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Pierre Romanet

Publications and source records attributed to Pierre Romanet.

7 recordsLinked to original sources
arXiv2026

A divide-and-conquer strategy for fast elastodynamic simulation of earthquakes and aseismic slip on fault networks

Simulating long-term, fully dynamic sequences of earthquakes and aseismic slip (SEAS) on geometrically complex fault networks remains computationally demanding due to the cost of resolving elastodynamic interactions. Although high-performance computing improves feasibility, simulations remain expensive, particularly for multicycle evolution, motivating the widespread use of quasi-dynamic approximations based on radiation damping. Here we present an efficient numerical framework for fully elastodynamic SEAS simulations on complex fault networks. The method adopts a divide-and-conquer strategy in which elastodynamic self-effects and fault-to-fault interactions are treated separately using boundary integral formulations tailored to each interaction type. Self-interactions along planar faults are computed using a non-replicating spectral boundary integral formulation that eliminates periodic-image artifacts, while interactions between arbitrarily oriented faults are evaluated through a fully dynamic space-time boundary integral representation accelerated by hierarchical matrices (H-matrices). A key advance is a selective H-matrix compression strategy based on fault-wise assembly of independent binary trees, enabling low-rank approximation of long-range interactions while preserving near-field accuracy and excluding self-effects from the hierarchical structure. Additional efficiency arises from physics-informed truncation of elastodynamic histories using mode-dependent time windows and causality-based kernel truncation. Benchmark multi-fault simulations validate accuracy against reference uncompressed solutions. The method reduces interaction complexity from O(N^3) to O(N^2 log N), yielding up to three orders of magnitude speedup and an order-of-magnitude memory reduction for typical problem sizes (~3e10 degrees of freedom), enabling fully dynamic SEAS simulations on workstation hardware.

physics.geo-ph↗
arXiv2025

A rate-and-state friction based criterion for the probability of earthquake fault jumps

Geometrical complexities in natural fault zones, such as steps and gaps, pose a challenge in seismic hazard studies as they can act as obstacles to seismic ruptures. In this study, we propose a criterion, which is based on the rate-and-state equation, to estimate the efficiency of an earthquake rupture to jump between two spatially disconnected faults. The proposed jump criterion is tested using a 2D quasi-dynamic numerical simulations of the seismic cycle. The criterion successfully predicts fault jumps where the simpler Coulomb stress change calculation fails to do so. The criterion includes the Coulomb stress change as a parameter but is also dependent on other important parameters among which is the absolute normal stress on the fault the rupture jumps to. Based on the criterion, the maximum jump distance increases with decreasing absolute normal stress, i.e. as the rupture process occurs closer to the Earth's surface or as pore pressure increases. The criterion implies that earthquakes can jump to arbitrary large distances at the Earth's surface if the normal stress is allowed to go to zero, underscoring the potential for large jump distances (i.e. >5 km). We further propose a probabilistic framework to estimate the likelihood of rupture jumps by accounting for uncertainties in fault geometry and earthquake source parameters. Additionally to its role into seismic hazard assessment, this criterion could complement Coulomb stress change maps with those of triggered slip-rates on receiver faults due to quasi-instantaneous stress perturbations, as well as estimates of jump probabilities accounting for parameter uncertainties.

physics.geo-ph↗
arXiv2024

Coupled Boundary Element and Finite Volume Methods for Modeling Fluid-Induced Seismicity in Fault Networks within Low-Permeability Rocks

To better understand the mechanics of injection-induced seismicity, we developed a two-dimensional numerical code to simulate both seismic and aseismic slip on non-planar faults and fault networks driven by fluid diffusion along permeable faults. Our approach integrates a boundary element method to model fault slip governed by rate-and-state friction with a finite volume method for simulating fluid diffusion along fault networks. We demonstrate the method's capabilities with two illustrative examples: (1) fluid injection inducing slow slip on a primary rough, rate-strengthening fault, which subsequently triggers microseismicity on secondary, smaller faults, and (2) fluid injection on a single fault in a network of intersecting faults, leading to fluid diffusion and reactivation of slip throughout the network. In both cases, the simulated slow slip migrates more rapidly than the fluid pressure diffusion front. The observed migration patterns of microseismicity in the first example and slow slip in the second example resemble diffusion processes but involve diffusivity values that differ significantly from the fault hydraulic diffusivity. These results support the conclusion that the microseismicity front is not a direct proxy for the fluid diffusion front and cannot be used to directly infer hydraulic diffusivity, consistently with some decametric scale in-situ experiments of fault activation under controlled conditions. This work highlights the importance of distinguishing between mechanical and hydrological processes in the analysis of induced seismicity, providing a powerful tool for improving our understanding of fault behavior in response to fluid injection, in particular when a network of faults is involved.

physics.geo-ph↗
arXiv2021

Fully dynamic earthquake cycle simulations on a non-planar fault using the spectral boundary integral element method

One of the most suitable methods for modeling fully dynamic earthquake cycle simulations is the spectral boundary integral element method (sBIEM), which takes advantage of the fast Fourier transform (FFT) to make a complex numerical dynamic rupture tractable. However, this method has the serious drawback of requiring a flat fault geometry due to the FFT approach. Here we present an analytical formulation that extends the sBIEM to a mildly non-planar fault. We start from a regularized boundary element method and apply a small-slope approximation of the fault geometry. Making this assumption, it is possible to show that the main effect of non-planar fault geometry is to change the normal traction along the fault, which is controlled by the local curvature along the fault. We then convert this space--time boundary integral equation of the normal traction into a spectral-time formulation and incorporate this change in normal traction into the existing sBIEM methodology. This approach allows us to model fully dynamic seismic cycle simulations on non-planar faults in a particularly efficient way. We then test this method against a regular boundary integral element method for both rough-fault and seamount fault geometries, and demonstrate that this sBIEM maintains the scaling between the fault geometry and slip distribution.

physics.geo-ph↗
arXiv2019

Paradox of Modeling Curved Faults Revisited with General Non-Hypersingular Stress Green's Functions

In a dislocation problem, a paradoxical discordance is known to occur between an original smooth curve and an infinitesimally discretized curve. To solve this paradox, we have investigated a non-hypersingular expression for the integral kernel (called the stress Green's function) which describes the stress field caused by the displacement discontinuity. We first develop a compact alternative expression of the non-hypersingular stress Green's function for general two- and three-dimensional infinite homogeneous elastic media. We next compute the stress Green's functions on a curved fault and revisit the paradox. We find that previously obtained non-hypersingular stress Green's functions are incorrect for curved faults, and that smooth and infinitesimally segmented faults are equivalent. Their compatibility bridges the gap between analytical methods featuring curved faults and numerical methods using subdivided flat patches.

physics.geo-ph↗
arXiv2017

Fast and slow earthquakes emerge due to fault geometrical complexity

Active faults release elastic strain energy via a whole continuum of modes of slip, ranging from devastating earthquakes to Slow Slip Events and persistent creep. Understanding the mechanisms controlling the occurrence of rapid, dynamic slip radiating seismic waves (i.e. earthquakes) or slow, silent slip (i.e. SSEs) is a fundamental point in the estimation of seismic hazard along subduction zones. On top of showing slower rupture propagation velocity than earthquakes, SSEs exhibit different scaling relationships, which could reflect either different physical mechanisms or an intriguing lack of observations. Like earthquakes, SSEs are bound to occur along unstable portions of active faults, raising the question of the physical control of the mode of slip (seismic or aseismic) along these sections. Here, we use the numerical implementation of a simple rate-weakening fault model to explain the spontaneous occurrence, the characteristics and the scaling relationship of SSEs and earthquakes. We show that the simplest of fault geometrical complexities with uniform friction properties can reproduce slow and fast earthquakes without appealing to complex rheologies or mechanisms. Our model helps resolve many of the existing paradoxes between observations and physical models of earthquakes and SSEs.

physics.geo-ph↗