Evaluación del potencial sísmico de la península de Nicoya

La brecha sísmica de Nicoya es un segmento de la zona de subducción ubicado costa afuera y por debajo de la Península de Nicoya en el noroeste de Costa Rica, región Chorotega. Este segmento de la Trinchera Mesoamericana, donde la placa del Coco se subduce por debajo de la placa del Caribe, ha sufrido tres rupturas, documentadas en tiempos históricos, produciendo grandes sismos en 1853, 1900 y 1950. El fuerte acople de este segmento contrasta con el acople débil de los segmentos adyacentes: el segmento de Nicaragua hacia el NO y el de Costa Rica central hacia el SE. El segmento de Nicaragua tiene un nivel muy alto de sismicidad de fondo, con ocurrencia anual de muchos sismos que sobrepasan la magnitud de 5.0 grados; su más reciente gran evento fue un sismo anormalmente lento con magnitud de momento (Mw) de 7.6 grados y que generó un tsunami destructivo en 1992. El segmento central de Costa Rica, también tiene un alto nivel de sismicidad de fondo con eventos muy frecuentes que alcanzan magnitudes superiores a 4.5 grados; su más reciente evento de importancia (Mw=7.0) ocurrió en marzo de 1990 en la zona de contacto entre este segmento y la brecha sísmica de Nicoya. Las réplicas de los sismos de Costa Rica en 1990 y de Nicaragua en 1992, ocurridos en los segmentos adyacentes, permitieron demarcar la posición geográfica de la brecha sísmica de Nicoya. Las evidencias que indican la existencia de un fuerte acople sísmico en el segmento de Nicoya son: a) un bajo nivel de sismicidad de fondo; b) el cese repentino de la propagación de las réplicas de los sismos mencionados de 1990 y de 1992 justo en los bordes de la brecha sísmica de Nicoya; y c) el rápido movimiento (de cerca de 30 mm/año) hacia el NE (en dirección paralela a la convergencia entre las placas del Coco y del Caribe) de la Península de Nicoya observado con sistemas de posicionamiento global por satélite (GPS), según fueron reportados por Lundgren et al., 1999. El fuerte acoplamiento elástico entre las placas del Coco y del Caribe puede ser causado por la carga litostática (peso de la columna de rocas) que ejerce la Península de Nicoya sobre la interface de las dos placas. El muy limitado deslizamiento sísmico que se ha producido en el segmento de Nicoya desde 1950, la rápida tasa de convergencia entre las placas del Coco y del Caribe de alrededor de 88 mm/año y considerando que el área de este segmento de la zona de subducción oscila entre 4600 y 9600 km², sugieren que la brecha sísmica de Nicoya ha alcanzado ya el potencial para producir un sismo con una magnitud de momento cercana a los 7.5. La presencia de la Península de Nicoya sobre el área de ruptura (lo cual facilita la instrumentación y observación) y su alto potencial sísmico fueron las dos características más importantes que hicieron que este segmento fuera seleccionado, por un panel de científicos a nivel mundial, como uno de los dos sitios sismogénicos en los que se está realizando el "experimento de zonas sismogénicas", SEIZE: Seismogenic Zone Experiment (el otro sitio seleccionado es Nankai, en Japón). Este experimento es una iniciativa conjunta de universidades de tres continentes (América, Europa y Asia) y cuya contrapartida en Costa Rica es el Observatorio Vulcanológico y Sismológico de Costa Rica, de la Universidad Nacional (OVSICORI-UNA), entidad estatal con sede en Heredia.(AU)

Survey research in disaster public health

Introduction: While much has been learned during the past three decades of research in the disaster field, there still are some major gaps in knowledge. The need for more and better research on the health aspects of disasters is specially noted. Often, research into the health aspects has been anecdotal in nature and suffers from poor documentation of human losses. However, there are valid research metodologies that can be adapted to better document losses, evaluate interventions and set priorities for investments to reduce the burden on the health of the population caused by disasters. Methods: A number of data sources are used to demonstrate the potential uses of surveys in disaster health. The majority of the examples reflect data collected by telephone interviews following eartquakes in California. Results: By using comparable instruments, it is possible to track the changes in preparedness levels across the time. Similarly, it is possible to compare injury rates or other health impacts across time, place and disaster type. In addition, risk factors can be identified for health outcomes. For example, in the Northridge eartquake, those over age 60 years were three times more likely to be hospitalized or die as a result of injuries than were those aged 20-59 years. Interventions can be evaluated. Slightly less than half of the respondents of the El Niño study had heard messages about preparing for the on-coming weather and their preparedness levels were not significantly different from those who had not heard about preparing for the weather. Conclusion: Surveys are useful tools for identifying and evaluating the health impacts of disasters (AU)

Paradigmatic disaster? : The crash of trans world airlines (TWA) flight 800

This paper uses two discourses - Kuhnïs (1962) formulation of paradigm and cognitive theory (specifically that of social schemas) -to deconstruct the Federal Bureau of Investigation (FBI) and National Transportation Safety Boardïs (NTBïS) investigation into the 1996 TWA Flight 800 disaster. Following the disaster, concerns were expressed in the media that the FBI and NTSB might not be approaching the investigation with an entirely open mind. Certainly a number of statements were made by FBI and NTSB managers that seemed to indicate a preferred conclusion as to cause(s) of the disaster. This paper uses social schema theory and Kuhnïs discourse on the paradigm to ascertain, on the basis of widely reported statements, the degree to which the FBI and NTSB investigators stated a preference- expressed either overtly in statements, or covertly through investigative method- in the matter of causation (AU)

Property modification factors for seismic isolation bearings

The overall objective of this task was to develop an improved understanding of the expected performance and behavior of sliding isolationsystems;evaluate their functionality, reliability, and longevity; and assist in the development of improved codes and specifications for their use. This report deals with the problem of establishing upper and lower bound values of properties of seismic isolation bearing for use in the analysis and design of seismicallyisolated bridges. These bounding values of properties are determined by using system property modification factors. The concepts and the values presented represent the basis on which bounding analysis is described in the new 1999 "AASHTO Guide Specifications for Seismic Isolation Design"

INCEDE : At the end of a decade : Summarizing its 8-year activities

United States (UN) declared 1990-2000 as the International Decade for Natural Disaster Reduction (IDNDR). The International Center for Disaster-mitigation Engineering (INCEDE) was established in April 1991, within a year after the UN declaration, as a national contribution of Japan towards UN initiative of natural disaster reduction. The center was established in a university environment at Institute of Industrial Science (IIS) of the University of Tokyo with the objectives of doing fundamental research on various aspects of disaster reduction and tackling problems in disaster mitigation through synthesizing information and methodologies from different fields, mainly from earthquake, water induced disasters, remote sensing and GIS fields.(AU)

Towards a critical sociology of risk

Sociologists are growing increasingly skeptical toward research on risk conducted in other fields, and new perspectives on risk are emerging. Topics that merit further exploration include the social construction of risk and risk objects, risk analysis as a type of scientific enterprise, the organizational and institutional forces that shape positions on risk, safety and risk as dynamic properties of social systems, and the social forces that create and allocate risk. In particular, sociologists need to place more emphasis on exploring the roles played by organizations and the state in hazard production and on formulating a political economy of risk. To a significantly greater degree than other disciplines concerned with risk, sociology emphasizes the contextual factors that structure vulnerability to hazards and the linkages that exist between vulnerability and social power

Response modification factors for seismically isolated bridges

The 1997 AASHTO "Guide Specifications for Seismic Isolation Design" specify response modification factors for the substructures of isolated bridges that are lower than those specfied for the substructures of non-isolated bridges. this report presents the rationale behind these specifications and presents reseach results that lead to the establishment of appropriate response modification factors for isolated bridges. The reseach concertrated on dynamic analysis of simple models of seismic-isolated and non-isolated bridges for a range of isolation system and substructure behaviors and for seismic excitation characterized by AASHTO ground motion spectra for a range of soil conditions and acceleration coefficients. the study investigated the displacement ductility demand in the substructure of these bridges and established the appropriate value of the ductility-based portion of the response modification factors.The study concludes that response modification factors should be lower in the substructures of isolated bridges than in the substructures of non-isolated bridges because : A) elastic or nearly elastic substructure behavior is required for proper behavior of the isolation system, and B) isolated bridges exhibit more sensivity in the substructure ineslastic response due to variability the seismic input (AU)

Características meteorológicas y oceanográficas en el Pacífico Sudeste durante la declinación del evento El Niño 1997-1998. Crucero Regional Conjunto. Mayo de 1998

Se analizaron las condiciones oceanográficas y meteorológicas registradas durante mayo y primeros días de junio de 1998, en los cruceros de investigación oceanográfica que fueran ejecutados por Colombia, Ecuador, Perú y Chile, y coordinados por la Comisión Permanente del Pacífico Sur (CPPS), como contribución a la celebración del Año Internacional de los Océanos. Durante el crucero se descubrión un área comprendida entre 7 grados Norte y 25 grados Sur mediante la ejecución de 286 estaciones oceanográficas, en las cuales se tomaron datos meteorológicos, oceanográficos, biológicos, desde la superficie hasta un aprofundidas máxima de 500 metros. Las condiciones oceanográficas de mayo/98, se caracterizraon por una disminución notable de las anomalías térmicas desde la zona ecuatorial central hacia el sur. En total se registraron 6 masas de agua: Agua Tropical Superficial (ATS), Agua Ecuatorial Superficial (AES), Agua Subtropical Superficial (ASTS), Agua Subantártica (ASAA), Agua Intermedia Antártica (AIA), y Agua de la Cuienca Colombiana (ACC), siendo el Agua Subtropical Superficial la que predominó en el área investigada, modificando los procesos de surgencia costera. Las condiciones oceanográficas y meteorológicas que caracterizaron al evento ENOS (El Niño/Oscilación del Sur) 1997-98 y que alcanzaron su máxima expresión durante el verano austral, presentaba indicios de un progresivo retorno hacia condiciones normales, especialmente al sur de los 10 grados de latitud sur.(AU)