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DisastersWhy some quakes lead to faster shaking

Published 1 November 2012

The more time it takes for an earthquake fault to heal, the faster the shake it will produce when it finally ruptures, according to a new study; the research does nothing to bring scientists closer to predicting when the next big one will hit, but the findings could help engineers better assess the vulnerabilities of buildings, bridges, and other structures when a fault does rupture

The more time it takes for an earthquake fault to heal, the faster the shake it will produce when it finally ruptures, according to a new study by engineers at the University of California, Berkeley, who conducted their work using a tabletop model of a quake fault.

“The high frequency waves of an earthquake — the kind that produces the rapid jolts — are not well understood because they are more difficult to measure and more difficult to model,” said study lead author Gregory McLaskey, a former UC Berkeley Ph.D. student in civil and environmental engineering. “But those high frequency waves are what matter most when it comes to bringing down buildings, roads and bridges, so it’s important for us to understand them.”

A University of California, Berkeley release reports that while the study, to be published today, 1 November, in Nature and funded by the National Science Foundation, does nothing to bring scientists closer to predicting when the next big one will hit, the findings could help engineers better assess the vulnerabilities of buildings, bridges, and other structures when a fault does rupture.

“The experiment in our lab allows us to consider how long a fault has healed and more accurately predict the type of shaking that would occur when it ruptures,” said Steven Glaser, UC Berkeley professor of civil and environmental engineering and principal investigator of the study. “That’s important in improving building designs and developing plans to mitigate for possible damage.”

To create a fault model, the researchers placed a Plexiglas slider block against a larger base plate and equipped the system with sensors. The design allowed the researchers to isolate the physical and mechanical factors, such as friction, that influence how the ground will shake when a fault ruptures.

It would be impossible to do such a detailed study on faults that lie several miles below the surface of the ground, the authors said. Current instruments are generally unable to accurately measure waves at frequencies higher than approximately 100 Hertz because they get absorbed by the earth.

“There are many people studying the properties of friction in the lab, and there are many others studying the ground motion of earthquakes in the field by measuring the waves generated when a fault ruptures,” said McLaskey. “What this study does for the first time is link those two phenomena. It’s the first clear comparison between real earthquakes and lab quakes.”

Noting that fault surfaces are

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