Nucleation of rupture under slip dependent friction law: Simple models of fault zone

The initiation of frictional instability is investigated for simple models of fault zone using a linearized perturbation analysis. The fault interface is assumed to obey a linear slip-weakening law. The fault is initially prestressed uniformly at the sliding threshold. In the case of antiplane shear between two homogeneous linearly elastic media, space-time and spectral solutions are obtained and shown to be consistent. The nucleation is characterized by (1) a long-wavelength unstable spectrum bounded by a critical wave number; (2) an exponential growth of the unstable modes; and (3) an induced off-fault deformation that remains trapped within a bounded zone in the vicinity of the fault. These phenomena are characterized in terms of the elastic parameters of the surrounding medium and a nucleation length that results from the coupling between the frictional interface and the bulk elasticity. These results are extended to other geometries within the same formalism and implications for three-dimensional rupture are discussed. Finally, internal fault structures are investigated in terms of a fault-parallel damaged zone. Spectral solutions are obtained for both a smooth and a layered distribution of damage. For natural faults the nucleation is shown to depend strongly on the existence of a internal damaged layer. This nucleation can be described in terms of an effective homogeneous model. In all cases, frictional trapping of the deformation out of the fault can lead to the property that arbitrarily long wavelengths remain sensitive to the existence of a fault zone

Modeling seismic wave propagation and amplification in 1D/2D/3D linear and nonlinear unbounded media

To analyze seismic wave propagation in geological structures, it is possible to consider various numerical approaches: the finite difference method, the spectral element method, the boundary element method, the finite element method, the finite volume method, etc. All these methods have various advantages and drawbacks. The amplification of seismic waves in surface soil layers is mainly due to the velocity contrast between these layers and, possibly, to topographic effects around crests and hills. The influence of the geometry of alluvial basins on the amplification process is also know to be large. Nevertheless, strong heterogeneities and complex geometries are not easy to take into account with all numerical methods. 2D/3D models are needed in many situations and the efficiency/accuracy of the numerical methods in such cases is in question. Furthermore, the radiation conditions at infinity are not easy to handle with finite differences or finite/spectral elements whereas it is explicitely accounted in the Boundary Element Method. Various absorbing layer methods (e.g. F-PML, M-PML) were recently proposed to attenuate the spurious wave reflections especially in some difficult cases such as shallow numerical models or grazing incidences. Finally, strong earthquakes involve nonlinear effects in surficial soil layers. To model strong ground motion, it is thus necessary to consider the nonlinear dynamic behaviour of soils and simultaneously investigate seismic wave propagation in complex 2D/3D geological structures! Recent advances in numerical formulations and constitutive models in such complex situations are presented and discussed in this paper. A crucial issue is the availability of the field/laboratory data to feed and validate such models.Comment: of International Journal Geomechanics (2010) 1-1

Basin Effects in Strong Ground Motion: A Case Study from the 2015 Gorkha, Nepal Earthquake

The term "basin effects" refers to entrapment and reverberation of earthquake waves in soft sedimentary deposits underlain by concave basement rock structures. Basin effects can significantly affect the amplitude, frequency and duration of strong ground motion, while the cone-like geometry of the basin edges gives rise to large amplitude surface waves through seismic wave diffraction and energy focusing, a well-known characteristic of basin effects. In this research, we study the role of basin effects in the mainshock ground motion data recorded at the Kathmandu basin, Nepal during the 2015 Mw7.8 Gorkha earthquake sequence. We specifically try to understand the source of the unusual low frequency reverberating pulse that appeared systematically across the basin, and the unexpected depletion of the ground surface motions from high frequency components, especially away from the basin edges. In order to do that we study the response of a 2D cross section of Kathmandu basin subjected to vertically propagating plane SV waves. Despite the scarcity of geotechnical information and of strong ground motion recordings, we show that an idealized plane-strain elastic model with a simplified layered velocity structure can capture surprisingly well the low frequency components of the basin ground response. We finally couple the 2D elastic simulation with a 1D nonlinear analysis of the shallow basin sediments. The 1D nonlinear approximation shows improved performance over a larger frequency range relative to the first order approximation of a 2D elastic layered basin response.Comment: Geotechnical Earthquake Engineering and Soil Dynamics V, Austin, Texas (2018

A new fast multi-domain BEM to model seismic wave propagation and amplification in 3D geological structures

International audienceThe analysis of seismic wave propagation and amplification in complex geological structures raises the need for efficient and accurate numerical methods. The solution of the elastodynamic equations using traditional boundary element methods (BEMs) is greatly hindered by the fully-populated nature of the matrix equations arising from the discretization. In a previous study limited to homogeneous media, the present authors have established that the Fast Multipole (FM) method reduces the complexity of a 3-D elastodynamic BEM to $N \log N$ per GMRES iteration and demonstrated its effectiveness on 3-D canyon configurations. In this article, the frequency-domain FM-BEM methodology is extented to 3-D elastic wave propagation in piecewise-homogeneous domains in the form of a FM-accelerated multi-region BE-BE coupling approach. This new method considerably enhances the capability of the BEM for studying the propagation of seismic waves in 3-D alluvial basins of arbitrary geometry embedded in semi-infinite media. Several fully 3-D examples (oblique SV-waves) representative of such configurations validate and demonstrate the capabilities of the multi-domain fast multipole approach. They include comparisons with available (low-frequency) results for various types of incident wavefields, and time-domain results obtained by means of Fourier synthesis

Clonal chromosomal mosaicism and loss of chromosome Y in elderly men increase vulnerability for SARS-CoV-2

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, COVID-19) had an estimated overall case fatality ratio of 1.38% (pre-vaccination), being 53% higher in males and increasing exponentially with age. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, we found 133 cases (1.42%) with detectable clonal mosaicism for chromosome alterations (mCA) and 226 males (5.08%) with acquired loss of chromosome Y (LOY). Individuals with clonal mosaic events (mCA and/or LOY) showed a 54% increase in the risk of COVID-19 lethality. LOY is associated with transcriptomic biomarkers of immune dysfunction, pro-coagulation activity and cardiovascular risk. Interferon-induced genes involved in the initial immune response to SARS-CoV-2 are also down-regulated in LOY. Thus, mCA and LOY underlie at least part of the sex-biased severity and mortality of COVID-19 in aging patients. Given its potential therapeutic and prognostic relevance, evaluation of clonal mosaicism should be implemented as biomarker of COVID-19 severity in elderly people. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, individuals with clonal mosaic events (clonal mosaicism for chromosome alterations and/or loss of chromosome Y) showed an increased risk of COVID-19 lethality

Anales del III Congreso Internacional de Vivienda y Ciudad "Debate en torno a la nueva agenda urbana"

Acta de congresoEl III Congreso Internacional de Vivienda y Ciudad “Debates en torno a la NUEVa Agenda Urbana”, ha sido una apuesta de alto compromiso por acercar los debates centrales y urgentes que tensionan el pleno ejercicio del derecho a la ciudad. Para ello las instituciones organizadoras (INVIHAB –Instituto de Investigación de Vivienda y Hábitat y MGyDH-Maestría en Gestión y Desarrollo Habitacional-1), hemos convidado un espacio que se concretó con potencia en un debate transdisciplinario. Convocó a intelectuales de prestigio internacional, investigadores, académicos y gestores estatales, y en una metodología de innovación articuló las voces académicas con las de las organizaciones sociales y/o barriales en el Foro de las Organizaciones Sociales que tuvo su espacio propio para dar voz a quienes están trabajando en los desafíos para garantizar los derechos a la vivienda y los bienes urbanos en nuestras ciudades del Siglo XXI

Scattering and diffraction of elastic Pand S-waves by a spherical obstacle: A review of the classical solution

Rederivamos la solución para el cálculo de la difracción y dispersión de ondas elásticas por una obstrucción esférica. Se presenta un catálogo para los coeficientes en las expansiones de las series de las ondas difractadas. La solución clásica consiste en una superposición de los campos incidente y difractado. Se asumen ondas planas P y S. Ellas se expresan como expansiones de funciones de onda esféricas, las cuales son probadas contra resultados exactos. El campo difractado se calcula a partir de la imposición analítica de condiciones de frontera en la interfase matriz-difractor. La obstrucción puede ser una cavidad, una inclusión elástica o una esfera fluida. Se proporciona un conjunto completo de funciones de onda en términos de funciones radiales esféricas de Bessel y de Hankel. Para las coordenadas angulares se utilizan polinomios de Legendre y funciones trigonométricas. Se muestran resultados en el dominio del tiempo y la frecuencia. Reportamos espectros de amplitudes del desplazamiento contra la frecuencia normalizada y patrones de radiación en frecuencias bajas, medias y altas. Se calculan sismogramas sintéticos para algunos casos relevantes. PALABRA