SYSTEMIC UNCERTAINTIES AND DECISION SUPPORT APPLICATIONS IN REGIONAL SEISMIC LOSS ANALYSES
A number of tools and advancements have been developed over the course of the last decade for public use in regional seismic disaster planning. This paper addresses some of the considerations and approaches that influence state-of-theart regional seismic loss assessments and risk management, with particular emphasis on approaches applied to areas having potentially high consequence but low probability seismic hazards in the United States. The various components of regional seismic loss assessment are synthesized within a GIS-based framework, including the aggregation and propagation of uncertainties inherent in the analysis. The threat posed by ground shaking and ground failure hazard effects is estimated and mapped onto high resolution point-wise building stock and bridge inventory assets. Inventory vulnerability is assigned based on structural classifications of construction materials, together with general system configurations and lateral resisting system types. Likelihood of damage to the built environment is then determined by the combination of the hazard and vulnerability for each building and bridge, and social and economic consequences are projected based on correlation with descriptions of physical damage levels, both in terms of expected values, and dispersions of the aggregate regional analysis output. Decision support algorithms are also discussed, which leverage the high resolution of the regional analysis output to focus mitigation planning and capital investment on particularly sensitive and influential assets within study regions.
A DAMAGE SCENARIO FOR THE CITY OF MESSINA , ITALY , USING DISPLACEMENT-BASED LOSS ASSESSMENT
An earthquake damage scenario for the city of Messina, Italy, has been carried out with the aim of forecasting the distribution of different levels of structural damage within the city. These results can be of use to the Civil Protection Department and other services for disaster planning management. Field surveys were carried out in order to calibrate the model to the building stock characteristics of Messina. On the basis of these surveys, different structural typologies, which group buildings with similar features, were characterized. The probability of exceeding a given damage state for each group of buildings (which included both reinforced concrete and masonry construction), was computed through a recently developed probabilistic displacement-based vulnerability procedure. This study has highlighted the high seismic risk of the city of Messina, caused by both its high level of hazard as well as the significant vulnerability of its building stock. Work currently underway now aims at the identification of the effects that debris stemming from the collapse of the buildings could have on the road network, with a view to assess if, after a seismic event, rescue and emergency teams would be in a position to access the most damaged areas of the city and then reach the hospitals and other emergency support facilities.
Igneous Rock Associations 23. The Bushveld Complex, South Africa: New Insights and Paradigms
SUMMARYThe Bushveld Complex has continued to serve as the basis for study into the fundamental nature of petrological processes for layered intrusion formation and for oxide and sulphide hosted Platinum Group Element (PGE)–Cu–Ni ore deposits. These studies have included discoveries in terms of the physical extent of Bushveld magmatism, both laterally and internally. Lateral variations in the mafic to ultramafic Rustenburg Layered Suite of the Northern Lobe of the complex have also revealed petrologically distinctive Upper Critical Zone equivalent rocks (the so-called Flatreef) with enhanced contamination and mineralization traits that reflect a transition between Eastern and Western Lobe equivalent stratigraphy and Platreef-style complexity. Traditional magma mixing models have been re-examined in light of radiogenic isotopic evidence for crustal involvement early in the chromite precipitation or formation process, combined with evidence for associated heterogeneous fluid contents, cryptic layering profiles, and textural evidence. A wide variety of alternative ore-genesis models have been proposed as a consequence. The fundamental mechanics of magma chamber processes and the existence of the magma chamber as an entity have been called into question through various lines of evidence which have promoted the concept of progressive emplacement of the complex as a stack of not-necessarily-quite-sequentially intruded sills (with or without significant quantities of transported phenocrysts), emplaced into variably crystallized and compacted crystal-liquid mush mixtures, modified by compaction-driven late magmatic fluid (silicate and aqueous) activity. Alternatively, petrological and geochemical observations have been used to discount these interpretations in favour of more conventional cooling and gravity-driven accumulation of silicate and ore minerals in a large, liquid-dominated system.RÉSUMÉLe complexe de Bushveld a demeuré à la base d’études sur la nature fondamentale des processus pétrologiques de formation d’intrusions litées et des gîtes des éléments du groupe platine (ÉGP)-Cu-Ni hébergés dans les oxydes et les sulfures. Ces études ont comporté des découvertes sur l’étendue physique, à la fois latérale et interne, du magmatisme de Bushveld. Les variations latérales de la suite stratifiée et mafique à ultramafique Rustenburg du lobe nord du complexe ont également révélé des roches équivalentes pétrologiquement distinctes de la zone critique supérieure (le communément désigné Flatreef) avec des traits de contamination et de minéralisation accrus qui reflètent une transition entre la stratigraphie équivalente des lobes est et ouest et la complexité de type Platreef. Les modèles traditionnels de mélanges magmatiques ont été réexaminés à la lumière de preuves isotopiques radiogéniques indiquant une implication de la croûte au début du processus de précipitation ou de formation de la chromite, combinées à des preuves de contenu fluide hétérogène associé, de profils de litage cryptique et de preuves texturales. Ainsi, une grande variété de modèles alternatifs de genèse de minerai a été proposée. La mécanique fondamentale des processus de la chambre magmatique et l'existence de la chambre magmatique en tant qu'entité ont été remises en question au moyen de divers éléments de preuve qui ont mis en avant le concept de mise en place progressive du complexe sous forme d'un empilement non-nécessairement séquentiel de sills injectés (avec ou sans quantités significatives de phénocristaux transportés) mis en place dans des mélanges de bouillie cristaux/liquide à cristallisation et compaction variable, modifiés par une activité tardive de fluide magmatique (silicaté et aqueux) induite par la compaction. Alternativement, des observations pétrologiques et géochimiques ont été utilisées pour écarter ces interprétations en faveur d'un processus plus conventionnel de refroidissement et d’accumulation de minérais silicatés et minéralisés induite par la gravité dans un vaste système à dominance liquide.