Researchers from Germany, USA and Chile analyzed two earthquakes among the largest in the history of mankind and found that they were both preceded by a strange change of direction of the Earth’s surface . On their findings, the team said in an article published in the journal Nature.
Using modern geophysical methods of research, a team of scientists found a huge thousand kilometer region of the earth’s surface near the boundary of one of the tectonic plates, the movement of which could lead to two large earthquakes in Chile in 2010 (magnitude 8.8) and in Japan in 2011 (magnitude of 9.0), which caused a devastating tsunami and the accident at the Fukushima nuclear power plant.
Both events occurred on the Pacific coast, where oceanic plates dive under the continental crust in the subduction process. In Japan, there is a large network of geodetic stations, which allow using a satellite navigation system (GNSS) to track how fast and in what direction the Earth moves. In Chile, this network is not as extensive, but in this country, the experts track the movement of the deforming continental plate.
Typically, stations on land are permanently removed from the trough subduction because continental crust is compressed. However, studying the time series of signals from the satellite stations, the researchers found that the change in direction: suddenly it turned out that that station has moved in the direction of the depressions of subduction, i.e. towards the open ocean at four to eight millimeters. Then, the direction returned to normal. Very soon after the second turn and there was a powerful earthquake.
Using simple geological model, the authors were able to assume that these changes of direction occur in periods when there are rapid changes in the oceanic plate as subduction. Accordingly, the researchers suggest that these periods have sped up the inevitable failure of the smaller parts of the subduction zone. Whether such a strong change of direction to happen before the next big earthquake, scientists have yet to learn, but from this study it is clear that the subduction zone is much more dynamic in the observed time scale than previously thought.
“We originally thought that the deeper subduction occurs with a fairly constant velocity between large earthquakes. But now it turned out that we understood this process in a highly simplified form. In fact, the change in the velocity of subduction can be a key factor in understanding how the emerging major earthquake,” concludes the study’s lead author, fellow of the Potsdam centre of the Helmholtz Jonathan Bedford.
