Big one or small one? Scientists learn more about predicting earthquakes

Is it possible to predict earthquakes? Scientists are reportedly closer than ever to the answer. Scientists have collected seismic data from more than 1000 sites and it shows a connection between the strength of faults and the size of earthquakes. The data hints at the likelihood of forecasting how close an area is to facing a major seismic event.

Japan sits on the Pacific Ring of Fire and is highly earthquake-prone. It witnesses a whopping 100,000 minor tremors annually and is also at risk of being hit with a major one. Japanese scientists are trying to study the smaller tremors to understand the processes within the Earth’s crust that trigger a major earthquake.

Researchers from Kyushu University and the University of Tokyo, Japan, studied the seismic activity in great detail and have identified a link between fault strength and the magnitude of an earthquake.

The study has been published in Nature Communications. The researchers propose that the strength of the fault affects the b-value, and consequently the chances of a major earthquake.

Professor Satoshi Matsumoto, the first author of the study, explains, “The b-value is a very important constant in seismology that characterizes the relationship between earthquake frequency and size."

A lower b-value indicates that there is a higher chance of bigger earthquakes.

“If there is a low b-value, this means there is a higher proportion of large earthquakes, while a high b-value means there is a higher proportion of smaller earthquakes.”

The b-value differs from location to location and changes over time. It often decreases right before a major earthquake.

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The latest study brings the strength of the fault into the picture and says that it also plays a role.

Studying theWestern Tottori Earthquake

The study looked at the epicentre of the Western Tottori Earthquake of magnitude 7.3 which occurred in 2000. The region still witnesses seismic action and the researchers installed more than 1000 seismic stations to accurately make observations.

“Under certain stress conditions on each tectonic regime, there is a favourable direction of the fault plane to slip. When faults are in unfavourable directions, this suggests that these are weak faults that can slip more easily. On the other hand, strong faults require more stress to slip, and have a much more characteristic direction,” explains Matsumoto.

“Simply put, these weak faults will likely slip before a large amount of stress builds up, which means that they aren’t able to release a large amount of force,” says Matsumoto.

While the researchers admit that it might never be possible to predict an earthquake, the latest observations might help them move closer to the “holy grail” of forecasting major tremors.

"Data such as fault direction and fault strength, and calculating b-values, could help us estimate when a fault has reached a critical point,” Matsumoto said. “This information is vital to know in order to be prepared for major earthquakes.”