New paper studying the frictional behavior of fault gouges using DEM

https://doi.org/10.1029/2022JB025209

Understanding the response of a fault gouge, the granular material at the core of fault zones, can shed light on the way earthquakes are nucleated. For this purpose, in this paper, a series of particle-based simulations of a fault gouge, under conditions similar to the ones expected at deep down at the seismogenic zone, are conducted. A full scale fault with dimensions of the order of kilometers is almost impossible to be simulated at the grain-scale. In order to capture the inhomogeneities at this level, the response of several, small samples is combined in a stochastic-ensemble manner. The results suggest that local stick-slip events are vanishing with increasing number of tests thus, they are not critical for the macroscopic, global, material’s response. Contrary to this, the amount of slip needed to promote earthquake instabilities is shown to vary with respect to the mean particle size of the material. Finally, the granular polydispersity and the slip velocity do not seem to affect the system’s behavior. The later highlights possible important role of multiphysics on the rheology of fault gouges and provides evidence for the constitutive assumptions used in continuum models.

Advances in sliding mode control of earthquake instabilities via boundary tracking of wave and diffusion PDEs

Two recent results on earthquake control are summarized in this conference presentation, with emphasis on sliding mode control. A simplified model of an earthquake instability is addressed by means of a cascade system of a 1D wave equation, representing the fault slip and wave propagation, and a 1D diffusion equation, representing the injection of fluid as a diffusion process. In order to avoid a fast slip (earthquake-like behavior), the control is designed to follow a slow reference in both systems despite model uncertainties and perturbations. Simulations are additionally conducted to support the robustness and stability properties of the proposed control algorithms, by separately, obtaining critical remarks that will lead to the design of the single control for the cascade system in a future stage.

New paper on preventing seismic slip and controlling self-organized criticality

Please find enclosed a new work on earthquake and self-organized criticality control: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JB023410

Based on the mathematical developments presented in this paper and on others to follow, we show mathematically that fluid pressure can be used to stabilize and control the unstable fast seismic slip of a mature fault. In a more general framework, we discuss also the possibility of controlling complex systems exhibiting self-organized criticality due to frictional instabilities.

New paper on Thermodynamics-based Artificial Neural Networks (TANN) for the constitutive modeling of inelastic materials with microstructure

Please find enclosed the second of a series of three works on TANN that was recently published in Computer Methods in Applied Mechanics and Engineering (doi: 10.1016/j.cma.2022.115190, https://authors.elsevier.com/c/1fGS5AQEIzV-w).

In this paper we show how thermodynamics can be explicitly inserted into neural networks to guarantee thermodynamically consistent predictions of the behavior of complex materials with inelastic microstructure. We also show how internal state variables can be automatically discovered and give access to the salient micro-mechanisms that are related to the non-linear macroscopic behavior. Finally, based on a double-scale asymptotic homogenization scheme, we perform multiscale analyses achieving speed-ups of many orders of magnitude compared to micromechanical simulations.

Any comments will be highly appreciated!

Congratulations to Dr Alexandros Stathas for his successful PhD thesis defense!

I am very happy and proud of you Alexandre! Excellent work and presentation!
For those that could not attend the defense here is the full recording:
https://youtu.be/naSJC2cMEJs