During an earthquake, part of the released elastic strain energy is dissipated within the slip zone by frictional and fracturing processes, the rest being radiated away via elastic waves. While ...frictional heating plays a key role in the energy budget of earthquakes, it could not be resolved by seismological data up to now. Here we investigate the dynamics of laboratory earthquakes by measuring frictional heat dissipated during the propagation of shear instabilities at stress conditions typical of seismogenic depths. We estimate the complete energy budget of earthquake rupture and demonstrate that the radiation efficiency increases with thermal‐frictional weakening. Using carbon properties and Raman spectroscopy, we map spatial heat heterogeneities on the fault surface. We show that an increase in fault strength corresponds to a transition from a weak fault with multiple strong asperities and little overall radiation, to a highly radiative fault behaving as a single strong asperity.
Plain Language Summary
In nature, earthquakes occur when the stress accumulated in a medium is released by frictional sliding on faults. The stress released is dissipated into fracture and heat energy or radiated through seismic waves. The seismic efficiency of an earthquake is a measure of the fraction of the energy that is radiated away into the host medium. Because faults are at inaccessible depths, we reproduce earthquakes in the laboratory under natural in situ conditions to understand the physical processes leading to dynamic rupture. We estimate the first complete energy budget of an earthquake and show that increasing heat dissipation on the fault increases the radiation efficiency. We develop a novel method to illuminate areas of the fault that get excessively heated up. We finally introduce the concept of spontaneously developing heat asperities, playing a major role in the radiation of seismic waves during an earthquake.
Key Points
Spatial heat heterogeneities are imaged on a frictional interface using carbon properties and Raman spectroscopy
Rupture processes become more efficient with increasing slip on fault
Heating efficiency depends on time‐dependent memory effect of the fault surface
The maximum height of an explosive volcanic column, H, depends on the 1/4th power of the eruptive mass flux, Q, and on the 3/4th power of the stratification of the atmosphere, N. Expressed as scaling ...laws, this relationship has made H a widely used proxy to estimate Q. Two additional effects are usually included to produce more accurate and robust estimates of Q based on H: particle sedimentation from the volcanic column, which depends on the total grain-size distribution (TGSD) and the atmospheric crosswind. Both coarse TGSD and strong crosswind have been shown to decrease strongly the maximum column height, and TGSD, which also controls the effective gas content in the column, influences the stability of the column. However, the impact of TGSD and of crosswind on the dynamics of the volcanic column are commonly considered independently. We propose here a steady-state 1D model of an explosive volcanic column rising in a windy atmosphere that explicitly accounts for particle sedimentation and wind together. We consider three typical wind profiles: uniform, linear, and complex, with the same maximum wind velocity of 15ms−1. Subject to a uniform wind profile, the calculations show that the maximum height of the plume strongly decreases for any TGSD. The effect of TGSD on maximum height is smaller for uniform and complex wind profiles than for a linear profile or without wind. The largest differences of maximum heights arising from different wind profiles are observed for the largest source mass fluxes (>107kgs−1) for a given TGSD. Compared to no wind conditions, the field of column collapse is reduced for any wind profile and TGSD at the vent, an effect that is the strongest for small mass fluxes and coarse TGSD. Provided that the maximum plume height and the wind profile are known from real-time observations, the model predicts the mass discharge rate feeding the eruption for a given TGSD. We apply our model to a set of eight historical volcanic eruptions for which all the required information is known. Taking into account the measured wind profile and the actual TGSD at the vent substantially improves (by ≈30%) the agreement between the mass discharge rate calculated from the model based on plume height and the field observation of deposit mass divided by eruption duration, relative to a model taking into account TGSD only. This study contributes to the improvement of the characterization of volcanic source term required as input to larger scale models of ash and aerosol dispersion.
•We detail a model of volcanic plumes that includes wind effect and particle fallout.•We validate the model against a specially assembled data set of Plinian eruptions.•We show that the atmospheric wind profile strongly affects the rise of the column.•Predictions of eruptive mass flux from plume height are significantly improved.
Temporal variations of radon concentration, or spatial variations around geothermal systems, are partly driven by the effect of temperature on the radon source term, the effective radium ...concentration (ECRa). ECRa from 12 crushed rock and 12 soil samples from Nepal was measured in the laboratory using the radon accumulation method and Lucas scintillation flasks at three temperatures: 7, 22 and 37 °C. For each sample and at each temperature, 5 or 6 measurements were carried out, representing a total of 360 measurements, with an ECRa average varying from 1.1 to 75 Bq kg−1. While the effect is small, ECRa was observed to increase with temperature in a significant and sufficiently reproducible manner. The increase was approximately linear with a slope (temperature sensitivity, TS) expressed in % °C−1. We observed a large heterogeneity of TS with average values (range min-max) of 0.79 ± 0.05 (0.16–2.0) % °C−1 and 0.61 ± 0.05 (0.10–2.0) % °C−1, for rock and soil samples, respectively. While this range overlaps with the results of previous studies, our values of TS tend to be smaller. The observed heterogeneity implies that the TS, rather poorly understood, needs to be assessed by dedicated experiments in every case where it is of consequence for the interpretation.
Integrated Ocean Drilling Program (IODP) Expedition 316 Sites C0006 and C0007 examined the deformation front of the Nankai accretionary prism offshore the Kii Peninsula, Japan. In the drilling area, ...the frontal thrust shows unusual behavior as compared to other regions of the Nankai Trough. Drilling results, integrated with observations from seismic reflection profiles, suggest that the frontal thrust has been active since ∼0.78–0.436 Ma and accommodated ∼13 to 34% of the estimated plate convergence during that time. The remainder has likely been distributed among out‐of‐sequence thrusts further landward and/or accommodated through diffuse shortening. Unlike results of previous drilling on the Nankai margin, porosity data provide no indication of undercompaction beneath thrust faults. Furthermore, pore water geochemistry data lack clear indicators of fluid flow from depth. These differences may be related to coarser material with higher permeability or more complex patterns of faulting that could potentially provide more avenues for fluid escape. In turn, fluid pressures may affect deformation. Well‐drained, sand‐rich material under the frontal thrust could have increased fault strength and helped to maintain a large taper angle near the toe. Recent resumption of normal frontal imbrication is inferred from seismic reflection data. Associated décollement propagation into weaker sediments at depth may help explain evidence for recent slope failures within the frontal thrust region. This evidence consists of seafloor bathymetry, normal faults documented in cores, and low porosities in near surface sediments that suggest removal of overlying material. Overall, results provide insight into the complex interactions between incoming materials, deformation, and fluids in the frontal thrust region.
Low-field magnetic susceptibility χm and effective radium concentration ECRa, obtained from radon emanation, have been measured in the laboratory with 129 soil samples from Nepal. Samples along ...horizontal profiles in slope debris or terrace scarps showed rather homogeneous values of both χm and ECRa. One sample set, collected vertically on a lateritic terrace scarp, had homogeneous values of ECRa while χm increased by a factor of 1 to 10 for residual soils and topsoils. However, for a set of samples collected on three imbricated river terraces, values of ECRa, homogeneous over a given terrace, displayed a gradual increase from younger to older terraces. By contrast, χm showed more homogeneous mean values over the three terraces, with a larger dispersion, however, for the younger one. Similarly, Kathmandu sediments exhibited a large increase in ECRa from sand to clay layers, while χm increased moderately. The combination of χm and ECRa, thus, provides a novel tool to characterize quantitatively various soil groups and may be of interest to distinguish modes of alteration or deposition histories.
This study addresses the estimation of material properties at a mesoscopic level using the PuMA software from an uncertainty quantification perspective. Stochastic simulation with PuMA is primarily ...related to the random distribution of fibers, which is an intrinsic source of uncertainty. Additionally, the selection of certain physical parameters, such as the fiber's thermal conductivity, introduces further uncertainties. The first contribution of this study is to propose a low-cost surrogate-based methodology with an unequal allocation scheme, applied for the first time to the stochastic mesoscale characterization of ablative materials. The second contribution is a study on uncertainty propagation and sensitivity analysis of material properties, providing a systematic assessment of the choice of voxel resolution for both the fibers and the domain. Specifically, the convergence of quantities of interest can be monitored, thus identifying the minimal reference elementary volume.
•Building surrogate to compute statistics of material properties of a stochastic solver.•First-ever assessment of material properties at mesoscopic level using PuMA under Uncertainty Quantification.•Assessment of the choice of the voxel resolution surveying convergence, identifying minimal reference elementary volume.•Thermal conductivity variance explained by uncertainty on porosity for in-plane conductivity.
This study compares and evaluates one-dimensional (1D) and three-dimensional (3D) numerical models of volcanic eruption columns in a set of different inter-comparison exercises. The exercises were ...designed as a blind test in which a set of common input parameters was given for two reference eruptions, representing a strong and a weak eruption column under different meteorological conditions. Comparing the results of the different models allows us to evaluate their capabilities and target areas for future improvement. Despite their different formulations, the 1D and 3D models provide reasonably consistent predictions of some of the key global descriptors of the volcanic plumes. Variability in plume height, estimated from the standard deviation of model predictions, is within ~20% for the weak plume and ~10% for the strong plume. Predictions of neutral buoyancy level are also in reasonably good agreement among the different models, with a standard deviation ranging from 9 to 19% (the latter for the weak plume in a windy atmosphere). Overall, these discrepancies are in the range of observational uncertainty of column height. However, there are important differences amongst models in terms of local properties along the plume axis, particularly for the strong plume. Our analysis suggests that the simplified treatment of entrainment in 1D models is adequate to resolve the general behaviour of the weak plume. However, it is inadequate to capture complex features of the strong plume, such as large vortices, partial column collapse, or gravitational fountaining that strongly enhance entrainment in the lower atmosphere. We conclude that there is a need to more accurately quantify entrainment rates, improve the representation of plume radius, and incorporate the effects of column instability in future versions of 1D volcanic plume models.
•We present the main results of an eruptive column model inter-comparison exercise.•Simulations with standard inputs for strong and weak eruptive plumes were performed.•We compare results of empirical, one-dimensional, and three-dimensional models.•Results allowed for evaluating model capabilities and areas for model improvement.
Senescence is associated with a decreased activity of enzyme delta-6 desaturase, which converts linoleic acid to gamma-linolenic acid. This enzymatic defect may alter the composition of plasma and ...membrane lipids, and influences the biosynthesis of renal prostaglandins. Exogenous supplementation of GLA during 3 months increases the plasma level of dihomo-gamma-linolenic acid (p < 0.002), and to a smaller degree, the level in erythrocyte membrane lipids. This treatment was associated with a beneficial reduction of cardiovascular risk factors (arterial hypertension, total cholesterol, apolipoprotein B, HDL-cholesterol, apolipoprotein A-I) and the renal function has become stable reached. Epogam treatment also increased the biosynthesis of renal prostaglandins, especially that of prostaglandin E2, which has a vasodilatory effect on vessel walls and reduces the elevated blood pressure.
Dietary supplementation of essential fatty acids such as gamma-linolenic acid to old subjects has beneficial effect on their health condition. (Tab. 6, Fig. 5, Ref. 37.)
Le « ségrographe » est un graphique qui croise la dispersion statistique d'une variable (mesurée par exemple par l'indice de ségrégation de Duncan) et sa cohésion spatiale (mesurée par exemple par ...l'indice d'autocorrélation de Geary). Il constitue une aide à la typologie de différenciations sociospatiales, que nous appliquons dans cet article aux espaces urbains. L'approche statistique par agrégats collectifs (démarche écologique) apparaît pourtant souvent réductrice pour comprendre des logiques de ségrégations, largement conditionnées par des trajectoires individuelles. Par la représentation sur le « ségrographe » de données comportementales, tels les résultats électoraux, nous faisons l'hypothèse inverse que les comportements individuels sont également conditionnés par un environnement collectif, et que cet effet d'entraînement est mesurable par des outils d'analyse spatiale (autocorrélation, dispersion statistique, effets de structure). The « segrograph » is a chart that compares the dispersion of a variable (measured by Duncan's index of segregation, for example) with its spatial cohesion (measured by Geary's index of spatial autocorrelation, for example). It assists the typology of socio-spatial differentiation, which is applied to urban areas in this paper. The statistical approach by collective aggregates (ecological approach) is often too simplistic to understand logics of segregation, largely conditioned by individual trajectories. By using the segrograph to chart behavioural data, such as election results, we can make the reverse hypothesis that individual behaviour is also conditioned by a collective environment and that this bandwagon effect can be measured with spatial analysis tools (autocorrelation, dispersion, structure effects).
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