Researchers find link between amount of silica in subduction zones and frequency

first_img Scientists have only known about slow earthquakes for a few years—since they can’t be felt, there was no real indication that they were occurring. They happen when silica rich sediment is pushed from below when one plate pushes beneath another. The fluid is trapped causing pressure to build—eventually that pressure is released by slow sliding (due to lubrication provided by the silica), rather than the jolt associated with surface quakes. After the sliding stops, the pressure begins to build up again and the whole process is repeated. Such quakes can occur over days or even weeks, releasing energy equivalent to large surface quakes. Scientists now know that such quakes occur off the coast of Japan, New Zealand, the United States and Canada, but, they all have a different frequency rate. They happen every two years in New Zealand, every six months in Japan and every 14 months beneath Canada’s Vancouver Island. The difference in rates, the researchers have found, is due to the amount of silica in the fluid—there more there is, the faster faults knit together after the sliding has stopped.The pair of researchers note that much more study needs to be done before it can be determined if slow earthquakes can be used to help predict surface quakes. In their experiments, they found the crust to be 5 to 15 percent quartz above the plates in the Cascadia subduction zone, an area that experienced a magnitude 9 quake in 1700. Scientists believe a major quake will likely occur again there sometime over the next 200 years. If slow earthquakes are found to portend larger ones, perhaps enough warning time can be given to save lives in the heavily populated area. ( —A pair of researchers, Pascal Audet and Roland Burgmann of the Universities of Ottawa and California, respectively, has found a connection between the amount of silica rich quartz above subduction zones and the frequency rate of “slow” earthquakes. In their paper published in the journal Nature, the two describe how they measured quartz amounts in the Cascadia subduction zone using seismic waves, and how it relates to slow earthquakes. Journal information: Nature Pair of seismologists publicly wonder if it might be possible to predict largest earthquakes Aerial photo of the San Andreas Fault in the Carrizo Plain, northwest of Los Angeles. Credit: Wikipedia. © 2014 Phys.orglast_img