Scientists at the Massachusetts Institute of Technology (MIT) and Stanford University have discovered a way to use ocean waves to create simulations of the motions that occurs when an earthquake is happening.
This new way of incorporating ocean waves in studying earthquakes led the scientists to discover that Los Angeles is vulnerable to a large earthquake because of its proximity to the San Andreas Fault as well as the fact that the city is on top of a sedimentary basin.
Before, ocean waves get in the way of studying earthquakes because as they hit the coast, ocean waves create seismic waves. Scientists consider these seismic waves as noise because they hinder the researchers to listen for bigger waves which might have been created by an earthquake.
However, Marine Denolle, lead author of the study from Stanford University, and her team discovered a way of using the noise to predict ground motions which an earthquake can produce. "There's a push toward using this noise and turning that into information that you would not have had otherwise," she stated. "We're using that signal in a very different way, trying to predict ground motion."
The researchers installed several seismometers along the San Andreas Fault. The seismometers were put in place in spring of 2010 and they were used to measure weak seismic waves. The seismic waves performed as proxies for the big waves that earthquakes can create and the results reflected that once the seismic waves reach the soft sediment basin beneath Los Angeles, their strength will be amplified.
This "virtual earthquake" technique is used to determine how the shaking will happen as opposed to when the earthquake will strike. This technique will show how structures within the city, especially tall buildings, will be affected by the shakings created by the earthquake.
According to geophysics professor at Stanford and senior author of the study, Greg Beroza, other cities such as Tokyo and Mexico City, which sit on top of sedimentary basins, are at risk for powerful earthquakes due to the amplified shaking. "The earthquake threat is real for Southern California," Beroza said. "Sometime in the future we'll have a big earthquake in Southern California, and these sorts of studies can help us anticipate the reach of these earthquakes and ... can motivate the public and governments to prepare for them."
The group is planning to use their virtual earthquake model in other parts of Southern California and in other cities around the world.
Results of this study were further discussed in the Jan. 24 issue of Science.
