Over at NICS, Scott Gibson writes that recent simulations on the Kraken supercomputer show a way to improve earthquake planning scenarios.
Our recent work accounts for the limited strength of crustal rocks; that is, we simulate the absorption of rupture energy by permanent rock deformation,” said Daniel Roten of the Swiss Seismological Service. “Our results suggest that this nonlinear behavior in rocks could reduce the previous simulation-based estimates of expected ground motion velocity [the speed at which the ground would shift] in the Los Angeles basin during a magnitude-7.8 event on the southern San Andreas Fault by 30 to 70 percent.”
According to Roten, nonlinear material response occurs in soft soils near the surface, lessening high-frequency (>1 Hz) shaking that controls damage to low- and mid-rise buildings. The existence of such behavior is well established in earthquake research, he says, adding that this type of nonlinearity is routinely treated in engineering seismology equations, and was provided for in the original ShakeOut Earthquake Scenario—but until the recent research performed with Kraken, it was not factored into computer simulations.
Our simulations show that nonlinear response in crustal rocks may also reduce the amplitudes of long-period surface waves that pose a hazard to high-rise buildings, meaning the degree of destruction would be less than anticipated,” Roten says. These reductions, he explains, could be important because the collapse of high-rise structures represents a substantial aspect in the damage and casualty estimates of the ShakeOut Earthquake Scenario.
Roten points out that more research will be needed to quantify the impact of these findings on damage and casualty estimates for future magnitude-7.8 earthquakes on the San Andreas Fault.
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