Properties of FAULTS, a key to Realistic Generic Earthquake Modeling and hazard Simulation – FAULTS_R_GEMS

The first part of the work aimed to characterize the two major properties of the faults targeted in the project: structural maturity and tectonic damage. The goal was to identify one or more ways to measure these properties using basic data—whether derived from the scientific literature or acquired from Earth imagery or field observations.

A second part of the work involved examining how these properties are related. The goal was to determine whether empirical relationships exist between the various fault parameters, particularly over the course of their geological evolution.

A third part of the work involved comparing the properties of the faults with certain aspects of strong earthquakes generated on faults whose degree of maturity or damage is known or assumed. The aim was to examine whether empirical relationships exist between fault properties and earthquake properties (particularly the amplitudes of surface displacements and the intensity of ground accelerations).

Finally, the last part aimed to incorporate the established relationships—or testing the empirical relationships—into theoretical rupture models and theoretical earthquake early warning protocols.

Maturity measures the duration of a fault’s activity: the longer a fault has been generating earthquakes (generally, thousands to millions of years), the more mature it is. We have demonstrated that a fault’s degree of maturity can be measured either through a combination of four basic fault parameters—age of initiation, cumulative displacement, length, and slip rate (Manighetti et al., in review, 2026)—or by the degree of undulation and continuity of its surface trace (Manighetti et al., 2021). We have developed and released a code that enables the automatic measurement of cumulative displacements along vertical-slip faults (Giampietro et al., 2025).

Tectonic damage is a deformation—primarily brittle (i.e., via fractures and secondary faults)—that occurs around the parent fault as it undergoes repeated seismic ruptures. We have acquired large quantities of optical imagery of the Earth (satellite, drone, and ground-based) documenting damage around a large number of faults of varying lengths, slip modes, and contexts. We have developed a code to identify and measure the damage in these images (Giampietro et al., in preparation). The damage data are still under analysis, to determine scaling relations describing how damage zones grow as faults become more mature.

We have built the largest currently available database presenting the distributions of displacement generated at depth by 163 strong historical earthquakes, as determined in more than 1,000 “source models.” The database also presents, in parallel, the maturity properties of the faults ruptured by the 163 earthquakes. Our joint analysis of these earthquakes and faults demonstrates that the degree of fault maturity modulates the amount of displacement produced at the surface by an earthquake. However, it is primarily the earthquake’s magnitude and the depth of its peak displacement that most strongly control the amplitude of the slip fraction that reaches the ground surface and produces damages (Manighetti et al., 2026, in review).

We have developed theoretical rupture models demonstrating that damage around faults contributes to increased seismic displacements and ground acceleration intensity (Oral et al., 2020; Flores-Cuba et al., 2024).

We have incorporated some of the established empirical laws into an experimental earthquake early warning protocol. The results are encouraging, as they demonstrate that taking into account the degree of maturity of the fault during rupture allows for faster prediction of the magnitude of the ongoing earthquake, as well as the amplitude and distribution of the displacements that this earthquake will ultimately produce at the surface (Hutchison et al., 2020; Böse et al., 2021).

The COVID-19 crisis and a few other challenges have slowed down the project, so we have not yet finalized certain aspects, particularly the modeling component. One initial avenue of research is therefore to continue working on incorporating established empirical fault-earthquake relationships—or testing them—into physical rupture models.

The earthquake-fault database we have built opens up the possibility of analyzing more relationships than we had initially imagined. A second approach is therefore to take full advantage of this rich database.

Manually mapping parent faults and the fractures/faults within their damage zones is an extremely time-consuming and difficult task. One approach is to attempt to automate this process by developing an algorithm based on artificial intelligence. During the project, we tested this approach with encouraging results (Mattéo et al., 2021). We are now poised to take this project a step further. If successful, we will have access to an unparalleled amount of fault and damage zone maps, which will allow us to more strongly constrain the empirical relationships we have begun to establish in this project.

Ultimately, we hope that the fault-earthquake relationships established in this project and its follow-up will help strengthen the predictive capabilities of rupture models: while it is not currently possible to predict the exact date of an earthquake, it is becoming possible to anticipate its nucleation zone, its potential extent and thus its magnitude, the amplitude of the resulting displacements—particularly at the surface—and the intensity of ground accelerations. These factors are crucial for assessing seismic hazard and risk, and thus for protecting the public.

Decades of research on earthquakes have yielded meager prospects for earthquake predictability: we cannot predict the time, location and magnitude of a forthcoming earthquake with sufficient accuracy for immediate societal value. Therefore, the best we can do is to mitigate their impact by anticipating the most “destructive properties” of the largest earthquakes to come: longest extent of rupture zones, largest magnitudes, amplitudes of displacements, accelerations of the ground. This topic has motivated many studies in last decades. Yet, despite these efforts, major discrepancies still remain between available model outputs and natural earthquake behaviors. Here we argue that an important source of discrepancy is related to the incomplete integration of actual geometrical and mechanical properties of earthquake causative faults in existing rupture models.
Indeed, our group has been among the pioneers to show that faults are 3D features, systematically embedded in a permanent damage zone where crustal rocks are intensely faulted and hence are compliant. Faults also are systematically segmented laterally in a generic manner, and this segmentation divides their planes and produces strength and stress heterogeneities in a deterministic manner. As faults grow over the long-term and become more “mature”, some of their properties evolve: the damage zone enlarges and its compliance increases, the fault segments become more tightly connected, the fault plane roughness decreases as might also do the fault friction. All these fault properties and their changes in relation to fault maturity markedly modify the earthquake behavior. In particular, earthquakes on mature and immature faults produce different amplitudes of slips and ground motions, whereas earthquake slips and speeds are systematically largest on the most mature sections of the ruptured zones.
These intimate connections between fault and earthquake properties mean that a synoptic understanding of earthquake mechanics cannot be successful until it more fully includes actual fault properties. This is not done at present, as most current earthquake models either ignore fault properties or oversimplify them. We thus aim to take benefit of the fault data and knowledge we have gained in the last decades, and of our strong experience in earthquake modeling, to develop a new generation of rupture and ground motion (GM) models, based on a novel paradigm: 3D fault zones with generic macroscopic properties (especially permanent damage and lateral segmentation) whose inhomogeneous and anisotropic characters evolve depending on both overall and along-strike fault maturity. Furthermore, since most major fault properties are deterministic, even generic, they must result from some common, scale-invariant physics. The understanding of that physics should advance generic earthquake and GM models that could be run for the vast majority of faults and earthquakes worldwide. These new models should thus open a novel avenue in earthquake modeling.
We first aim to document the compliance of rocks in natural permanent damage zones. These data –key to earthquake modeling– are presently lacking. A second objective is to introduce the observed macroscopic fault properties –compliant permanent damage, segmentation, maturity– into 3D dynamic earthquake models we have developed in prior works. A third objective is to compute Ground Motions (GM) from these new fault-based earthquake models and propagate them into non-linear media, using codes that we have developed. A fourth objective is to conduct a pilot study aiming at examining the gain of prior fault property and rupture scenario knowledge for Earthquake Early Warning (EEW).
We expect that integrating actual fault properties in dynamic rupture, GM, and EEW models will decrease the discrepancies between models outputs and natural earthquake behavior, and hence allow a more accurate anticipation of the “destructive properties” of forthcoming events.