Giant earthquakes: not as random as thought

Scientists discovered that giant earthquakes reoccur with relatively regular intervals. When also taking into account smaller earthquakes, the repeat interval becomes increasingly more irregular to a level where earthquakes happen randomly in time. In their recent paper in Earth and Planetary Science Letters , Moernaut`s team of Belgian, Chilean and Swiss researchers presented a new approach to tackle the problem of large earthquake recurrence. By analyzing sediments on the bottom of two Chilean lakes, they recognized that each strong earthquake produces underwater landslides which get preserved in the sedimentary layers accumulating on the lake floor. By sampling these layers in up to 8 m long sediment cores, they retrieved the complete earthquake history over the last 5000 years, including up to 35 great earthquakes of a magnitude larger than 7.7. "In 1960, South-Central Chile was hit by the largest known quake on earth with a magnitude of 9. Its tsunami was so massive that -in addition to inundating the Chilean coastline- it travelled across the Pacific Ocean and even killed about 200 persons in Japan," says Jasper Moernaut, an assistant professor at the University of Innsbruck, Austria, and lead author of the study.