Consideration Of Epistemic Uncertainties Research Articles

Post-earthquake fire ignition model uncertainty in regional probabilistic shaking–fire cascading multi-hazard risk assessment: A study of earthquakes in Japan

Fires following earthquakes have significant impact on urban communities in earthquake-prone countries with wooden buildings, in addition to the main earthquake hazard of ground shaking. Regional-scale post-earthquake fire risk assessments are important for developing effective risk reduction strategies. Such risk assessments require the consideration of epistemic uncertainty, that is, uncertainty caused by lack of knowledge concerning the best models, in addition to aleatoric uncertainty. This study focused on epistemic uncertainty in post-earthquake fire ignition estimations, and incorporated it into risk assessments by using alternative empirical ignition models. The key objectives of this study were as follows: (1) correlating the probability of ignition per person to the ground motion intensity based on data for different past large earthquakes in Japan; (2) investigating the impact of using ignition models calibrated on different earthquake events in risk assessments through a realistic case study considering possible large earthquakes. A hierarchical Bayesian Poisson regression analysis revealed that the empirical relationship between the ignition probability and ground motion intensity greatly varies across six major large earthquakes in Japan from 1995 to 2022. Particularly, the effects of ignition prevention measures that have been widely implemented in households since the 1995 Kobe earthquake were inferred from much smaller ignition probabilities in approximately the last 10 years. The effects of this high epistemic uncertainty manifested as the large variability of the loss exceedance curve for a portfolio of buildings. These results indicate that the new ignition models can help to foster risk-informed decision-making under epistemic uncertainty.

Time-dependent reliability of structures under consideration of epistemic uncertainty

Time-dependent reliability of structures under consideration of epistemic uncertainty

Predeformed geometrically exact beam model for a dynamic‐response prosthesis

AbstractClinical trials have shown that the storage and release of energy in prosthetic feet plays a major role in the resulting walking comfort for the patient. In comparison to rigid multi‐axis prosthetic feet, dynamic‐response prosthetic feet show good energy storage and release capabilities and thereby increase the walking comfort of the patient. To accurately simulate such a prosthesis in a gait cycle simulation, its model has to represent the deformation energy as accurately as possible.Based on the theory of predeformed geometrically exact beams [1], this work proposes a model for a carbon spring foot prosthesis, continuing the work from [3]. The model is based on the Össur Vari‐Flex®, which has been non destructively reverse engineered resulting in a CAD representation and various parameters. Additionally, the parameters for density and elasticity and shear modulus were refined with parameter optimisation [4]. The geometrically exact beam model of the prosthesis offers a good representation of the deformation energy for large deformations occurring during the gait cycle while reducing the computational cost. The model's implementation is validated numerically and a brief mesh study is performed.The next step is the consideration of epistemic uncertainty and to investigate its influence on the prediction of the energy storage and release capabilities of the prosthesis.

Towards consideration of epistemic uncertainty in shear-wave velocity measurements obtained via seismic cone penetration testing (SCPT)

Seismic cone penetration testing (SCPT) is a powerful geotechnical site characterization tool, allowing for simultaneous collection of routine cone penetration testing data and rapid downhole-type measurements of shear-wave velocity (VS). However, the uncertainties associated with developing VS profiles from SCPT measurements are rarely considered or communicated to the end-user. One important source of VS uncertainty is related to how the shear wave travel times are interpreted from the recorded waveforms, while another critical source of uncertainty is related to the analysis method used to transform the travel times to velocities. In this study, four common ways of obtaining travel times were considered: (i) first arrival picks, (ii) peaks and troughs picks, (iii) crossover picks, and (iv) the peak response of the cross-correlation function. Using these different travel times, a number of VS profiles were developed using four different velocity analysis methods: (i) pseudo-interval, (ii) true-interval, (iii) corrected vertical travel time slope-based, and (iv) raytracing. Through consideration of multiple wave arrival time and velocity analysis methods, a robust and meaningful quantification of the intramethod, depth-dependent epistemic uncertainty in VS obtained from several example SCPT datasets has been developed. VS uncertainty is further examined through consideration of the intermethod variability and bias between SCPT and direct-push crosshole testing.

Time-dependent probabilistic tsunami hazard analysis using stochastic rupture sources

This study conducts a time-dependent probabilistic tsunami hazard analysis using stochastic rupture sources, which enables the consideration of numerous heterogeneous earthquake slip distributions. Earthquake occurrence modeling is based on temporal renewal and magnitude recurrence models. To account for various combinations of alternative models for temporal occurrence process, earthquake magnitude distribution, and spatial earthquake slip distribution, a logic-tree approach is implemented, facilitating more comprehensive characterization of epistemic uncertainties for the stochastic rupture source approach. To demonstrate the effects of different model components on tsunami hazard curves, a case study for coastal plain areas of Miyagi Prefecture in Japan is set up. The sensitivity analysis clearly indicates that the selection of renewal and magnitude models has paramount influence on the tsunami hazard results. The results also depend on the situations of interest in terms of current time and time-horizon with respect to the recurrence process of the earthquake rupture. In light of significant uncertainties of tsunami hazard and risk due to future mega-thrust subduction events, consideration of epistemic uncertainties is of critical importance.

Critical Issues on Probabilistic Earthquake Loss Assessment

ABSTRACTProbabilistic loss modeling can be used to develop risk reduction measures, such as the identification of regions more prone to human and economic losses, or to develop financial mechanisms to transfer the earthquake risk from local governments to the private sector. This study addresses several critical issues in probabilistic loss modeling, and provides recommendations depending on the intended final use of the risk results. Modeling issues related to convergence in probabilistic event-based analysis; consideration of epistemic uncertainties within a logic tree; generation of different types of loss exceedance curves; and derivation of risk maps are thoroughly investigated. The Metropolitan Area of Lisbon is used to explore these issues, and it is demonstrated that different assumptions in the loss modeling process can lead to considerably different risk results. Furthermore, the findings and recommendations of this study are also relevant for institutions that promote the assessment of earthquake hazard and risk, such as the Global Earthquake Model Foundation.

Ground-motion characterization for the probabilistic seismic hazard assessment in Turkey

This study describes the methodology implemented to establish the ground-motion logic-tree for national probabilistic seismic hazard map of Turkey for shallow active crustal regions. The presented procedure provides quantitative information to guide the hazard experts while establishing the logic tree to capture the epistemic uncertainty in ground-motion characterization. It uses non-data-driven and data-driven testing methods to identify and rank candidate ground-motion prediction equations (GMPEs) under a specific ground-motion database. The candidate GMPEs are subjected to visual inspection and are classified into center, body and range (CBR) spectral estimates for a proper consideration of epistemic uncertainty. The GMPEs classified into CBR are then used in a suite of seismic hazard sensitivity analysis to establish the most suitable GMPE logic-tree whose spectral estimates are not biased by any one of the GMPEs in the logic-tree structure. The sensitivity analysis considers normalized spectral ordinates and is not manipulated by the spectral amplitudes. The proposed procedure is inherited from the relevant studies of the Earthquake Model of the Middle East (EMME; www.efehr.org:8080/jetspeed/portal/emme.psml) regional seismic hazard project. This paper also highlights the similarities and differences in ground-motion characterization between EMME and our approach.

Development of methodology of probabilistic safety assessment for radioactive waste disposal in consideration of epistemic uncertainty and aleatory uncertainty

ABSTRACTProbabilistic safety assessment has not been performed for radioactive waste disposal owing to the difficulty of dealing with the probability distributions of the parameters included in the long-term safety assessment of radioactive waste disposal. In this study, we develop a methodology of probabilistic safety assessment in consideration of both epistemic uncertainty and aleatory uncertainty, in which the probability density function (PDF) and cumulative distribution function (CDF) of the maximum annual dose can be calculated. We also propose an approach to demonstrating dose assessment results in compliance with the stepwise target annual doses of likely and less-likely scenarios according to the occurrence probability of the scenario without classifying the probabilities of parameters involved prior to the safety assessment. For the likely scenario, we can employ the larger of the modal value of the PDF and the 50th percentile of the CDF to meet the target annual dose (10 µSv y-1). For the less-likely scenario, we can adopt the 95th percentile of the CDF as the assessment result for comparison with the target annual dose (300 µSv y-1).

An approach for exploring the dynamical behaviour of inhomogeneous structural inclusions under consideration of epistemic uncertainty

PurposeThe purpose of this paper is to analyze the wave scattering behaviour of an inhomogeneous and eccentric inclusion in a homogeneous matrix material. Another purpose is to evaluate the influence of epistemic uncertainty on the wave scattering behaviour, particularly on the lack of knowledge about this eccentricity. This task calls for a multidisciplinary model.Design/methodology/approachThe inclusion is modelled as a multi‐layered obstacle, with all layers being eccentric with respect to each other. The material behaviour of the embedding matrix is linear elastic and isotropic. In a multidisciplinary approach, the interaction of the inhomogeneous inclusion and the embedding matrix with respect to an incoming shear wave of arbitrary shape is solved analytically. The purely analytical solution process takes place in the frequency‐domain. Due to the lack of knowledge about the eccentric configuration of the matrix inclusion and its influence on the total wave field inside the matrix material, the mechanical model is coupled with fuzzy set theory for modelling this non‐stochastic uncertainty.FindingsAn analytical model for describing the wave scattering behaviour of an elastic matrix inclusion with eccentric set‐up is found and intimately connected with the framework of fuzzy set theory. Hence it is shown that the treatment of epistemic uncertainty with the derived analytical model is possible and fruitful. Additionally, it is shown that eccentric configurations lead to highly increased amplitudes with respect to the reference case of a concentric or even homogenous set‐up of the inclusion.Originality/valueThe value of this contribution is in the analytical model, which allows one to predict the wave scattering behaviour of eccentric configurations of multi‐layered fibres including the surrounding interphase, and its coupling with fuzzy set theory to cope with the epistemic uncertainty inherent in the geometric set‐up of the matrix inclusion.

The impact of modelling uncertainties on the seismic performance assessment of reinforced concrete frame buildings

Simplified procedures have been used for the estimation of seismic response parameters by considering the epistemic uncertainties for an older reinforced concrete frame, and for two contemporary reinforced concrete structures. The simplifications in the procedure are associated with a simplified nonlinear method and models for the assessment of the seismic performance of the structure, whereas the effects of the epistemic uncertainty are treated by using the first-order-second-moment (FOSM) method, and the latin hypercube sampling (LHS) technique. The results of sensitivity analysis reveal that it is those parameters which affect the collapse mechanism and have a high coefficient of variation that have the greatest impact on the seismic response parameters for the near collapse limit state. The results of uncertainty analysis by using the LHS technique showed that epistemic uncertainties have an effect on the dispersion, and also on the median estimates of the response parameters. For all three example structures a reduction in the estimate for the median peak ground acceleration at the near-collapse limit state was observed. Thus, explicit consideration of epistemic uncertainties in the process of the assessment of structural performance can lead to more accurate results, and consequently also to more reliable assessment of seismic risk.

Consideration and Propagation of Epistemic Uncertainties in New Zealand Probabilistic Seismic-Hazard Analysis

This article presents results from the consideration of epistemic uncertainties in New Zealand (NZ) probabilistic seismic‐hazard analysis. Uncertainties in ground‐motion prediction are accounted for via multiple ground‐motion prediction equations within the logic‐tree framework. Uncertainties in the fault‐based seismicity of the earthquake rupture forecast due to uncertainties in fault geometry, slip parameters, and magnitude‐scaling relationships are considered in a Monte Carlo simulation framework. Because of the present lack of fault‐specific data quantifying uncertainties for many faults in NZ, representative values based on judgement and available data for NZ and foreign faults were utilized. Uncertainties in the modelling of background seismicity were not considered. The implications of the considered epistemic uncertainties in terms of earthquake magnitude–frequency distributions and probabilistic seismic‐hazard analyses for two spectral acceleration ordinates, two soil classes, and two locations (Wellington and Christchurch) are examined. The results illustrate that, for the uncertainties considered, the variation in seismic hazard due to the adopted ground‐motion prediction model is larger than that due to the uncertainties in the earthquake rupture forecast. Of the earthquake rupture forecast uncertainties considered, the magnitude‐geometry scaling relationships was the most significant, followed by fault rupture length. Hence, the obtained results provide useful guidance on which modelling issues are the most critical in the reliability of seismic‐hazard analyses for locations in NZ.

Empirical correlation of PGA, spectral accelerations and spectrum intensities from active shallow crustal earthquakes

AbstractEmpirical correlation equations between peak ground acceleration, spectral acceleration, spectrum intensity, and acceleration spectrum intensity are developed. The correlation equations are developed for shallow crustal earthquakes using the Next Generation Attenuation (NGA) ground motion database, and four of the NGA ground motion prediction equations (GMPEs). A particularly novel aspect of the present study is the explicit consideration of epistemic uncertainty in the correlation equations due to both the adopted ground motion database and GMPEs. The resulting correlation equations enable the joint consideration of these four ground motion intensity measures in ground motion selection using frameworks such as the generalized conditional intensity measure approach. Copyright © 2011 John Wiley & Sons, Ltd.

Epistemic Uncertainties in Component Fragility Functions

This paper is concerned with the inclusion of epistemic uncertainties in component fragility functions used in performance-based earthquake engineering. Conventionally fragility functions, defining the probability of incurring at least a specified level of damage for a given level of seismic demand, are defined by a mean and standard deviation and assumed to have a lognormal distribution. However, there exist many uncertainties in the development of such fragility functions. The sources of epistemic uncertainty in fragility functions, their consideration, combination, and propagation are presented and discussed. Two empirical fragility functions presented in literature are used to illustrate the epistemic uncertainty in the fragility function parameters due to the finite size of the datasets. These examples and the associated discussions illustrate that the magnitude of epistemic uncertainties are significant and there are clear benefits of the consideration of epistemic uncertainties pertaining to the documentation, quality assurance, implementation, and updating of fragility functions. Epistemic uncertainties should therefore always be addressed in future fragility functions developed for use in seismic performance assessment.