Determinación de una relación lineal entre intensidad, magnitud y distancia epicentral para el occidente de Venezuela / Determination of a linear relation between intensity, magnutude and epicentral distance for western Venezuela

Se aplicó el método de Bakun y Wentworth (1997) a siete sismos ocurridos entre 1950 y 1995 en la región occidental y central de Venezuela, para determinar la ecuación que relaciona intensidades con magnitud y distancias epicentrales. Los valores de intensidad fueron obtenidos de diversos catálogos, algunos disponibles a través de Internet. Si las intensidades se restringen a distancias £120km., se obtiene una relación lineal entre intensidad y distancia para una determinada magnitud, dada por I= -2,2237 + 1,6684*MWI -0,041214*(medD), donde I: intensidad, MWI: magnitud de intensidad, y medD: mediana de las distancias epicentrales para un valor particular de intensidad. Esta ecuación fue validada utilizando siete eventos de prueba ocurridos entre 1932 y 1982, lo que demuestra la confiabilidad y utilidad del método para su uso en el análisis de sismos históricos, especialmente de los pre-instrumentales. Este tipo de estudio cobra mayor importancia con la disponibilidad de los datos digitales que aportará la nueva Red Sismológica Nacional de Venezuela, que permitirá ahondar más en el estudio de las relaciones entre parámetros de fuente e intensidades. Las relaciones de atenuación para la cordillera de Mérida y el centro del país difieren significativamente tanto con respecto a California como con respecto al este de los Estados Unidos

Health, biodiversity, and natural resource use on the Amazon frontier: an ecosystem approach

Visa melhorar a saúde das comunidades rurais amazônicas mediante o desenvolvimento e a aplicaçäo de abordagem ecossistêmica participante na avaliaçäo da saúde humana. Na área estudada, oscilaçöes sazonais definem a disponibilidade de alimentos, a qualidade da água e a incidência de doenças. A determinaçäo dos elos causais entre variáveis ecossistêmicas, uso de recursos e saúde exigiu uma gama de formas de investigaçäo, em múltiplas escalas, com participaçäo local. O mapeamento espacial da paisagem quanto ao uso de recursos mostrou a diversidade dos recursos ecológicos de que as comunidades dependem. Inquéritos domiciliares detalharam padröes de consumo e produçäo familiares e individuais. Medidas antropométricas, carga parasitária, qualidade da água e níveis de anemia foram empregados como indicadores do estado de saúde individual e coletivo. Tais marcadores foram complementados com avaliaçäo etnográfica e participante sobre saúde, o que criou a base para desenvolver planos de açäo comunitária para lidar com questöes de saúde. A discussäo enfoca três atributos de abordagem ecossistêmica: (a) pluralismo metodológico, (b) interaçöes transversais, em termos de escala e (c) pesquisa-açäo participante.

Estudio de unas tormentas sismicas en la region de el Aguila y de Piñango, Andes Venezuelanos, entre octubre de 1989 y abril de 1990 / A study of seismic swarms occurred from october 1989 to 1990, in the neighborhood of Pico el aguila and Piñango, Venezuelan Andes

Between October 1989 and June 1990 there were a large number of microearthquakes in the neighborhood of Pico El Aguila and Pinango, Merida State, Venezuela. The epicenters form two clearly separated groups. The first one comprises events which occurred between October 1989 and March 1990. Their epicenters were located between 8.75 degrees N and 8.88 degrees N and between 70.75 degrees W and 70.88 degrees W. They are lined up in a northwest-southeast trend. The zone is crossed in its center by the Bocono fault zone, and the Valera fault is the northwest limit of the epicentral distribution. The second group of microearthquakes was recorded during April 1990, and its epicenters were located between 8.85 degrees N and 9.00 degrees N, and between 70.75 degrees W and 70.90 degrees W. They are lined up in a trend parallel to the first group. The Valera fault forms its southwest border, and the Pinango fault its northwest one. Based on the polarities, six composite focal mechanisms were constructed, three for the first group of events and three for the second one. In the first group, two mechanisms, one in each side of the Bocono fault zone, correspond to reverse faulting. A third mechanism, obtained from events close to the Bocono fault zone, correspond to a right-lateral strike-slip displacement. In the second group, two hanisms correspond to reverse faulting and the third, located in the southwestern end of the lineation, close to the Valera fault, shows a left-lateral strike-slip mechanism. The Angelier graphical method was applied to the six mechanisms, which produced a range of acceptability for the orientation of the maximum stress axes between N 24 degrees W and N 51 degrees W. These characteristics can be explained by a mechanical model, postulated in this work for the study area, which explain the coexistence of reverse, right lateral strike slip and left lateral strike slip faulting under the same stress regime, assuming that this faulting occurs on preexisting faults. Some 25 Km northeast of the study area, the azimuth of the Bocono fault zone is approximately N 49 degrees E. In case that the orientation of the compression axis remains constant, this would mean, from the mechanics point of view, that the Bocono fault zone is a weak one, just as other strike-slip faults such as San Andreas Fault and the Big Sumatra Fault