Attenuation of intensities in the United States

abstract Isoseismal maps for a number of earthquakes were analyzed to study the attenuation of intensities with distance for different regions of the United States. A graphical method for the estimation of an initial set of epicentral intensities, Io, from the intensity-distance plot for different earthquakes was used, thus avoiding the need to equate the maximum reported or mapped intensity with Io. The attenuation relations were derived by using an iterative least-squares fit procedure, wherein an initial approximate estimate of Io for each earthquake is successively improved. As a by-product, the analysis yielded improved estimates of Io for each earthquake. These Io values were used to derive empirical relations between felt area and epicentral intensities for different regions.