Determination of a linear relation between intensity, magnutude and epicentral distance for western Venezuela

The method of Bakun and Wentworth (1997) was applied to seven earthquakes occurred between 1950 and 1995 in Western and Central Venezuela, to determine the equation that relates intensities with magnitude and epicentral distances. The intensity values were obtained from several catalogs, some of them available from Internet. Restricting the intensities to distances up to <= 120km, a linear relationship is obtained between intensity and epicentral distance for a given magnitude, so that I = -2.2237 + 1.6684*M-WI - 0.041214*(med Delta), where I: intensity, M-WI: intensity magnitude, and med Delta: median of epicentral distances, for a given intensity value. This equation was validated using seven test events occurred between 1932 and 1982, demonstrating the reliability and usefulness of the method for the analysis of historical earthquakes, especially of the pre-instrumental ones. This kind of study becomes more significant with the availability of digital data from the new National Seismological Network of Venezuela, which will allow to gain a better understanding of the relationships between source parameters and intensities. The attenuation relationships for the Merida mountain ranges and Central Venezuela differ significantly from both California and the Eastern United States.