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PREdiction of NOn-LINear soil behavior (PRENOLIN) is an international benchmark aiming to test multiple numerical simulation codes that are capable of predicting nonlinear seismic site response with various constitutive models. One of the objectives of this project is the assessment of the uncertainties associated with nonlinear simulation of 1D site effects. A first verification phase (i.e., comparison between numerical codes on simple idealistic cases) will be followed by a validation phase, comparing the predictions of such numerical estimations with actual strongmotion recordings obtained at well-known sites. The benchmark presently involves 21 teams and 23 different computational codes. We present here the main results of the verification phase dealing with simple cases. Three different idealized soil profiles were tested over a wide range of shear strains with different input motions and different boundary conditions at the sediment/bedrock interface. A first iteration focusing on the elastic and viscoelastic cases was proved to be useful to ensure a common understanding and to identify numerical issues before pursuing the nonlinear modeling. Besides minor mistakes in the implementation of input parameters and output units, the initial discrepancies between the numerical results can be attributed to (1) different understanding of the expression “input motion” in different communities, and (2) different implementations of material damping and possible numerical energy dissipation. The second round of computations thus allowed a convergence of all teams to the Haskell–Thomson analytical solution in elastic and viscoelastic cases. For nonlinear computations, we investigate the epistemic uncertainties related only to wave propagation modeling using different nonlinear constitutive models. Such epistemic uncertainties are shown to increase with the strain level and to reach values around 0.2 (log10 scale) for a peak ground acceleration of 5 m=s2 at the base of the soil column, which may be reduced by almost 50% when the various constitutive models used the same shear strength and damping implementation.

SUMMARY: We estimate the b-value parameter of the Gutenberg–Richter law for earthquake magnitudes in the early stage of the Costa Marchigiana (Italy) seismic sequence, starting on 2022 November 9, with an ML 5.7 event in the Adriatic sea. In particular, we estimate both the completeness magnitude Mc and the b-value within the first 4 and 7 d after the initial strong event in the sequence. Our work represents a practical example of b-value estimation in 'true' real time, that is, during the seismic sequence, and its possible interpretation in terms of short-term forecasting. We highlight some critical issues to consider both in estimating/intepreting the b-value, and in evaluating the real time estimation of Mc. These issues are mainly due to the fact that preliminary catalogues available in real time are quite different from the revised ones, which are usually delivered after a few months. The criticalities are linked to the raw data recorded at an early-stage, an unreliable evaluation of the Mc with statistical approaches, the Short Term Aftershock Incompleteness entailed after the initial strong event, and the magnitude binning. Our results show that real time estimation of the b-value can give insights into the evolution of an ongoing seismic sequence, when attention is paid to data quality and quantity. [ABSTRACT FROM AUTHOR]

In the present paper, we study derivations of a (n, 2, 1)-nilpotent Lie algebra., UDC 512.55 The simplest (non-abelian) Lie algebras are generalized Heisenberg Lie algebras defined on an (n+1)-dimensional vector space h = V [direct sum] (z) by a nondegenerate alternating form F [...]

In this paper, we carry out a comparison analysis of the Epidemic Type Aftershock Sequence (ETAS) model for the earthquake process, embedded with the three main exponential-type distributions adopted in practical applications to describe the magnitudes of seismic events, that are, the Gutenberg–Richter (GR), the tapered Gutenberg–Richter (TGR) and the CHaracteristic (CH) frequency–magnitude distributions (FMDs). The first law is a pure-power decreasing function, while both the other two introduce a more rapid decay in the tail of the distribution: a soft taper in the TGR model and a sharp cut-off in the CH one. To perform the comparison, we first investigate some theoretical features of the ETAS model with CH-distributed magnitudes (ETAS-CH), which have not been deeply analysed in the literature as much as for ETAS-TGR and ETAS-GR. In particular, we explicitly compute the branching ratio, we analyse its asymptotics in relation to its parameters, and we derive the proper stability conditions. We then move to the comparison among the three ETAS-GR, ETAS-TGR and ETAS-CH processes, to highlight differences and similarities. This is done by carrying out both a theoretical analysis, mainly focused on the three models' branching ratios and the relative sensitivity, and a simulation analysis of realistic synthetic catalogues to compare the processes' numbers, events' magnitude distribution and temporal evolution. The results we obtained show that the ETAS-TGR and ETAS-CH processes have very similar features. They both have also less restrictive non-explosion conditions than for ETAS-GR; in fact, differently from this latter case, their branching ratios exist for any value of the parameters and are lower than the one of ETAS-GR, to which they converge for large magnitudes. [ABSTRACT FROM AUTHOR]

Smart well completion technology for sand management is being used more and more in the petroleum industry to increase productivity and cumulative hydrocarbon production over that of classical sand control techniques. While an understanding of the geomechanics aspects of sand production has begun to emerge, predicting and optimising two-phase oil-sand flow performance characteristics in horizontal wellbores remains a challenge. This theoretical study analysed two-phase, oil-sand suspended flow in a horizontal well by developing a new phenomenological model to predict lift velocity and pressure drop profiles, which are key parameters for designing optimal deployment of horizontal wells in an unconsolidated reservoir. Computations of average pressure drop for two-phase oil-sand flow in a horizontal well are in reasonable agreement with values predicted by a previous model for a relatively wide range of operating conditions. However, the new model eliminates the need for empiricism in predicting the wellbore hydraulics for oil-sand multiphase flow in horizontal wells and is applicable to different wellbore geometries. The proposed computational methodology has been applied to a hypothetical case study to demonstrate its field applicability. Les techniques de complétions intelligentes de puits avec gestion de venues de sable sont de plus en plus utilisées dans l’industrie pétrolière. Comparées aux techniques classiques de gestion de venues de sable, elles améliorent la productivité et la production cumulée d’hydrocarbures. Cependant, alors que les aspects géomécaniques de la production de sable sont de mieux en mieux appréhendés, la prévision et l’optimisation des écoulements diphasiques huile-sable dans les puits horizontaux posent toujours problème. Dans cette étude, une analyse théorique de l’écoulement d’un mélange huile-sable en suspension dans un puits horizontal a été effectuée. Pour ce faire, des modèles phénoménologiques ont été développés pour prédire la vitesse de remontée optimale ainsi que les profils de perte de charge, qui sont les deux paramètres clés pour optimiser la conception d’un puits horizontal dans un réservoir non consolidé. Le calcul de la perte de charge moyenne pour un écoulement diphasique huile-sable dans un puits horizontal est en accord avec les valeurs prédites par un modèle précédent, même pour des conditions d’opération variées. Cependant, le nouveau modèle évite de recourir à l’empirisme pour prévoir le comportement du puits dans le cas d’un écoulement multiphasique. Il peut également être appliqué à différentes géométries de puits. La méthode de calcul proposée a été testée sur une étude de cas hypothétique, afin de démontrer son applicabilité sur le terrain.