Although earthquakes in the central and eastern U.S. are much less frequent than in the western U.S., they are typically felt over a much broader region. East of the Rocky Mountains, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast. Western rock is relatively young, which means it absorbs a lot of the shaking caused by earthquakes. Thus, western earthquakes result in intense shaking close to the epicenter, but fade more quickly the farther the earthquakes travel. In the eastern United States the rock is far older, and the earthquake energy can therefore spread farther and have a greater impact. A magnitude 5.5 eastern U.S. earthquake can usually be felt as far as mi (km) from where it occurred, and sometimes causes dam