Tilte - Recent Developments in Site Response Analysis and Microzonation

Abstract: The basic purpose of site response analysis is to evaluate possible local site effects and the earthquake characteriscs on the ground surface to estimate probable earthquake damage for the existing building stock and for the design of new structures. The basic issues in the site response analysis are the inherent uncertainty in source characteristics, soil profile, soil properties, and site response analysis procedure. In addition, characteristics of the building inventories would introduce critical uncertainties associated with these analyses. Recent advances, with growing computational capacity, emphasize probabilistic frameworks to capture these uncertainties. The probability distribution of the related earthquake parameters on the ground surface may be determined considering all possible input acceleration time histories, site profiles, and dynamic soil properties. One option to account for the variability in earthquake source and path effects may be to consider using large number of acceleration records compatible with the site-dependent earthquake hazard partially based on  hazard deaggregation at the investigated site. Likewise, stochastic soil profiles generated via Monte Carlo simulations can be used to account for the site condition variability. A comprehensive seismic microzonation methodology is proposed based on the probabilistic assessment of these factors involved in site response analyses. The second important issue is the selection of microzonation parameters. The selection of microzonation parameters—such as Cumulative Absolute Velocity (CAV) and Housner Intensity (HI)—is emphasized for their stronger empirical correlation with structural damage. The main approach is to develop a microzonation procedure for ground shaking intensity accounting for variability in ground motion and soil response. The third issue is the reliability and correctness of the site response analysis procedure. The adopted methodology advances traditional site response analysis by integrating frequency- and stress-dependent soil behavior models to achieve a more accurate numerical model and proposing the use of 3D site response analysis to reflect the multi-directional nature of seismic loading. It also highlights the need for representative time histories with known exceedance probabilities. Even though the selected representative acceleration time histories may be scaled with respect to probabilistic acceleration spectrum or peakground acceleration obtained based on probabilistic site response analysis; the probability of the selected acceleration time histories are not known. The only possible option is to estimate probabilistic acceleration time histories with predetermined exceedance probabilities to enhance fully probabilistic site response analysis. The proposed methodology is demonstrated through case studies based on data from the Istanbul Rapid Response Network, to underline the importance of fully probabilistic site response analysis in seismic microzonation, aiming to improve the reliability of ground motion predictions and support informed decision-making in earthquake engineering.

Title - Earth, Fire, Wind and Water: Research needs to understand vulnerability to the 4 elements

Abstract: In the field of vulnerability and risk to natural hazards, earthquake engineering has led the way. This includes providing exposure taxonomies, post-earthquake damage data, and the definition of empirical, numerical, and judgement-based approaches for the development of fragility functions. This dominance of earthquake engineering in risk modelling is underpinned by a history of high earthquake losses, and by close collaboration between researchers working on hazard with those working on the hazard performance of engineered infrastructure. This has not necessarily been the case for other hazards, where silos still exist between hazard scientists and engineers. However, with climate and sea level rise projections predicting the higher frequency and intensity of meteorological and hydraulic hazards, it is becoming of growing importance to better understand risk from these. In this talk the four classical Greek elements of Earth, Fire, Wind and Water will be used to frame discussions around the state of art of fragility functions to different hazards. Drawing on past experience and current research, examples will be provided of the strong challenges that exist in deriving fragility models for tsunami, landslides, man-made fires and extreme winds. It will be shown that although advances made in earthquake risk assessment have had significant positive influence, they have at times negatively biased the development of fragility models for other (non-earthquake) hazards. In particular, multi-hazard fragility of buildings to earthquake ground shaking combined with fire and tsunami will be presented to highlight the importance of hazard-specific considerations for structural loading and damage representation in infrastructure. Throughout, the talk will highlight significant data and research gaps that need to be filled to better understand community and infrastructure risk to the four elements of an equal degree.