computational nodes that are spaced about 100 meters apart to model an area 650 kilometers long by 350 kilometers wide by 50 kilometers deep. This area extends roughly from Big Sur in the south to Crescent City in the north and from the Farallon Islands in the west to the Sierra Foothills in the east. Livermore scientists begin with a model of the Bay Area’s geology developed by one of our research partners, the U.S. Geological Survey (USGS). Then they use advanced supercomputer codes developed either here or in conjunction with our colleagues at other research centers. These codes require an enormous amount of computational horsepower; one earthquake simulation used 1,024 microprocessors running together nonstop for 24 hours. The microprocessors recalculated motion at each node every 10 milliseconds.
Livermore’s high-resolution earthquake simulations, described in the article Re-creating the 1906 San Francisco Earthquake, provide the predictive capability to understand the effects of ground motion on buildings, transportation systems, and critical infrastructure. The simulations show the widespread effects of a repeat of the 1906 earthquake along the San Andreas Fault. It is important to note the consequences of environmental catastrophes that are exacerbated by increased population. The population of the greater Bay Area (19 counties) is currently about 10 times the population of 1906. If the magnitude 7.9 earthquake that occurred in 1906 were to occur today, the consequences would be devastating. A report on estimates of loss due to a repeat of the 1906 San Francisco earthquake predicts between 800 and 3,400 deaths depending on the time of day; property losses of $90 to $120 billion; 7,000 to 10,000 commercial buildings closed due to damage; and 160,000 to 250,000 households displaced. This disaster would be of similar magnitude as that of Hurricane Katrina in the Gulf Coast region, where estimated losses are between $100 and $150 billion.
According to USGS, the Hayward–Rodgers Creek Fault is the most likely source of the next large Bay Area earthquake, with a 27-percent chance of a magnitude 6.7 or greater earthquake between now and 2032. This fault has not had a major rupture since 1868. Numerous hospitals and schools are in close proximity to the Hayward–Rodgers Creek Fault. A recent study has indicated that many of these facilities need seismic strengthening. Our simulations also point to the vulnerability of the Sacramento Delta region to seismic shaking by a major earthquake occurring on one of several Bay Area fault lines. The region is protected by a network of largely unreinforced levees. Failure of these levees would threaten the quality and adequate supply of drinking water for millions of California households.
The research on the seismic faults that riddle the Bay Area, and the earthquakes they can trigger, is particularly significant to the Laboratory. Lawrence Livermore employees and their families and communities might be greatly affected by the next large Bay Area earthquake. Much of the Laboratory’s workforce crosses one or more faults during their daily commute. Our scientists have an important role to play in helping local, state, and federal authorities plan for the inevitable.