The quantification of low-probability–high-consequences events: part I. A generic multi-risk approach

Dynamic risk processes, which involve interactions at the hazard and risk levels, have yet to be clearly understood and properly integrated into probabilistic risk assessment. While much attention has been given to this aspect lately, most studies remain limited to a small number of site-specific multi-risk scenarios. We present a generic probabilistic framework based on the sequential Monte Carlo Method to implement coinciding events and triggered chains of events (using a variant of a Markov chain), as well as time-variant vulnerability and exposure. We consider generic perils based on analogies with real ones, natural and man-made. Each simulated time series corresponds to one risk scenario, and the analysis of multiple time series allows for the probabilistic assessment of losses and for the recognition of more or less probable risk paths, including extremes or low-probability–high-consequences chains of events. We find that extreme events can be captured by adding more knowledge on potential interaction processes using in a brick-by-brick approach. We introduce the concept of risk migration matrix to evaluate how multi-risk participates to the emergence of extremes, and we show that risk migration (i.e., clustering of losses) and risk amplification (i.e., loss amplification at higher losses) are the two main causes for their occurrence.     

Predictive ground motion scaling in Switzerland: Best estimates and uncertainties

Spectral ground motion (1 to 15 Hz) as a function of distance is modeled for events spanning 3.0 <M_w ≤ 7.0 in Switzerland. The parameters required to simulate ground motion with a stochastic approach are inverted from 2958 horizontal and vertical component waveforms of small to moderate size events (2.0 ≤ M_{L} ≤ 5.2) in the distance range 10 to 300 km recorded on hard rock sites. Using a Monte Carlo simulation, we establish a significantly different amplification of about a factor of 1.9 between the Alpine Foreland and the Alps. To assess the trade-off between the free parameters of our stochastic model and their influence on the predictive ground motion relationship, we perform a grid search over the five-dimensional solution space. The uncertainties are separated into epistemic and aleatory parts; the main epistemic uncertainty is attributed to the lack of data forM > 5. To constrain the viable models at large magnitudes, results from worldwide scaling studies are evaluated in light of the Swiss data. The model that explains best the low observed stress drops at small magnitudes (Δσ ≅ 3 bar) yet matches observed intensities of historical earthquakes assumes a stress drop increasing with moment asM₀^0.25. For three sites in Switzerland we evaluate the sensitivity of the epistemic uncertainty by computing probabilistic hazard curves. Our model offers the most comprehensive and detailed study of spectral ground motion for Switzerland to date.     

Earthquake scenarios for the city of Basel

Damage scenarios for Basel (Switzerland) are presented, based on a microzonation study and on the distribution of buildings in the different districts of the city. Two reference scenarios are assumed, corresponding to an event with an intensity between VII and VIII and a return period of 475 years, and an event that simulates the 1356 Basel earthquake with an intensity of IX in the city. The overall building damage in the different districts ranges between 8 and 20% for the intensity VII–VIII scenario, while for the intensity IX scenario values range from 31 to 56%. The variation in building vulnerability class within the city and the variability of local ground conditions affect the overall damage significantly, so that their influence on earthquake damage can accumulate or cancel for single districts.     

Applying the relative hypocentre location approach: where was the 1980 November 23 Irpinia earthquake?

The purpose of this work is to evaluate under what conditions it is feasible and with what accuracy it is possible to locate the nucleation point of a large earthquake, given the availability of aftershocks located with high precision by the deployment of a local network. We experiment with several approaches and apply them lo the location of the epicentre of the 1980 November 23 Irpinia earthquake ( M ^w= 6.9).
First we use local P ^g phases selected to optimize the azimuthal coverage, obtaining a well-constrained location with a small statistical error, which typically underestimates the true hypocentre uncertainty.
We then exploit the relative location technique, obtaining stable, almost coincident solutions under three conditions: (1) using multiple independent master events to derive an average epicentre; (2) fitting simultaneously the larger data set for all available master events, using a forward approach; (3) conducting an a priori evaluation of the statistics of station and master events to separate model uncertainties and improve the statistical accuracy of the relative locations. Moreover, only by introducing station statistics can we achieve the desired accuracy of ≅ 1 km in constraining the rupture nucleation point of this large earthquake, and we show that the application of the relative location technique to uncleaned, unweighted data for a single master event provides only a crude epicentre with a confidence ellipse deceivingly smaller than the true hypocentre uncertainty.
The revised epicentre for the 1980 November 23 Irpinia earthquake (48.803 °N-15.302°E) validates the class of multidisciplinary reconstructions of the source process such as the model of Valensise et al. (1989), based on the hypocentre of Westaway & Jackson (1987), and is shifted by almost 13 km to the NW of the epicentre recently proposed by Westaway (1992).     

Seismic hazard map of the Middle East

The collaborative project Earthquake Model of the Middle East (EMME, 2010–2015) brought together scientists and engineers from the leading research institutions in the region and delivered state-of-the-art seismic hazard assessment covering Afghanistan, Armenia, Azerbaijan, Cyprus, Georgia, Iran, Iraq, Jordan, Lebanon, Palestine, Pakistan, Syria and Turkey. Their efforts have been materialized in the first homogenized seismic hazard model comprising earthquake catalogues, mapped active faults, strong motions databank, ground motion models and the estimated ground motion values for various intensity measure types and relevant return periods (e.g. 475–5000 years). The reference seismic hazard map of the Middle East, depicts the mean values of peak ground acceleration with a 10% chance of exceedance in 50 years, corresponding to a mean return period of 475 years. A full resolution poster is provided with this contribution.     

Late Holocene palaeoenvironmental evolution of the Roman harbour of <Emphasis Type="Italic">Portus</Emphasis>, Italy

We present a Holocene record of climate and environmental change in central New York (USA) inferred using lithologic and stable isotope data from two sediment cores recovered in Cayuga Lake. The record was divided into three intervals: (1) early Holocene (~11.6–8.8 ka), (2) Hypsithermal (~8.8–4.4 ka), and (3) Neoglacial (~4.4 ka to present). The early Holocene began abruptly, with rising lake level and relatively deep water. Between ~10.8 and 9.2 ka, cool and dry conditions prevailed at a time of maximum solar insolation. This anomaly has been referred to as the “post-Younger Dryas climate interval” and lasted ~1,600 years, the approximate length of one “Bond cycle.” The Hypsithermal was the warmest, wettest and most biologically productive interval of the Holocene in central New York. The Hypsithermal was characterized by centennial to multi-centennial-scale variability. The 8.2 ka event is one such variation. The Neoglacial was an interval of generally cooler and dryer conditions, falling lake levels, and several prominent climate anomalies. At approximately 2.4 ka, δ¹³C of bulk organic matter increased abruptly by 5‰ as lake level declined, and the lake flora was dominated by Chara sp. during the coldest interval of the Neoglacial. Numerous sediment variables display increased variability ~2.0 ka, which continues today. Archaeological data from the literature suggest that Native American populations may have been large enough to impact land cover by about 2.4 ka and we hypothesize that the “Anthropocene” began at about that time in central New York. We also found paleolimnological evidence for the Medieval Warm Period (~1.4–0.5 ka), which was warmer and wetter than today, and for the Little Ice Age (~500–150 years ago), a period with temperatures colder than today.