“Predicting” Earthquakes with GPS Station Networks: Two Innovative Studies from Our University

Can earthquakes be “predicted”? Can we identify and recognize signals that can reasonably be considered “warnings”? These questions, among the most relevant and recurring in the seismological field, have motivated two studies led by the University of Parma, recently published in the “Journal of Geophysical Research: Solid Earth” and in “Scientific Reports”, and focused on two of the most significant earthquakes of the beginning of the millennium: the 2009 L’Aquila earthquake (magnitude 6.3) and the 2008 Sichuan earthquake (magnitude 7.9).

The first author of both is Giampiero Iaffaldano, professor of Solid Earth Geophysics at the Earth Sciences Unit at the Department of Chemical, Life and Environmental Sustainability Sciences of the University of Parma. The first study is entitled Variations of Whole–Adria Microplate Motion During the Interseismic Phase Preceding the MW 6.3, 6 April 2009 L’Aquila (Italy) Earthquake, and was published in June in the «Journal of Geophysical Research: Solid Earth». The second, entitled Impact of the 2008 MW 7.9 Great Wenchuan earthquake on South China microplate motion, was published in July in «Scientific Reports». Their novelty lies mainly in demonstrating that there are signals associated with earthquakes that can be detected by GPS (the same system used on maps and smartphone navigators) much earlier and far away, and that therefore they could potentially be exploited to mitigate seismic risk. As is well known, the Earth’s surface is divided into a mosaic of tectonic plates that move in different directions at speeds ranging from a few millimeters to centimeters per year. The motions between plates in contact with each other generate a slow accumulation of energy, which is then suddenly released through earthquakes. The L’Aquila earthquake, for example, released energy accumulated over time along part of the Apennines due to the motion between the Adria plate (which includes central and northern Italy) and the African plate. It is well established in the scientific community that motions between plates fuel the genesis of earthquakes. However, the community has always assumed that the opposite was not true, that is, that earthquakes and their slow preparatory phase of energy accumulation (which, together, are called seismic cycles) had no effect on the motions of the plates. Very recent studies, including the two just published, demonstrate that earthquakes do have a tangible and measurable effect on the motions of entire plates. These effects are evident from GPS measurements even several years before the earthquake occurs. The article on the L’Aquila earthquake shows that there was a 20% slowdown in the motion of the Adria plate in the 6 years preceding the 2009 earthquake. “I think the scientific interest of this discovery – explains Giampiero Iaffaldano – is that it opens a new perspective, never considered before, on the mitigation of seismic risk. To put it in a nutshell, we usually look for precursor signals in the months or days preceding large earthquakes, and in the immediate vicinity of notoriously active faults. These studies demonstrate that the seismic cycle (the slow accumulation of energy followed by the earthquake) is able to modify the motion of entire tectonic plates, which is measured over the years through networks of GPS stations located hundreds or even thousands of kilometers away from what will later be the epicenter. This implies that there are potentially precursor signals even years before and at great distances from large earthquakes. The prospect of exploiting these signals in seismic risk assessments is something absolutely new.”