Inge Lehmann was a famous Danish seismologist and the only woman to win the Medal of the Seismological Society of America. She died in 1993 at the age of 105. Her most famous achievement was the discovery of the inner and outer cores of the Earth through the reflection of seismic waves off of those surfaces.
The Modified Mercalli Intensity scale describes how much shaking was experienced at a site, based on interviews and examination of damaged structures. It is not an instrumental determination. Intensity levels range from not felt (I) to total destruction (XII). In contrast, magnitude represents the energy released in the earthquake and is not what you feel in the event. The same earthquake will feel very different at different locations. For each earthquake, we will have one magnitude but a map of intensities with different intensities at different sites. Bigger earthquakes will have larger areas of damage and higher maximum intensities. How large an area of a particular level of shaking (say, VII - where old buildings begin to be damaged) is produced by any earthquake will depend both on the magnitude of the event and on how quickly the waves attenuate with distance. California has a higher attenuation than the East Coast. Earthquake waves lose energy more quickly in California so an earthquake of a particular magnitude will be felt over a much larger area on the East Coast than in California.