Seismologists have long relied on earthquakes or expensive tools like explosives to help create images of Earth’s interior, but a new method created by University of Colorado at Boulder researchers will produce quicker, cheaper and clearer images. Rather than waiting for earthquakes, the researchers have now recovered surface wave information from ambient seismic noise that is constantly produced by fluctuations in the Earth’s atmosphere and oceans.
Measuring surface waves is important because they help scientists get a clearer picture of the Earth’s interior, according to Michael Ritzwoller, director of CU-Boulder’s Center for Imaging the Earth’s Interior and a physics professor.
The new method promises significant improvements in the resolution and accuracy of crustal and upper mantle images down to 60 miles or more within the Earth, particularly when used in tandem with seismic projects like USArray, according to Nikolai Shapiro, a research associate in the Center for Imaging the Earth’s Interior and the study’s chief author.
In a process similar to a medical CT scan, researchers have for some years been constructing tomographic images of Earth’s crust and upper mantle from waves generated by earthquakes. This method, known as seismic tomography, reconstructs Earth’s inner structure on a computer screen, slice by slice. The new CU-Boulder method is similar, but is based on organizing ambient seismic noise, which is typically discarded as seismic garbage.
Seismic tomography is like doing a medical CT scan of the Earth, Ritzwoller said. When people have a CT scan, doctors are in control and can make images at will. Seismologists can’t control when an earthquake happens, so they can either wait, or they can set off explosives to create their own waves to generate images of the Earth’s interior. But each of these methods has drawbacks.