New Study Reveals Hidden Complexity of Small Earthquakes
Not all earthquakes make the news, but even the small ones can reveal big secrets about what is happening beneath our feet. In a new study published in Nature Communications, researchers from the Faculty of Mathematics and Physics at Charles University and Italy’s National Institute of Geophysics and Volcanology (INGV) present a new method to study weak earthquakes, offering a window into the fine-scale physical processes that govern tectonic ruptures.
Small earthquakes occur frequently worldwide and are recorded by dense seismic networks, yet their detailed rupture dynamics have long been difficult to study. The research team, led by František Gallovič from Charles University, used advanced physics-based numerical simulations to interpret a unique observational dataset developed and provided by INGV Milan.
The approach was demonstrated on two moderate (magnitude ~4) earthquakes in Central Italy. The findings suggest that variations in stress and frictional properties follow a fractal pattern, indicating that physical complexity persists down to the smallest scales resolvable from the data.
Figure: Example of observed data (spectral amplitudes at ~100 seismic stations, marked by triangles) used to estimate stress and frictional parameters of two selected earthquakes in Central Italy. Interestingly, the smaller event (left) shows strong directivity towards the southeast, which is reflected in the inferred model of the rupture propagation (see Video).
“Until now, the physics of small earthquakes has been largely hidden,” said František Gallovič. “We now have evidence that even weak earthquakes can be governed by the same physical complexity as large ones.”
The research highlights how even weak earthquakes can help scientists piece together the physics behind tectonic faulting. These insights can help refine physical models of earthquakes and, in the long run, improve the seismic hazard assessment.
Video: Resulting complex rupture propagation of the two studied earthquakes in Central Italy using a physics-based friction model. For each event, the model represents one of many solutions that agree with the observed spectra statistically.
Publication:
Physics-based broadband characterization of
weak earthquakes, by František Gallovič, Sara Sgobba, and Ľubica
Valentová Krišková, published in Nature Communications (2025) 16:
11300. DOI: https://doi.org/10.1038/s41467-025-66461-w
