Isoseismal map for the January 25, 2001, mainshock at Ashtabula. The map depicts areas of approximately equal Modified Mercalli intensities as reported by residents in the areas in which the earthquake was felt or caused damage. Maximum Modified Mercalli intensity was VI at some locations in Ashtabula. Note the elongation of the felt area northward into Ontario and the abrupt southward termination in northeastern Ohio and northwestern Pennsylvania. A similar phenomenon was evident on the felt-area map for the 1998 Pymatuning earthquake in northwestern Pennsylvania. Ohio Seismic Network stations have noted a north-south asymmetry of waveforms for lakeshore earthquakes. The cause of this phenomenon is unknown. Map prepared by Margaret Hopper of the U.S. Geological Survey. Canadian intensities courtesy of Sylvia Hayek of the Geological Survey of Canada.