The dynamics of earthquakes are better understood thanks to three-dimensional modeling of fault sliding.
In an article published on November 9 in the journal Nature Geoscience, Jean-Paul Ampuero and Huihui Weng, from Université Côte d’Azur and IRD, propose a new model to predict the propagation speed of earthquakes.
Among the most damaging natural hazards, earthquakes remain one of the least understood phenomena in the Earth sciences.
The slip of a fault
Earthquakes occur when a tectonic fault slides. However, the slip does not occur over the entire fault at the same time, but starts at a point, called the hypocenter, and then spreads over the fault.
The speed at which the slip spreads is called the “rupture velocity” of the earthquake. Geophysicists are particularly interested in this parameter: indeed, the faster this speed is, the stronger the seismic waves are and the most significant damages it causes.
The seismic models built so far have concluded that earthquakes cannot propagate in a stable and sustained manner at arbitrary velocities, but that there is a range of “forbidden velocities” between the velocities of the P and S waves, the two main seismic waves propagating in the Earth. However, advances in seismological observation of earthquakes have shown that recent earthquakes have indeed propagated at forbidden velocities.
This is the case, for example, of the 2018 earthquake in Palu, Indonesia, which caused a destructive tsunami.
To solve this dilemma, researchers at Université Côte d’Azur and IRD have built a new model to predict the velocity of earthquake propagation. They relied on the computer of the Observatoire de la Côte d’Azur, which is part of OPAL, a shared platform that brings together the region’s large high-performance scientific computers.
They focused on overcoming two crucial limitations of the previous models. The first: the models only predicted two dimensions, whereas the Earth has three dimensions.
The second: the direction of sliding is not always horizontal or vertical, but can be oblique. By overcoming these two limitations, the researchers were able to explain why these propagation speeds are not prohibited, but possible.
“A major challenge in earthquake prevention is to predict the impacts of earthquakes. Introducing more physics into the evaluation of seismic hazard, which is very empirical, is an opportunity we must seize,” stresses H. Weng.
“The proposed new model provides validated theoretical elements that could, in the long term, enrich the way seismic risk is assessed,” adds J.-P. Ampuero.
From a press release by IRD.