Displacement spectral densities and spatial attenuation of Lg waves from four earthquakes were studied in detail to determine the applicability of Nuttli's (1973) Lg-magnitude formulas to northeastern North American earthquakes. It was found that the 1-sec-period Lg wave from these events was attenuated at a slightly greater rate than has been observed in the central United States. However, comparison of the A/T observations and the Lg spectral analysis results of the two regions demonstrated that it was permissible to use Nuttli's Lg-magnitude formulas for scaling northeastern earthquakes if the amplitude observations are restricted to within 20° of the earthquake's epicenter. This result establishes the basis for a unified mb magnitude scale between central and northeastern North America.

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