There are systematic differences in the attenuation of damaging earthquake ground motions between different stable continental regions (SCRs). Seismic intensity and weak-motion data show that the attenuation in seismic waves for eastern North America (ENA) is less than for India, Africa, Australia, and northwest Europe. If ENA ground-motion attenuation relations are used in seismic hazard models for other SCRs, as is commonly done, then the estimated ground motions and resulting hazard may be too large. If an attenuation model that averages observations from ENA and the other SCRs is used to estimate the magnitudes of large historical earthquakes in ENA, as is the case for recent estimates of M for the 1811--1812 New Madrid, Missouri and the 1886 Charleston, South Carolina events, then the magnitude estimates for these events will be too large, as will be the resulting hazard.