Spectral Characteristics of the Lg wave Generated by Central United States Earthquakes

Abstract

Spectra of more than three hundred short-period, vertical component Lg waves of 78 earthquakes in the central United States were determined. From these an empirical relationship between the long-period level of the Lg spectrum and the seismic moment was developed. The shape of the reduced spectrum shares some characteristics of Aki's revised model A. There is a uniform relationship between the corner period and the seismic moment, which implies a uniformity of earthquake processes in the central United States over a wide range of event sizes, as opposed to California where wide variations in the corner frequency are observed for source spectra having the same seismic moment. Using the reduced spectra, a method for relating magnitude observations at periods other than 1 s to mb is outlined.