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- Lei, Qinghua, et al.
(author)
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A Stochastic Dynamical Model of Slope Creep and Failure
- 2023
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 50:11
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Journal article (peer-reviewed)abstract
- We propose a stochastic dynamical model to simulate slope secondary and tertiary creep phenomena. The slope secondary creep is represented by the Kesten process defined as a stochastic affine auto-regressive process involving both multiplicative and additive random variables. The Kesten process can realistically capture the co-existence of a background deformation and intermittent displacement bursts, which are together well characterized by an inverse gamma velocity distribution. The slope tertiary creep is modeled by a nonlinear stochastic dynamical equation embodying a nonlinear feedback mechanism and a nonlinear random effect, which can mimic the development of slow or catastrophic landslides. For catastrophic landslides, the probability density function of slope velocities tends to deviate from the inverse gamma distribution by populating the "dragon-king" regime, although sometimes they may grow undetectably in the "black-swan" regime. Our model provides a quantitative framework to understand, simulate, and interpret complex landslide displacement time series.
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- Lei, Qinghua, et al.
(author)
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Anderson localisation and reentrant delocalisation of tensorial elastic waves in two-dimensional fractured media
- 2021
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In: Europhysics letters. - : Institute of Physics Publishing (IOPP). - 0295-5075 .- 1286-4854. ; 136:3
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Journal article (peer-reviewed)abstract
- We study tensorial elastic wave transport in two-dimensional densely fractured media using numerical simulations and document transitions from propagation to diffusion and to localisation/delocalisation. For large fracture stiffness, waves are propagative at the scale of the system. For small stiffness, multiple scattering prevails, such that waves are diffusive in disconnected fracture networks, and localised in connected ones with a strong multifractality of the intensity field. A re-entrant delocalisation is found in well-connected fracture networks due to energy leakage via evanescent waves and cascades of mode conversion.
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- Lei, Qinghua, et al.
(author)
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Real-Time Forecast of Catastrophic Landslides via Dragon-King Detection
- 2023
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 50:6
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Journal article (peer-reviewed)abstract
- Catastrophic landslides characterized by runaway slope failures remain difficult to predict. Here, we develop a physics-based framework to prospectively assess slope failure potential. Our method builds upon the physics of extreme events in natural systems: the extremes so-called "dragon-kings" (e.g., slope tertiary creeps prior to failure) exhibit statistically different properties than other smaller-sized events (e.g., slope secondary creeps). We develop statistical tools to detect the emergence of dragon-kings during landslide evolution, with the secondary-to-tertiary creep transition quantitatively captured. We construct a phase diagram characterizing the detectability of dragon-kings against "black-swans" and informing on whether the slope evolves toward a catastrophic or slow landslide. We test our method on synthetic and real data sets, demonstrating how it might have been used to forecast three representative historical landslides. Our method can in principle considerably reduce the number of false alarms and identify with high confidence the presence of true hazards of catastrophic landslides.
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- Lei, Qinghua, et al.
(author)
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Transport and Localization of Elastic Waves in Two‐Dimensional Fractured Media : Consequences on Scattering Attenuation
- 2021
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In: Journal of Geophysical Research - Solid Earth. - : American Geophysical Union (AGU). - 2169-9313 .- 2169-9356. ; 126:6
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Journal article (peer-reviewed)abstract
- We present numerical simulations of elastic wave transport in two-dimensional fractured media. Natural fracture systems, following a power-law length scaling, are modeled by the discrete fracture network approach for geometrically representing fracture distributions and the displacement discontinuity method for mechanically computing fracture-wave interactions. The model is validated against analytical solutions for wave reflection, transmission, and scattering by single fractures, and then applied to solve the wavefield evolution in synthetic fracture networks. We find that the dimensionless angular frequency (omega) over tilde = omega Z/kappa plays a crucial role in governing wave transport, where., Z, and. are the angular frequency, seismic impedance, and fracture stiffness, respectively. When. is smaller than the critical frequency (omega) over tilde (c) (approximate to 5), waves are in the extended mode, either propagating (for small.) or diffusing by multiple scattering (for intermediate.); as. exceeds.c, waves become trapped, entering either the Anderson localization regime (kl* approximate to 1) in well- connected fracture systems or the weak localization regime (kl* > 1) in poorly-connected fracture systems, where k is the incident wavenumber and l* is the mean free path length. Consequently, the inverse quality factor Q(-1) scales with. obeying a two-branch power-law dependence, showing significant frequency dependence when (omega) over tilde < <(omega)over tilde>(c) and almost frequency independence when (omega) over tilde > (omega) over tilde (c). Furthermore, when (omega) over tilde < <(omega)over tilde>(c), the wavefield exhibits a weak dependence on fracture network geometry, whereas when (omega) over tilde >(omega) over tilde (c), the fracture network connectivity has an important impact on the wavefield such that strong attenuation occurs in well-connected fracture systems.
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