When a powerful earthquake strikes, there is currently no way of knowing whether it will be followed by an even bigger one. But research by scientists at ETH Zurich could change that.
The results of a study by scientists of the Swiss Seismological Serviceexternal link at ETH Zurich raise hopes that we will soon be able to predict earthquake aftershocks in real time, says ETH Zurich in a press releaseexternal link. Such a scientific discovery “would have far-reaching consequences for civil protection, enabling more reliable decisions about evacuating people, allowing rescue workers to target their efforts accordingly, and permitting the implementation of measures to secure critical infrastructure, such as power stations”.
Based on recent seismic data, the authors of the study, recently published in Natureexternal link, have devised a method to determine whether a sequence of earthquakes is ending or will be followed by an even more powerful earthquake. The relevant parameter they looked at was the so-called “b-value”, which characterises the relationship between the magnitude and number of quakes. Laboratory measurements show that this value indirectly indicates the state of stress in the Earth's crust.
The researchers demonstrated that the b-value changes systematically in the course of an earthquake sequence. To prove this, they examined data from 58 sequences and came up with a traffic-light system (red for acute danger, green for all-clear) indicating what would happen next. The traffic-light system devised by the researchers turned out to be accurate in 95 percent of the cases they examined.
Whereas most major earthquakes are not preceded by foreshocks, they are always followed by thousands of aftershocks, whose frequency and magnitude fade over time, explains ETH Zurich. But sometimes a major earthquake is followed by an even bigger one. This was what happened in the sequences of earthquakes that hit Central Italy in 2016 or Ridgecrest, California in the US in July 2019.