Seismological and geodetic observations of fault zones reveal diverse slip dynamics, scaling, and statistical laws. Existing mechanisms explain some but not all of these behaviors. We show that incorporating an off\u2010fault damage zone—characterized by distributed fractures surrounding a main fault—can reproduce many key features observed in seismic and geodetic data. We model a 2D shear fault zone in which off\u2010fault cracks follow power\u2010law size and density distributions, and are oriented either optimally or parallel to the main fault. All fractures follow rate\u2010and\u2010state friction with parameters enabling slip instabilities. We do not introduce spatial heterogeneities in frictional properties. Using quasi\u2010dynamic boundary integral simulations accelerated by hierarchical matrices, we simulate slip dynamics and analyze events produced both on and off the main fault. Despite spatially uniform frictional properties, we observe a natural continuum from slow to fast ruptures, as seen in nature. Our simulations reproduce the Omori law, inverse Omori law, Gutenberg\u2010Richter scaling, and moment\u2010duration scaling. We observe seismicity localizing toward the main fault before nucleation of main\u2010fault events. During slow slip events (SSEs), off\u2010fault seismicity migrates in patterns resembling fluid diffusion fronts, despite the absence of fluids. We show that tremors, very low\u2010frequency earthquakes, low frequency earthquakes, SSEs, and earthquakes can all emerge naturally within this fault volume framework, making it an ideal digital twin for testing hypotheses, performing ground\u2010truth inversions, and probing mechanical properties inaccessible with natural observations.
", "doi": "10.1029/2025jb032915", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research: Solid Earth", "publication_date": "2026-05", "series_number": "5", "volume": "131", "issue": "5", "pages": "e2025JB032915" }, { "id": "authors:ry91c-epq72", "collection": "authors", "collection_id": "ry91c-epq72", "cite_using_url": "https://authors.library.caltech.edu/records/ry91c-epq72", "type": "article", "title": "A Rate-and-State Friction Based Criterion for the Probability of Earthquake Fault Jumps", "author": [ { "family_name": "Michel", "given_name": "Sylvain", "orcid": "0000-0001-7878-6603" }, { "family_name": "Scotti", "given_name": "Oona" }, { "family_name": "Hok", "given_name": "Sebastien", "orcid": "0000-0003-1341-8476" }, { "family_name": "Bhat", "given_name": "Harsha S.", "orcid": "0000-0003-0361-1854", "clpid": "Bhat-Harsha-Suresh" }, { "family_name": "Kheirdast", "given_name": "Navid", "orcid": "0000-0003-2453-6136" }, { "family_name": "Romanet", "given_name": "Pierre", "orcid": "0000-0001-6232-4906" }, { "family_name": "Almakari", "given_name": "Michelle", "orcid": "0000-0002-4041-8028" }, { "family_name": "Cheng", "given_name": "Jinhui", "orcid": "0000-0001-7083-4412", "clpid": "Cheng-Jinhui" } ], "abstract": "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\u2010and\u2010state 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\u2010dynamic 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, that is, 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\u2010rates on receiver faults due to quasi\u2010instantaneous stress perturbations, as well as estimates of jump probabilities accounting for parameter uncertainties.
", "doi": "10.1029/2025jb031449", "issn": "2169-9313", "publisher": "American Geophysical Union", "publication": "Journal of Geophysical Research: Solid Earth", "publication_date": "2026-04", "series_number": "4", "volume": "131", "issue": "4", "pages": "e2025JB031449" } ]