How is an earthquake born?

Understanding how and why an earthquake is generated is one of the most fascinating and difficult questions in modern seismology. Researchers have long wondered whether, in the very first seconds of an earthquake, it is possible to tell whether it will be a mild event or a catastrophe. A new study conducted by Valeria Longobardi, Simona Colombelli and Aldo Zollo of the Department of Physics "Ettore Pancini" of the Federico II University, published in the journal Nature Communications Earth & Environment, offers an innovative answer to this conundrum.

Indeed, the research proposes a deterministic view of the origin of earthquakes: already in the first moments of the rupture of the Earth's crust, information on the magnitude and final energy of the earthquake would be found. When the earth's crust ruptures, the energy stored in the rocks is released in the form of seismic waves. However, not all earthquakes develop in the same way: some remain local and short-lived, while others propagate for hundreds of kilometers, releasing enormous amounts of destructive energy. Until now, scholars were divided between two hypotheses: the nondeterministic hypothesis, according to which all earthquakes start out the same and only then is the magnitude determined, and the deterministic hypothesis, according to which the magnitude is already defined in the first moments of the event.

To test this hypothesis, Frederick II researchers analyzed thousands of earthquakes around the world, with magnitudes between 4 and 9, using high-precision recordings from accelerometers and seismometers.
The study focused on the first few seconds of P waves, the first to be detected during an earthquake. It was found that the rate of signal amplitude growth decreases with increasing magnitude: stronger earthquakes show a slower onset but higher overall energy, while smaller ones grow faster but remain limited. This behavior has been explained through a physical model describing the propagation of rupture: in large earthquakes, the rupture velocity increases more slowly and the initial acceleration phase - called "breakout " - leaves a real physical signature in the first few seconds of the signal. This shows that each earthquake carries its own "identity" imprinted from the beginning, contradicting the idea that they all start out the same way.

In addition to its theoretical value, the research also has important practical implications. Understanding the relationship between the initial slope of the seismic signal and magnitude can improve Earthquake Early Warning Systems (EWSs), which serve to issue warnings seconds before the most destructive waves arrive. Estimating the magnitude of an earthquake in real time would enable rapid activation of safety measures, such as stopping trains, shutting down pipelines or evacuating buildings, gaining precious seconds to save lives. This study, the result of the scientific excellence of the Federico II, represents a fundamental step forward toward a deeper understanding of the physics of earthquakes and toward a society better prepared and safer in the face of earthquake risk.

Reference: Longobardi, V., Colombelli, S. & Zollo, A. The deterministic behavior of earthquake rupture beginning. Commun Earth Environ 6, 883 (2025). https://doi.org/10.1038/s43247-025-02814-z