Tokyo, Japan, 27 July 2006: Researchers say they have come closer to unlocking the secrets of earthquake prediction by uncovering a link between tiny, almost imperceptible, tremors deep inside the Earth and devastating quakes capable of wiping out cities.
Key to the find are so-called silent earthquakes that move so deeply and gradually that they produce no seismic waves. But they are dangerous because they build up pressure on the upper layers of the Earth’s crust, which eventually give way to violent snaps.
A three-year joint project by the University of Tokyo and Stanford University has found a way of accurately mapping the epicenters of these minuscule pre-quakes, researcher Sho Nakamula of University of Tokyo said. The results, published earlier this month in the journal Nature, could lead to improved earthquake prediction and help save lives.
“Monitoring these silent earthquakes is important to forecasting big earthquakes later,” Nakamula said. Silent earthquakes were only recently discovered, and until now, scientists found it difficult to pinpoint their hypocenters and determine their exact triggering mechanism. The new research more accurately pinpoints those details by linking silent earthquakes to another kind of deep-earth tremor, the low-frequency earthquake, which can last as long as a couple hours.
By monitoring low-frequency quakes, scientists can more precisely determine where silent earthquakes are building up pressure and where big earthquakes are likely to erupt — with important consequences for quake-prone places like Japan or California.
Two areas studied by the researchers include the Nankai Trough off the Pacific coast of the Japanese island of Shikoku and the undersea trough off the Pacific coast of the U.S. states of Washington and Oregon. While the results shed new light on how low-frequency earthquakes can be used to predict dangerous temblors, more research is needed to determine what causes the low-frequency quakes and corresponding silent quakes to begin with, Nakamula said.