Evaluación del riesgo sísmico mediante métodos avanzados y técnicas GIS. Aplicación a la ciudad de Barcelona.

Este trabajo es una contribución al desarrollo y aplicación de métodos avanzados de análisis de riesgo sísmico en grandes ciudades y se ha estructurado en dos partes: la primera establece el marco teórico de los estudios de riesgo sísmico, detallando los modelos y desarrollos avanzados para la evaluación del daño físico sobre edificios residenciales y de su impacto sobre la población, así como otros aspectos con él relacionados; la segunda describe la aplicación a Barcelona. Se usan dos métodos que se aplican a dos escenarios. El primer método, al que nos referimos como Método del Índice de vulnerabilidad (MIV), considera cinco estados de daño no nulo, define la acción en términos de intensidad macrosísmica y el edificio mediante un índice de vulnerabilidad; el grado de daño esperado se efectúa mediante funciones semiempíricas que dependen de la intensidad y del índice de vulnerabilidad. El segundo método, al que nos referimos como Método del Espectro de Capacidad (MEC) considera cuatro estados de daño no nulo, define la acción sísmica en términos de espectros de respuesta, y el edificio por medio de su espectro de capacidad. El grado de daño esperado se obtiene mediante el desarrollo de curvas de fragilidad y matrices de probabilidad de daño. Para la aplicación de ambos métodos a Barcelona se usa un escenario determinista y uno probabilista. Otra de las aportaciones relevantes de esta investigación es la creación de una herramienta, potente y versátil, diseñada sobre un Sistema de Información Geográfica (SIG) o Geographic Information System (GIS). Esta aplicación permite la integración, explotación y gestión de los datos. Este tipo de programas es imprescindible para cartografiar escenarios georreferenciados y va más allá de la aplicación concreta, pues su actualización es rápida y es de fácil adaptación para estudios de otros riesgos en la misma ciudad o en otras ciudades.Los resultados obtenidos son consistentes con la evolución histórica de la ciudad y con su condición actual, así como con las características de los suelos, poniendo de manifiesto la robustez de los métodos empleados. En general se observa una estructura radial del daño esperado con un mayor daño en Ciutat Vella y menor daño en los distritos periféricos. Destaca también el daño esperado en los pequeños núcleos de los pueblos antiguos de los actuales distritos. El MIV representa mejor las peculiaridades de los edificios individuales. El MEC suaviza estas características clasificando los edificios en 6 clases. El escenario más favorable es el determinista cuando se analiza mediante el MEC con daños esperados entre nulo, leve y moderado; el grado de daño medio de la ciudad es leve. Los más desfavorables son el determinista y probabilista cuando se analizan con el MIV; en ambos casos el estado de daño medio global es moderado. El distrito de l'Eixample destaca por ser el de mayor riesgo debido a la vulnerabilidad de sus edificios, a la alta densidad de edificios y población y al valor expuesto. Se confirma que, en ciudades como Barcelona, situadas en regiones de peligro sísmico entre bajo y moderado, la escasa o nula conciencia del peligro sísmico y la ausencia de precauciones de protección sísmica conduce a una elevada vulnerabilidad de sus edificios y, consecuentemente, a un elevado riesgo. En efecto, para escenarios relativamente moderados, con intensidades entre VI y VII, se esperan daños considerables. Los daños a la población son relevantes y su evaluación es muy sensible a los modelos de víctimas. En este sentido es preciso considerar los valores numéricos concretos como pronósticos del orden de magnitud de las cantidades evaluadas, y, en cualquier caso, se deben interpretar, desde una óptica probabilista, como valores medios para escenarios sísmicos creíbles.Los resultados de este estudio son de una enorme utilidad para la prevención y minoración del riesgo sísmico y para la planificación y gestión de emergencias

Vulnerability index and capacity spectrum based methods for urban seismic risk evaluation. A comparison

This article contributes to the development and application of two latestgeneration methods of seismic risk analysis in urban areas. The first method, namely vulnerability index method (VIM), considers five non-null damage states, defines the action in terms of macroseismic intensity and the seismic quality of the building by means of a vulnerability index. The estimated damage degree is measured by semi-empirical functions. The second method, namely capacity spectrum based method (CSBM), considers four no damage states, defines the seismic action in terms of response spectra and the building vulnerability by means of its capacity spectrum. In order to apply both methods to Barcelona (Spain) and compare the results, a deterministic and a probabilistic hazard scenario with soil effects are used. The deterministic one corresponds to a historic earthquake, while the probabilistic seismic ground motion has a probability of exceedence of 10% in 50 years. Detailed information on the building design has been obtained along years by collecting, arranging, improving, and completing the database of the dwellings of the city. A Geographic Information System (GIS) has been customized allowing storing, analysing, and displaying this large amount of spatial and tabular data of dwellings. The obtained results are highly consistent with the historical and modern evolution of the populated area and show the validity and strength of both methods. Although Barcelona has a low to moderate seismic hazard, its expected seismic risk is significant because of the high vulnerability of its buildings. Cities such as Barcelona, located in a low to moderate seismic hazard region, are usually not aware of the seismic risk. The detailed risk maps obtained offer a great opportunity to guide the decision making in the field of seismic risk prevention and mitigation in Barcelona, and for emergency planning in the city

Evaluation of social context integrated into the study of seismic risk for urban areas

Usually the seismic risk evaluation involves only the estimation of the expected physical damage, casualties or economic losses. This article corresponds to a holistic approach for seismic risk assessment which involves the evaluation of the social fragility and the lack of resilience. The complementary evaluation of social context aspects such as the distribution of the population, the absence of economic and social development, deficiencies in institutional management, and lack of capacity for response and recovery; is useful in order to have seismic risk evaluation suitable to support a decision making processes for risk reduction. The proposed methodology allows a standardized assessment of the social fragility and lack of resilience, by means of an aggravating coefficient of which summarizes the characteristics of the social context using fuzzy sets and Analytic Hierarchy Process (AHP). The selection of 20 social indicators is based on the indicators used by urban observatories of United Nations and other social researchers. These indicators are classified according to social item they describe, in six categories. Applying the determination level analysis, thirteen prevailing social indicators are selected. The proposed methodology has been applied in the cities of Merida (Venezuela) and Barcelona (Spain

Evaluation of social context integrated into the study of seismic risk for urban areas

Usually the seismic risk evaluation involves only the estimation of the expected physical damage, casualties or economic losses. This article corresponds to a holistic approach for seismic risk assessment which involves the evaluation of the social fragility and the lack of resilience. The complementary evaluation of social context aspects such as the distribution of the population, the absence of economic and social development, deficiencies in institutional management, and lack of capacity for response and recovery; is useful in order to have seismic risk evaluation suitable to support a decision making processes for risk reduction. The proposed methodology allows a standardized assessment of the social fragility and lack of resilience, by means of an aggravating coefficient of which summarizes the characteristics of the social context using fuzzy sets and Analytic Hierarchy Process (AHP). The selection of 20 social indicators is based on the indicators used by urban observatories of United Nations and other social researchers. These indicators are classified according to social item they describe, in six categories. Applying the determination level analysis, thirteen prevailing social indicators are selected. The proposed methodology has been applied in the cities of Merida (Venezuela) and Barcelona (Spain).Peer ReviewedPostprint (published version

Effect of rockfall fragmentation on exposure and subsequent risk analysis

Rockfalls are frequent natural processes in mountain regions with the potential to produce damage. The quantitative risk analysis (QRA) is an approach increasingly used to assess risk and evaluate the performance of mitigation measures. In case of the fragmentation of the falling rock mass, some of the hypothesis taken in the QRA estimation for rockfalls have to be modified since a single block or rock mass can produce several fragments thus modifying the runout probability, the impact energies and exposure of the elements at risk. In this contribution, we present a procedure to account for the exposure in QRA analysis along linear paths using the fragmental rockfall propagation model RockGIS (Matas et al. 2017). The procedure is applied at the “Monasterio de Piedra”, Spain as part of a QRA.Postprint (published version

Disaster risk reduction: a decision-making support tool based on the morphological analysis

Risk management due to natural hazards is a multidimensional and complex problem since it requires the knowledge and experience of several disciplines. The effectiveness of risk management can be analyzed, inviting to the action through weakness identification of the urban area. This article proposes a methodology based on the morphological analysis to support the decision-making on disaster risk management, taking as a starting point the results of a holistic evaluation of the seismic risk. The results of the holistic evaluation of risk are achieved aggravating the physical risk using the contextual conditions, such as the socio-economic fragility and the lack of resilience. In consequence, the risk mitigation can be performed through the reduction of the potential damage and consequences involved; and the improvement of social conditions. The proposed methodology allows prioritizing the risk reduction strategies according to i) performance level of component indicators involved into the Disaster Risk Management index, DRMi; ii) physical risk factors dependent from the potential damages, and iii) aggravating factors involved in the aggravating coefficient. Moreover, it involves 35 strategies to reduce the physical risk and the aggravating social conditions of the urban area. The proposed methodology has been applied to the city of Mérida (Venezuela), located within an area of high seismic activity. The performance level of the indicators involved in the DRMi was evaluated by a survey to local experts. As a result, eleven strategies have been identified to reduce the potential damage and to improve the social conditions of this city.Peer ReviewedPostprint (author's final draft

Automatic manhole extraction from MMS data to update basemaps

Basemaps are the main resource used in urban planning, building and infrastructure asset management. Therefore, they must be accurate and up to date to better serve citizens, contractors, property owners and town planning departments. Traditionally, they have been updated by aerial photogrammetry, but this is not always possible and alternatives need to be sought. In such cases, a useful option for large scales is the mobile mapping system (MMS). However, automatic extraction from MMS point clouds is limited by the complexity of the urban environment. Therefore, the influence of the urban pattern is analysed in three zones with varied urban characteristics: areas with high buildings, open areas, and areas with a low level of urbanization. In these areas, the capture and automatic extraction of 3D urban elements is performed using commercial software, which is useful for some elements but not for manholes. The objective of this study is to establish a methodology for extracting manholes automatically and completing hidden buildings' corners, in order to update urban basemaps. Shape and intensity are the main detection parameters for manholes, whereas additional information from satellite image Quickbird is used to complete the buildings. The worst rate of detection for all the extracted urban elements was found in areas of high buildings. Finally, the article analyses the computing cost for manhole extraction, and the economic cost and time consume of the entire process, including the proposed methodolgy using an MMS point cloud and the traditional survey in this case.Peer ReviewedPostprint (updated version

Sostenible - No sostenible

Esta breve contribución, dentro del bloque temático “Iniciativas-motor de cambio”, contiene una idea principal: la insostenibilidad intrínseca del desarrollo humano. Afortunadamente, esta “no-sostenibilidad” es sólo un tema de nomenclatura que se refiere al significado literal del término; no es un problema de fondo que cuestione la necesidad de desarrollar políticas y estrategias orientadas al Desarrollo Humano “Sostenible” (DHS).Peer Reviewe